ARC

.cargo/config.toml

@@ -1,7 +0,0 @@
-# rustc's LoongArch targets use the medium code model, but the cc crate
-# compiles C code with the C compiler's default normal code model, whose
-# direct calls reach only ±128 MiB, unless -Ccode-model is given
-# explicitly. A debug build of mold has more text than that, so we pass
-# the model explicitly to make the cc crate pass -mcmodel=medium.
-[target.'cfg(target_arch = "loongarch64")']
-rustflags = ["-Ccode-model=medium"]

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,10 @@
+---
+name: Bug report
+about: Create a report to help us improve
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+Delete this message and describe the bug here. Note that we only fix bugs in the most recent release of mold, so please make sure that you are using the most recent version.

.github/workflows/build-all.yml

@@ -3,27 +3,12 @@ name: Build all tarballs
 on:
   schedule:
     - cron: '0 0 * * *'
+  release:
+    types: [ published ]
   workflow_dispatch:
 
 jobs:
-  check-changes:
-    runs-on: ubuntu-24.04
-    outputs:
-      has_changes: ${{ github.event_name == 'workflow_dispatch' || steps.check.outputs.has_changes }}
-    steps:
-    - name: Check for new commits since last successful run
-      id: check
-      env:
-        GH_TOKEN: ${{ github.token }}
-      run: |
-        last=$(gh run list -R ${{ github.repository }} -w build-all.yml -b main -s success -L1 --json createdAt -q '.[0].createdAt')
-        if [ -z "$last" ] || [ "$last" = "null" ] || [ "$(gh api repos/${{ github.repository }}/commits?sha=main\&since=$last\&per_page=1 | jq length)" -gt 0 ]; then
-          echo "has_changes=true" >> "$GITHUB_OUTPUT"
-        fi
-
-  build-linux:
-    needs: check-changes
-    if: needs.check-changes.outputs.has_changes == 'true'
+  build-tarballs:
     strategy:
       matrix:
         include:
@@ -43,13 +28,13 @@ jobs:
 
     steps:
     - name: Checkout Repository
-      uses: actions/checkout@v7
+      uses: actions/checkout@v4
 
     - name: Install Podman
       run: sudo apt-get update && sudo apt-get install -y podman qemu-user-static
 
     - name: Login to GitHub Container Registry
-      uses: redhat-actions/podman-login@v2
+      uses: redhat-actions/podman-login@v1
       with:
         registry: ghcr.io
         username: ${{ github.repository_owner }}
@@ -59,28 +44,8 @@ jobs:
       run: ./dist.sh ${{ matrix.target }}
 
     - name: Upload artifact
-      uses: actions/upload-artifact@v7
+      uses: actions/upload-artifact@v4
       with:
         name: ${{ matrix.target }}
         path: dist/mold-*.tar.gz
         compression-level: 0
-
-  build-windows:
-    needs: check-changes
-    if: needs.check-changes.outputs.has_changes == 'true'
-    runs-on: windows-latest
-    steps:
-    - name: Checkout Repository
-      uses: actions/checkout@v7
-
-    - uses: dtolnay/rust-toolchain@stable
-
-    - name: Build and Archive
-      shell: pwsh
-      run: ./.github/workflows/build-windows.ps1
-
-    - name: Upload artifact
-      uses: actions/upload-artifact@v7
-      with:
-        name: win-x86_64
-        path: dist/mold-*.*

.github/workflows/build-native.yml

@@ -21,13 +21,13 @@ jobs:
 
     steps:
     - name: Checkout Repository
-      uses: actions/checkout@v7
+      uses: actions/checkout@v4
 
     - name: Install Podman
       run: sudo apt-get update && sudo apt-get install -y podman qemu-user-static
 
     - name: Login to GitHub Container Registry
-      uses: redhat-actions/podman-login@v2
+      uses: redhat-actions/podman-login@v1
       with:
         registry: ghcr.io
         username: ${{ github.repository_owner }}
@@ -37,7 +37,7 @@ jobs:
       run: ./dist.sh ${{ matrix.target }}
 
     - name: Upload artifact
-      uses: actions/upload-artifact@v7
+      uses: actions/upload-artifact@v4
       with:
         name: ${{ matrix.target }}
         path: dist/mold-*.tar.gz

.github/workflows/build-windows.ps1

@@ -1,16 +0,0 @@
-$ErrorActionPreference = 'Stop'
-Set-Location "$PSScriptRoot/../.."
-
-cargo build --release --locked --package mold-cli
-if ($LASTEXITCODE -ne 0) { exit $LASTEXITCODE }
-
-$metadata = cargo metadata --locked --no-deps --format-version 1 | ConvertFrom-Json
-if ($LASTEXITCODE -ne 0) { exit $LASTEXITCODE }
-$version = ($metadata.packages | Where-Object name -eq 'mold-cli').version
-
-$stage = 'mold-install'
-New-Item -ItemType Directory -Force "$stage/bin", "$stage/share/man/man1", "$stage/share/doc/mold", dist | Out-Null
-Copy-Item target/release/mold.exe "$stage/bin/"
-Copy-Item docs/mold.1 "$stage/share/man/man1/"
-Copy-Item LICENSE "$stage/share/doc/mold/"
-Compress-Archive -Path "$stage/*" -DestinationPath "dist/mold-$version-x86_64-windows.zip" -Force

.github/workflows/ci.yml

@@ -1,192 +1,149 @@
 name: CI
-
 on:
   push:
   pull_request:
-
+env:
+  UBSAN_OPTIONS: print_stacktrace=1:halt_on_error=1
 jobs:
-  test-all-targets:
-    runs-on: ubuntu-24.04
-    timeout-minutes: 60
-    env:
-      # Incremental artifacts and mold's own debug info are unused in CI.
-      CARGO_INCREMENTAL: 0
-      CARGO_PROFILE_DEV_DEBUG: 0
-    steps:
-    - uses: actions/checkout@v6
-    - uses: dtolnay/rust-toolchain@stable
-    - name: install test dependencies
-      run: |
-        sudo ./install-test-deps.sh
-        sudo .github/workflows/install-extras.sh
-    - run: cargo build --locked
-    - name: check the build for 32-bit hosts
-      run: |
-        rustup target add armv7-unknown-linux-gnueabihf i686-unknown-linux-gnu \
-          powerpc-unknown-linux-gnu
-        cargo check --locked --workspace --all-targets --target armv7-unknown-linux-gnueabihf
-        # i386 aligns 64-bit integers to 4 bytes
-        cargo check --locked --workspace --all-targets --target i686-unknown-linux-gnu
-        # 32-bit PowerPC has no 64-bit atomics
-        cargo check --locked --workspace --all-targets --target powerpc-unknown-linux-gnu
-    - name: verify all target toolchains are available
-      run: |
-        cargo test --locked -p mold-cli --test integration -- --list |
-          tee "$RUNNER_TEMP/test-inventory.txt"
-        ! grep -q '^unavailable:' "$RUNNER_TEMP/test-inventory.txt"
-    # All workspace crates were built above. Avoid linking empty test binaries
-    # for the target crates and command.
-    - run: cargo test --locked -p mold -p mold-tests -p mold-cli --lib --test integration
-    - name: archive test results
-      uses: actions/upload-artifact@v7
-      if: failure()
-      with:
-        name: test-results-all-targets
-        path: target/debug/mold-test/out/test
-
-  test-sanitizers:
+  build-sanitizers:
     strategy:
       matrix:
-        include:
-        - sanitizer: address
-          # Input files intentionally remain allocated until process exit.
-          runtime-options: detect_leaks=0:halt_on_error=1
-          test-prefix: ''
-          test-timeout: 30
-        - sanitizer: thread
-          runtime-options: halt_on_error=1
-          # TSan cannot model the atomic-fence synchronization in Rayon's
-          # work-stealing queue. Two CPUs still exercise parallel linker code.
-          test-prefix: taskset -c 0,1
-          test-timeout: 60
+        target:
+        - ''
+        - '-DMOLD_USE_ASAN=On'
+        - '-DMOLD_USE_TSAN=On'
     runs-on: ubuntu-24.04
-    timeout-minutes: 60
-    env:
-      CARGO_TARGET_DIR: target/${{ matrix.sanitizer }}
-      RUSTFLAGS: -Zsanitizer=${{ matrix.sanitizer }}
-      RUSTDOCFLAGS: -Zsanitizer=${{ matrix.sanitizer }}
     steps:
-    - uses: actions/checkout@v6
-    - uses: dtolnay/rust-toolchain@nightly
-      with:
-        components: rust-src
-    - run: sudo ./install-test-deps.sh
-    - run: cargo +nightly build --locked -Zbuild-std --target x86_64-unknown-linux-gnu -p mold-cli --no-default-features --features system-allocator,x86_64
-    - run: |
-        if [ '${{ matrix.sanitizer }}' = address ]; then
-          export ASAN_OPTIONS='${{ matrix.runtime-options }}'
-        else
-          export TSAN_OPTIONS='${{ matrix.runtime-options }}'
-        fi
-        ${{ matrix.test-prefix }} cargo +nightly test --locked -Zbuild-std --target x86_64-unknown-linux-gnu -p mold-cli --no-default-features --features system-allocator,x86_64 --test integration -- --native --test-threads 1 --timeout ${{ matrix.test-timeout }}
+    - uses: actions/checkout@v4
+    - uses: rui314/setup-mold@staging
+    - run: sudo ./install-build-deps.sh
+    - name: build
+      run: |
+        sudo apt-get install -y clang-18 clang gcc-multilib gdb dwarfdump zstd
+        mkdir build
+        cd build
+        cmake -DCMAKE_BUILD_TYPE=Debug -DCMAKE_C_COMPILER=clang-18 -DCMAKE_CXX_COMPILER=clang++-18 ${{ matrix.target }} ..
+        cmake --build . -j$(nproc)
+    - run: cd build; ctest --output-on-failure -j$(nproc)
     - name: archive test results
-      uses: actions/upload-artifact@v7
+      uses: actions/upload-artifact@v4
       if: failure()
       with:
-        name: test-results-${{ matrix.sanitizer }}
-        path: target/${{ matrix.sanitizer }}/x86_64-unknown-linux-gnu/debug/mold-test/out/test
+        name: test-results-clang
+        path: |
+          build
+          !build/CMakeFiles
 
-  build-msan:
+  build-multi-archs:
     runs-on: ubuntu-24.04
-    timeout-minutes: 60
     steps:
-    - uses: actions/checkout@v6
-    - uses: dtolnay/rust-toolchain@nightly
-      with:
-        components: rust-src
-    - run: sudo ./install-test-deps.sh
-    - run: sudo apt-get install -y clang llvm
-    - run: .github/workflows/run-msan.sh
+    - uses: actions/checkout@v4
+    - name: install-build-deps
+      run: |
+        sudo ./install-build-deps.sh
+        sudo ./install-cross-tools.sh
+        sudo .github/workflows/install-extras.sh
+    - name: build
+      run: |
+        mkdir build
+        cd build
+        cmake ..
+        cmake --build . -j$(nproc)
+    - run: cd build; ctest --output-on-failure -j$(nproc)
     - name: archive test results
-      uses: actions/upload-artifact@v7
+      uses: actions/upload-artifact@v4
       if: failure()
       with:
-        name: test-results-msan
-        path: target/msan/x86_64-unknown-linux-gnu/debug/mold-test/out/test
+        name: test-results-multi-archs
+        path: |
+          build
+          !build/CMakeFiles
 
-  test-distros:
+  build-distros:
     strategy:
       matrix:
         distro:
         - alpine
         - archlinux
-        - debian:12
+        - debian:11 # GCC 10 and CMake 3.18 - the minimum supported by mold
         - fedora
         - gentoo/stage3
         - opensuse/tumbleweed
         - ubuntu:22.04
         - ubuntu:25.04
     runs-on: ubuntu-latest
-    timeout-minutes: 60
-    # Tumbleweed does not declare PATH in its container configuration.
-    container:
-      image: ${{ matrix.distro }}
-      env:
-        PATH: /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+    container: ${{ matrix.distro }}
     steps:
-    - uses: actions/checkout@v6
-    - run: ./install-test-deps.sh
-    - uses: dtolnay/rust-toolchain@stable
-    - run: cargo build --locked -p mold-cli --no-default-features --features x86_64
-    - run: cargo test --locked -p mold-cli --no-default-features --features x86_64 --test integration -- --native
-    - name: sanitize distro name
-      if: failure()
-      id: sanitize
-      run: echo "name=$(echo '${{ matrix.distro }}' | tr '/:' '--')" >> "$GITHUB_OUTPUT"
+    - uses: actions/checkout@v4
+    - run: ./install-build-deps.sh
+    - name: build
+      run: |
+        mkdir build
+        cd build
+        cmake ..
+        cmake --build . -j$(nproc)
+    - run: cd build; ctest --output-on-failure -j$(nproc)
     - name: archive test results
-      uses: actions/upload-artifact@v7
+      uses: actions/upload-artifact@v4
       if: failure()
       with:
-        name: test-results-${{ steps.sanitize.outputs.name }}
-        path: target/debug/mold-test/out/test
+        name: test-results-${{ matrix.distro }}
+        path: |
+          build
+          !build/CMakeFiles
 
   build-macos:
     runs-on: macos-latest
-    timeout-minutes: 60
     steps:
-    - uses: actions/checkout@v6
-    - uses: dtolnay/rust-toolchain@stable
-    - run: cargo build --locked -p mold-cli --no-default-features --features x86_64
+    - uses: actions/checkout@v4
+    - name: build
+      run: |
+        mkdir build
+        cd build
+        cmake ..
+        cmake --build . -j$(sysctl -n hw.physicalcpu)
 
   build-windows:
     runs-on: windows-latest
-    timeout-minutes: 60
     steps:
-    - uses: actions/checkout@v6
-    - uses: dtolnay/rust-toolchain@stable
-    - run: cargo build --locked -p mold-cli --no-default-features --features x86_64
+    - uses: actions/checkout@v4
+    - name: build
+      run: |
+        mkdir build
+        cd build
+        cmake -T clangcl ..
+        cmake --build . -j $Env:NUMBER_OF_PROCESSORS
 
   build-msys:
     runs-on: windows-latest
-    timeout-minutes: 60
-    env:
-      CARGO_NET_GIT_FETCH_WITH_CLI: true
     steps:
-    - uses: actions/checkout@v6
-    - uses: msys2/setup-msys2@v2
+    - uses: actions/checkout@v4
+    - name: Setup MSYS2
+      uses: msys2/setup-msys2@v2
       with:
         msystem: UCRT64
         update: true
-        install: git
-        pacboy: rust:p cc:p dlfcn:p
-    - shell: msys2 {0}
-      run: cargo build --locked -p mold-cli --no-default-features --features x86_64
+        pacboy: gcc-libs:p libwinpthread-git:p tbb:p zlib:p zstd:p dlfcn:p cc:p cmake:p ninja:p
+    - name: build
+      shell: msys2 {0}
+      run: |
+        mkdir build
+        cd build
+        cmake -GNinja -DMOLD_USE_MIMALLOC=OFF -DMOLD_USE_SYSTEM_TBB=ON ..
+        cmake --build . -j $(nproc)
 
   build-freebsd:
     runs-on: ubuntu-latest
-    timeout-minutes: 60
-    env:
-      # The VM has little disk space, so omit unused build artifacts.
-      CARGO_INCREMENTAL: 0
-      CARGO_PROFILE_DEV_DEBUG: 0
-      CARGO_PROFILE_TEST_DEBUG: 0
     steps:
-    - uses: actions/checkout@v6
-    - uses: vmactions/freebsd-vm@v1
+    - uses: actions/checkout@v4
+    - name: Build and test
+      uses: vmactions/freebsd-vm@v1
       with:
         usesh: true
         run: |
-          pkg install -y rust
-          ./install-test-deps.sh
-          cargo build --locked -p mold-cli --no-default-features --features x86_64
-          cargo test --locked -p mold-cli --no-default-features --features x86_64 --test integration -- --native
+          ./install-build-deps.sh
+          mkdir build
+          cd build
+          cmake ..
+          cmake --build . -j$(nproc)
+          ctest --output-on-failure -j$(nproc)

.github/workflows/install-extras.sh

@@ -5,7 +5,7 @@ apt-get install -y wget xz-utils
 
 # Install a 32-bit RISC-V toolchain
 mkdir /rv32
-wget -O- --progress=dot:mega https://github.com/riscv-collab/riscv-gnu-toolchain/releases/download/2025.06.13/riscv32-glibc-ubuntu-24.04-gcc-nightly-2025.06.13-nightly.tar.xz | tar -C /rv32 --strip-components=1 --xz -xf -
+wget -O- -q https://github.com/riscv-collab/riscv-gnu-toolchain/releases/download/2025.01.20/riscv32-glibc-ubuntu-22.04-gcc-nightly-2025.01.20-nightly.tar.xz | tar -C /rv32 --strip-components=1 --xz -xf -
 
 ln -sf /rv32/sysroot /usr/riscv32-linux-gnu
 echo '/rv32/bin/riscv32-unknown-linux-gnu-gcc -L/usr/riscv32-linux-gnu "$@"' > /usr/bin/riscv32-linux-gnu-gcc
@@ -18,7 +18,7 @@ done
 
 # Install a LoongArch toolchain
 mkdir /larch
-wget -O- --progress=dot:mega https://github.com/loongson/build-tools/releases/download/2025.06.06/x86_64-cross-tools-loongarch64-binutils_2.44-gcc_15.1.0-glibc_2.41.tar.xz | tar -C /larch --strip-components=1 --xz -xf -
+wget -O- -q https://github.com/loongson/build-tools/releases/download/2025.02.21/x86_64-cross-tools-loongarch64-binutils_2.44-gcc_14.2.0-glibc_2.41.tar.xz | tar -C /larch --strip-components=1 --xz -xf -
 
 cp -r /larch/loongarch64-unknown-linux-gnu/lib/* /larch/target/lib64
 ln -sf /larch/target /usr/loongarch64-linux-gnu
@@ -27,39 +27,25 @@ for i in gcc g++ objdump objcopy strip; do
   ln -sf /larch/bin/loongarch64-unknown-linux-gnu-$i /usr/bin/loongarch64-linux-gnu-$i
 done
 
-wget -O /usr/local/bin/qemu-loongarch64 --progress=dot:mega https://github.com/loongson/build-tools/releases/download/2025.06.06/qemu-loongarch64
+wget -O /usr/local/bin/qemu-loongarch64 -q https://github.com/loongson/build-tools/releases/download/2024.11.01/qemu-loongarch64
 chmod 755 /usr/local/bin/qemu-loongarch64
 
-# Install ARM32 big-endian toolchain
-mkdir /armeb
-wget -O- --progress=dot:mega https://toolchains.bootlin.com/downloads/releases/toolchains/armebv7-eabihf/tarballs/armebv7-eabihf--glibc--stable-2024.05-1.tar.xz | tar -C /armeb --strip-components=1 --xz -xf -
-
-ln -sf /armeb/armeb-buildroot-linux-gnueabihf/sysroot /usr/armeb-linux-gnueabihf
-echo '/armeb/bin/armeb-linux-gcc -L/usr/armeb-linux-gnu "$@"' > /usr/bin/armeb-linux-gnueabihf-gcc
-echo '/armeb/bin/armeb-linux-g++ -L/usr/armeb-linux-gnu "$@"' > /usr/bin/armeb-linux-gnueabihf-g++
-chmod 755 /usr/bin/armeb-linux-gnueabihf-{gcc,g++}
-
-for i in objdump objcopy strip; do
-  ln -sf /armeb/bin/armeb-linux-$i /usr/bin/armeb-linux-gnueabihf-$i
-done
-
 # Install ARM64 big-endian toolchain
 mkdir /aarch64be
-wget -O- --progress=dot:mega https://toolchains.bootlin.com/downloads/releases/toolchains/aarch64be/tarballs/aarch64be--glibc--stable-2024.05-1.tar.xz | tar -C /aarch64be --strip-components=1 --xz -xf -
+wget -O- -q https://sources.buildroot.net/toolchain-external-arm-aarch64-be/arm-gnu-toolchain-13.3.rel1-x86_64-aarch64_be-none-linux-gnu.tar.xz | tar -C /aarch64be --strip-components=1 --xz -xf -
 
-ln -sf /aarch64be/aarch64_be-buildroot-linux-gnu/sysroot /usr/aarch64_be-linux-gnu
-echo '/aarch64be/bin/aarch64_be-linux-gcc -L/usr/aarch64_be-linux-gnu "$@"' > /usr/bin/aarch64_be-linux-gnu-gcc
-echo '/aarch64be/bin/aarch64_be-linux-g++ -L/usr/aarch64_be-linux-gnu "$@"' > /usr/bin/aarch64_be-linux-gnu-g++
+ln -sf /aarch64be/aarch64_be-none-linux-gnu/libc /usr/aarch64_be-linux-gnu
+echo '/aarch64be/bin/aarch64_be-none-linux-gnu-gcc -L/usr/aarch64_be-linux-gnu "$@"' > /usr/bin/aarch64_be-linux-gnu-gcc
+echo '/aarch64be/bin/aarch64_be-none-linux-gnu-g++ -L/usr/aarch64_be-linux-gnu "$@"' > /usr/bin/aarch64_be-linux-gnu-g++
 chmod 755 /usr/bin/aarch64_be-linux-gnu-{gcc,g++}
 
 for i in objdump objcopy strip; do
-  ln -sf /aarch64be/bin/aarch64_be-linux-$i /usr/bin/aarch64_be-linux-gnu-$i
+  ln -sf /aarch64be/bin/aarch64_be-none-linux-gnu-$i /usr/bin/aarch64_be-linux-gnu-$i
 done
 
 # Install SH4 big-endian toolchain
 mkdir /sh4aeb
-wget -O- --progress=dot:mega https://toolchains.bootlin.com/downloads/releases/toolchains/sh-sh4aeb/tarballs/sh-sh4aeb--glibc--stable-2024.05-1.tar.xz | tar -C /sh4aeb --strip-components=1 --xz -xf -
-
+wget -O- -q https://toolchains.bootlin.com/downloads/releases/toolchains/sh-sh4aeb/tarballs/sh-sh4aeb--glibc--stable-2024.05-1.tar.xz | tar -C /sh4aeb --strip-components=1 --xz -xf -
 ln -sf /sh4aeb/sh4aeb-buildroot-linux-gnu/sysroot /usr/sh4aeb-linux-gnu
 echo '/sh4aeb/bin/sh4aeb-linux-gcc -L/usr/sh4aeb-linux-gnu "$@"' > /usr/bin/sh4aeb-linux-gnu-gcc
 echo '/sh4aeb/bin/sh4aeb-linux-g++ -L/usr/sh4aeb-linux-gnu "$@"' > /usr/bin/sh4aeb-linux-gnu-g++
@@ -71,5 +57,5 @@ done
 
 # Install Intel SDE CPU emulator for CET-related tests
 mkdir /sde
-wget -O- --progress=dot:mega https://downloadmirror.intel.com/850782/sde-external-9.53.0-2025-03-16-lin.tar.xz | tar -C /sde --strip-components=1 --xz -xf -
+wget -O- -q https://downloadmirror.intel.com/843185/sde-external-9.48.0-2024-11-25-lin.tar.xz | tar -C /sde --strip-components=1 --xz -xf -
 ln -s /sde/sde64 /usr/bin

.github/workflows/release-assets.yml

@@ -1,97 +0,0 @@
-name: Build & attach tarballs on tag push
-
-on:
-  push:
-    tags: ['v[0-9]*']
-
-permissions:
-  contents: write
-  packages: write
-  id-token: write
-
-env:
-  TAG: ${{ github.ref_name }}
-
-jobs:
-  build-linux:
-    strategy:
-      matrix:
-        include:
-        - { target: x86_64,      os: ubuntu-24.04 }
-        - { target: aarch64,     os: ubuntu-24.04-arm }
-        - { target: arm,         os: ubuntu-24.04-arm }
-        - { target: riscv64,     os: ubuntu-24.04 }
-        - { target: ppc64le,     os: ubuntu-24.04 }
-        - { target: s390x,       os: ubuntu-24.04 }
-        - { target: loongarch64, os: ubuntu-24.04 }
-
-    runs-on: ${{ matrix.os }}
-
-    steps:
-    - uses: actions/checkout@v7
-
-    - name: Install Podman
-      run: sudo apt-get update && sudo apt-get install -y podman qemu-user-static
-
-    - name: Login to GitHub Container Registry
-      uses: redhat-actions/podman-login@v2
-      with:
-        registry: ghcr.io
-        username: ${{ github.repository_owner }}
-        password: ${{ secrets.GITHUB_TOKEN }}
-
-    - run: ./dist.sh ${{ matrix.target }}
-
-    - uses: actions/upload-artifact@v7
-      with:
-        name: ${{ matrix.target }}
-        path: dist/mold-*.tar.gz
-
-  build-windows:
-    runs-on: windows-latest
-    steps:
-    - uses: actions/checkout@v7
-
-    - uses: dtolnay/rust-toolchain@stable
-
-    - name: Build and Archive
-      shell: pwsh
-      run: ./.github/workflows/build-windows.ps1
-
-    - uses: actions/upload-artifact@v7
-      with:
-        name: win-x86_64
-        path: dist/mold-*.*
-
-  publish:
-    needs: [build-linux, build-windows]
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@v7
-
-    - uses: actions/download-artifact@v8
-      with:
-        path: dist
-        pattern: '*'
-        merge-multiple: true
-
-    - name: Ensure release exists (create if missing)
-      env:
-        GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-      run: |
-        set -e
-        if gh release view "$TAG" >& /dev/null; then
-          echo "Existing release found for $TAG"
-        else
-          echo "Creating draft release for $TAG"
-          gh release create "$TAG" --draft \
-            --title "$TAG" \
-            --notes "Automated draft – fill the changelog later."
-        fi
-
-    - name: Upload tarballs
-      env:
-        GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-      run: |
-        gh release upload "$TAG" dist/* --clobber
-        gh release view "$TAG" --json assets --jq '.assets[].name'

.github/workflows/run-msan.sh

@@ -1,34 +0,0 @@
-#!/bin/bash
-set -euo pipefail
-cd "$(dirname "$0")/../.."
-
-# MSan requires instrumented Rust, std, and native dependencies:
-# https://doc.rust-lang.org/unstable-book/compiler-flags/sanitizer.html#memorysanitizer
-export CARGO_TARGET_DIR="${CARGO_TARGET_DIR:-target/msan}"
-export RUSTFLAGS='-Zsanitizer=memory -Zsanitizer-memory-track-origins=2'
-export RUSTDOCFLAGS="$RUSTFLAGS"
-export CC_x86_64_unknown_linux_gnu=clang
-export CFLAGS_x86_64_unknown_linux_gnu='-fsanitize=memory -fsanitize-memory-track-origins=2 -fno-omit-frame-pointer'
-export LIBZ_SYS_STATIC=1
-export MSAN_OPTIONS=halt_on_error=1
-
-# The instrumented linker is too slow unoptimized for the heaviest tests
-# to finish within the per-test timeout.
-export CARGO_PROFILE_DEV_OPT_LEVEL=1
-
-# Use instrumentable implementations instead of BLAKE3/Zstd assembly, and
-# select mold as well as mold-cli so Cargo enables its dependency features.
-args=(
-  --locked -Zbuild-std --target x86_64-unknown-linux-gnu
-  --package mold --package mold-cli --no-default-features
-  --features mold-cli/system-allocator,mold-cli/x86_64,blake3/pure,zstd/no_asm
-  --test integration
-)
-cargo +nightly test "${args[@]}" --no-run
-
-# The preload wrapper runs inside uninstrumented compiler processes, not
-# inside mold. Rebuild it without MSan so those processes can load it.
-clang -shared -fPIC -o "$CARGO_TARGET_DIR/x86_64-unknown-linux-gnu/debug/mold-wrapper.so" \
-  c/mold-wrapper.c -ldl
-
-cargo +nightly test "${args[@]}" -- --native --test-threads 1 --timeout 60 "$@"

.github/workflows/update-manpage.yml

@@ -8,16 +8,13 @@ on:
       - main
   workflow_dispatch:
 
-permissions:
-  contents: write
-
 jobs:
   update-manpage:
     runs-on: ubuntu-latest
 
     steps:
     - name: Check out repository
-      uses: actions/checkout@v7
+      uses: actions/checkout@v4
 
     - name: Install ronn
       run: sudo apt-get update && sudo apt-get install -y ronn

.gitignore

@@ -1,6 +1,11 @@
-/target
-/dist
-/bench
-/.claude
-/.codex
+*.o
+*.so
 *~
+**/.DS_Store
+.cache
+core
+gentoo
+/mold-*.tar.gz
+/build*
+/mold
+/dist

CMakeLists.txt

@@ -0,0 +1,458 @@
+# You can customize a build by specifying CMake options. An option may be
+# given in the -Dvariable=value form. For a boolean variable, `ON` or `1`
+# means true, while `OFF` or `0` means false.
+#
+# Here are a couple of common cmake options:
+#
+#  -DCMAKE_C_COMPILER=<command-name>
+#
+#   Specifies the C compiler name to use. The default value is `cc`.
+#
+#  -DCMAKE_CXX_COMPILER=<command-name>
+#
+#   Specifies the C++ compiler name to use. The default value is `c++`.
+#
+#  -DCMAKE_INSTALL_PREFIX=<directory>
+#
+#   Specifies the install target directory. The default value is `/usr/local`.
+#
+#  -DCMAKE_BUILD_TYPE=[Debug | Release | RelWithDebInfo | MinSizeRel]
+#
+#   Specifies the build type. The default is `Release`, which is the right
+#   option unless you are debugging mold.
+#
+# An example of a cmake command line is shown below:
+#
+#   $ cmake -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_CXX_COMPILER=g++-12 ..
+#
+# where `..` refers to this directory.
+#
+# With cmake, you may run `cmake --install .` instead of `make install` to
+# install build artifacts to system directories. If you want to install
+# artifacts to a temporary target directory, run `cmake --install . --prefix
+# <dir>`.
+#
+# You can see the current cmake variables and their values by running
+# `cmake -N -L .` in a build directory.
+#
+# Note that in this file, we provide various dials and knobs to configure
+# how to build mold. However, as a policy, we do not provide a way to
+# enable/disable any individual mold's feature. In other words, we do not
+# provide options like `--enable-foo` or `--disable-foo`. The motivation
+# behind this is build reproducibility. We want to guarantee that all builds
+# of the mold linker of the same version will have the exact same set of
+# features and behave exactly the same.
+
+cmake_minimum_required(VERSION 3.14)
+project(mold VERSION 2.37.1)
+
+include(CMakeDependentOption)
+include(CheckSymbolExists)
+include(GNUInstallDirs)
+
+add_executable(mold)
+target_compile_features(mold PRIVATE cxx_std_20)
+
+if(MINGW)
+  target_link_libraries(mold PRIVATE dl)
+else()
+  target_link_libraries(mold PRIVATE ${CMAKE_DL_LIBS})
+endif()
+
+# Build mold itself using mold if -DMOLD_USE_MOLD=ON
+option(MOLD_USE_MOLD "Use mold to build mold" OFF)
+if(MOLD_USE_MOLD)
+  target_link_options(mold PRIVATE -fuse-ld=mold -Wl,--gdb-index)
+
+  if(CMAKE_BUILD_TYPE MATCHES "^Rel")
+    target_link_options(mold PRIVATE -Wl,--gc-sections,--icf=safe)
+  endif()
+endif()
+
+if(NOT "${CMAKE_CXX_COMPILER_FRONTEND_VARIANT}" STREQUAL "MSVC")
+  target_compile_options(mold PRIVATE
+    -fno-exceptions
+    -fno-unwind-tables
+    -fno-asynchronous-unwind-tables
+    -ffunction-sections
+    -fdata-sections
+    -Wall
+    -Wextra
+    -Wno-sign-compare
+    -Wno-unused-function
+    -Wno-unused-parameter
+    -Wno-missing-field-initializers
+    -ggnu-pubnames)
+endif()
+
+if(CMAKE_BUILD_TYPE STREQUAL "Debug")
+  target_compile_options(mold PRIVATE -D_GLIBCXX_ASSERTIONS)
+endif()
+
+if(CMAKE_SYSTEM_NAME STREQUAL "OpenBSD")
+  set(OPENBSD ON)
+endif()
+
+# Build mold with -flto if -DMOLD_LTO=ON
+option(MOLD_LTO "Build mold with link-time optimization enabled")
+if(MOLD_LTO)
+  set_property(TARGET mold PROPERTY INTERPROCEDURAL_OPTIMIZATION ON)
+endif()
+
+# Enable AddressSanitizer if -DMOLD_USE_ASAN=ON
+option(MOLD_USE_ASAN "Build mold with AddressSanitizer" OFF)
+if(MOLD_USE_ASAN)
+  target_compile_options(mold PRIVATE -fsanitize=address -fsanitize=undefined)
+  target_link_options(mold PRIVATE -fsanitize=address -fsanitize=undefined)
+endif()
+
+# Enabled ThreadSanitizer if -DMOLD_USE_TSAN=ON
+option(MOLD_USE_TSAN "Build mold with ThreadSanitizer" OFF)
+if(MOLD_USE_TSAN)
+  target_compile_options(mold PRIVATE -fsanitize=thread)
+  target_link_options(mold PRIVATE -fsanitize=thread)
+endif()
+
+# Statically-link libstdc++ if -DMOLD_MOSTLY_STATIC=ON.
+#
+# This option is intended to be used by `./dist.sh` script to create a
+# mold binary that works on various Linux distros. You probably don't
+# need nor want to set this to ON.
+option(MOLD_MOSTLY_STATIC "Statically link libstdc++ and some other libraries" OFF)
+if(MOLD_MOSTLY_STATIC)
+  target_link_options(mold PRIVATE -static-libstdc++)
+endif()
+
+# Find zlib. If libz.so is not found, we compile a bundled one and
+# statically-link it to mold.
+find_package(ZLIB QUIET)
+if(ZLIB_FOUND AND NOT MOLD_MOSTLY_STATIC)
+  target_link_libraries(mold PRIVATE ZLIB::ZLIB)
+else()
+  set(ZLIB_BUILD_EXAMPLES OFF CACHE INTERNAL "")
+  add_subdirectory(third-party/zlib EXCLUDE_FROM_ALL)
+  target_include_directories(zlibstatic INTERFACE third-party/zlib
+    $<TARGET_PROPERTY:zlibstatic,BINARY_DIR>)
+  target_link_libraries(mold PRIVATE zlibstatic)
+endif()
+
+# Find BLAKE3 cryptographic hash library. Just like zlib, if libblkae3.so
+# is not found, we compile a bundled one and statically-link it to mold.
+find_package(BLAKE3 QUIET)
+if(BLAKE3_FOUND AND NOT MOLD_MOSTLY_STATIC)
+  target_link_libraries(mold PRIVATE BLAKE3::blake3)
+else()
+  function(mold_add_blake3)
+    set(BUILD_SHARED_LIBS OFF)
+    add_subdirectory(third-party/blake3/c EXCLUDE_FROM_ALL)
+    target_link_libraries(mold PRIVATE blake3)
+    target_include_directories(mold PUBLIC third-party/blake3/c)
+  endfunction()
+
+  mold_add_blake3()
+endif()
+
+# Find zstd compression library. If zstd.h is not found, we compile a
+# bundled one and statically-link it to mold.
+include(CheckIncludeFile)
+check_include_file(zstd.h HAVE_ZSTD_H)
+
+if(HAVE_ZSTD_H AND NOT MOLD_MOSTLY_STATIC)
+  target_link_libraries(mold PRIVATE zstd)
+else()
+  add_subdirectory(third-party/zstd/build/cmake EXCLUDE_FROM_ALL)
+  target_compile_definitions(libzstd_static PRIVATE
+    ZSTD_BUILD_STATIC=1
+    ZSTD_BUILD_SHARED=0
+    ZSTD_BUILD_PROGRAMS=0
+    ZSTD_MULTITHREAD_SUPPORT=0
+    ZSTD_BUILD_TESTS=0)
+  target_include_directories(mold PUBLIC third-party/zstd/lib)
+  target_link_libraries(mold PRIVATE libzstd_static)
+endif()
+
+# Find mimalloc. mimalloc is an alternative malloc implementation
+# optimized for multi-threaded applications.
+#
+# If you want to use the usual libc's malloc, pass -DMOLD_USE_MIMALLOC=OFF.
+#
+# We enable mimalloc by default for 64-bit targets. It doesn't seem to
+# be stable on 32-bit targets.
+cmake_dependent_option(
+  MOLD_USE_MIMALLOC "Use mimalloc" ON
+  "CMAKE_SIZEOF_VOID_P EQUAL 8; NOT APPLE; NOT ANDROID; NOT OPENBSD; NOT MOLD_USE_ASAN; NOT MOLD_USE_TSAN" OFF)
+
+cmake_dependent_option(
+  MOLD_USE_SYSTEM_MIMALLOC "Use system or vendored mimalloc" OFF
+  MOLD_USE_MIMALLOC OFF)
+
+# By default, we build a bundled mimalloc and statically-link it to
+# mold. If you want to dynamically link to the system's
+# libmimalloc.so, pass -DMOLD_USE_SYSTEM_MIMALLOC=ON.
+if(MOLD_USE_MIMALLOC)
+  if(MOLD_USE_SYSTEM_MIMALLOC)
+    find_package(mimalloc REQUIRED)
+    target_link_libraries(mold PRIVATE mimalloc)
+  else()
+    function(mold_add_mimalloc)
+      set(MI_BUILD_STATIC ON CACHE INTERNAL "")
+      set(MI_BUILD_TESTS OFF CACHE INTERNAL "")
+      add_subdirectory(third-party/mimalloc EXCLUDE_FROM_ALL)
+      target_compile_definitions(mimalloc-static PRIVATE MI_USE_ENVIRON=0)
+      target_link_libraries(mold PRIVATE mimalloc-static)
+    endfunction()
+
+    mold_add_mimalloc()
+  endif()
+endif()
+
+# Find TBB. TBB (OneTBB or Intel TBB) is a high-level threading library.
+# Use of this library is mandatory.
+#
+# By default, we build a bundled one and statically-link the library
+# to mold. If you want to link to the system's libtbb2.so, pass
+# -DMOLD_USE_SYSTEM_TBB=ON.
+option(MOLD_USE_SYSTEM_TBB "Use system or vendored TBB" OFF)
+if(MOLD_USE_SYSTEM_TBB)
+  find_package(TBB REQUIRED)
+  target_link_libraries(mold PRIVATE TBB::tbb)
+else()
+  function(mold_add_tbb)
+    set(BUILD_SHARED_LIBS OFF)
+    set(TBB_TEST OFF CACHE INTERNAL "")
+    set(TBB_STRICT OFF CACHE INTERNAL "")
+    add_subdirectory(third-party/tbb EXCLUDE_FROM_ALL)
+    target_compile_definitions(tbb PRIVATE __TBB_DYNAMIC_LOAD_ENABLED=0)
+    target_link_libraries(mold PRIVATE TBB::tbb)
+  endfunction()
+
+  mold_add_tbb()
+endif()
+
+# We always use Clang to build mold on Windows. MSVC can't compile mold.
+if(WIN32)
+  if(MSVC AND NOT CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+    message(FATAL_ERROR
+      "Your compiler is not supported; install Clang from Visual Studio Installer and re-run cmake with '-T clangcl'")
+  endif()
+
+  target_compile_definitions(mold PRIVATE NOGDI NOMINMAX)
+  if(MINGW)
+    target_compile_definitions(mold PRIVATE _WIN32_WINNT=0xA00)
+    target_link_libraries(mold PRIVATE bcrypt)
+  endif()
+else()
+  include(CheckLibraryExists)
+  check_library_exists(m pow "" LIBM_FOUND)
+  if(LIBM_FOUND)
+    target_link_libraries(mold PRIVATE m)
+  endif()
+endif()
+
+# Build mold-wrapper.so
+if(NOT APPLE AND NOT WIN32)
+  add_library(mold-wrapper SHARED)
+  install(TARGETS mold-wrapper DESTINATION ${CMAKE_INSTALL_LIBDIR}/mold)
+
+  # Remove the default `lib` prefix
+  set_target_properties(mold-wrapper PROPERTIES PREFIX "")
+  target_link_libraries(mold-wrapper PRIVATE ${CMAKE_DL_LIBS})
+  target_sources(mold-wrapper PRIVATE src/mold-wrapper.c)
+endif()
+
+# If atomics doesn't work by default, add -latomic.
+# We need the flag on riscv, armv6 and m68k.
+include(CheckCXXSourceCompiles)
+check_cxx_source_compiles("#include <atomic>
+int main() {
+  std::atomic_uint8_t  a;
+  std::atomic_uint16_t b;
+  std::atomic_uint32_t c;
+  std::atomic_uint64_t d;
+  return ++a + ++b + ++c + ++d;
+}" HAVE_FULL_ATOMIC_SUPPORT)
+
+if(NOT HAVE_FULL_ATOMIC_SUPPORT)
+  target_link_libraries(mold PRIVATE atomic)
+endif()
+
+# Add -pthread
+if(NOT APPLE AND NOT MSVC)
+  target_compile_options(mold PRIVATE -pthread)
+  target_link_options(mold PRIVATE -pthread)
+endif()
+
+check_symbol_exists(madvise sys/mman.h HAVE_MADVISE)
+check_symbol_exists(uname sys/utsname.h HAVE_UNAME)
+
+# Create a .cc file containing the current git hash for `mold --version`.
+add_custom_target(git_hash
+  COMMAND ${CMAKE_COMMAND}
+    -DSOURCE_DIR=${CMAKE_SOURCE_DIR}
+    -DOUTPUT_FILE=${CMAKE_BINARY_DIR}/git-hash.cc
+    -P ${CMAKE_SOURCE_DIR}/lib/update-git-hash.cmake
+  DEPENDS lib/update-git-hash.cmake
+  BYPRODUCTS git-hash.cc
+  VERBATIM)
+
+add_dependencies(mold git_hash)
+
+# Create config.h file
+configure_file(lib/config.h.in config.h)
+include_directories(${CMAKE_CURRENT_BINARY_DIR})
+
+# Almost all functions are template in mold which take a target type
+# (e.g. X86_64) as its type parameter. Since we suport more than 10
+# targets, compiling a single source file for all the targets is very
+# slow.
+#
+# As a workaround, we create a .cc file for each target and spawn many
+# compiler instances. This is hacky but greatly reduces compile time
+# on a multicore machine.
+list(APPEND MOLD_ELF_TARGETS
+  X86_64 I386 ARM64LE ARM64BE ARM32 RV32LE RV32BE RV64LE RV64BE PPC32
+  PPC64V1 PPC64V2 S390X SPARC64 M68K SH4LE SH4BE LOONGARCH32 LOONGARCH64 ARC)
+
+list(APPEND MOLD_ELF_TEMPLATE_FILES
+  src/arch-arm64.cc
+  src/arch-loongarch.cc
+  src/arch-riscv.cc
+  src/arch-sh4.cc
+  src/cmdline.cc
+  src/filetype.cc
+  src/gc-sections.cc
+  src/gdb-index.cc
+  src/icf.cc
+  src/input-files.cc
+  src/input-sections.cc
+  src/linker-script.cc
+  src/main.cc
+  src/mapfile.cc
+  src/output-chunks.cc
+  src/passes.cc
+  src/relocatable.cc
+  src/shrink-sections.cc
+  src/thunks.cc
+  src/tls.cc
+  )
+
+if(WIN32 AND NOT MINGW)
+  list(APPEND MOLD_ELF_TEMPLATE_FILES src/lto-win32.cc)
+else()
+  list(APPEND MOLD_ELF_TEMPLATE_FILES src/lto-unix.cc)
+endif()
+
+if(WIN32)
+  list(APPEND MOLD_ELF_TEMPLATE_FILES
+    src/output-file-win32.cc
+    src/subprocess-win32.cc
+    )
+else()
+  list(APPEND MOLD_ELF_TEMPLATE_FILES
+    src/output-file-unix.cc
+    src/subprocess-unix.cc
+  )
+endif()
+
+function(mold_instantiate_templates SOURCE TARGET)
+  set(PATH ${CMAKE_BINARY_DIR}/${SOURCE}.${TARGET}.cc)
+  if(NOT EXISTS ${PATH})
+    file(WRITE ${PATH} "#define MOLD_${TARGET} 1
+#define MOLD_TARGET ${TARGET}
+#include \"${CMAKE_SOURCE_DIR}/${SOURCE}\"
+")
+  endif()
+  target_sources(mold PRIVATE ${PATH})
+endfunction()
+
+foreach (SOURCE IN LISTS MOLD_ELF_TEMPLATE_FILES)
+  foreach(TARGET IN LISTS MOLD_ELF_TARGETS)
+    mold_instantiate_templates(${SOURCE} ${TARGET})
+  endforeach()
+endforeach()
+
+# Add other non-template source files.
+target_sources(mold PRIVATE
+  git-hash.cc
+  lib/compress.cc
+  lib/crc32.cc
+  lib/demangle.cc
+  lib/filepath.cc
+  lib/glob.cc
+  lib/hyperloglog.cc
+  lib/mimalloc.cc
+  lib/multi-glob.cc
+  lib/perf.cc
+  lib/random.cc
+  lib/tar.cc
+  src/arch-arc.cc
+  src/arch-arm32.cc
+  src/arch-i386.cc
+  src/arch-m68k.cc
+  src/arch-ppc32.cc
+  src/arch-ppc64v1.cc
+  src/arch-ppc64v2.cc
+  src/arch-s390x.cc
+  src/arch-sparc64.cc
+  src/arch-x86-64.cc
+  src/config.cc
+  src/elf.cc
+  third-party/rust-demangle/rust-demangle.c
+  )
+
+if(WIN32)
+  target_sources(mold PRIVATE
+    lib/jobs-win32.cc
+    lib/mapped-file-win32.cc
+    lib/signal-win32.cc
+    )
+else()
+  target_sources(mold PRIVATE
+    lib/jobs-unix.cc
+    lib/mapped-file-unix.cc
+    lib/signal-unix.cc
+    )
+endif()
+
+include(CTest)
+
+if(BUILD_TESTING)
+  # Create the ld symlinks required for testing
+  if(NOT WIN32)
+    add_custom_command(
+      TARGET mold POST_BUILD
+      COMMAND ${CMAKE_COMMAND} -E create_symlink mold ld
+      BYPRODUCTS ld
+      WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+      VERBATIM)
+  endif()
+
+  if(${UNIX})
+    add_subdirectory(test)
+  endif()
+endif()
+
+if(NOT CMAKE_SKIP_INSTALL_RULES)
+  install(TARGETS mold RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR})
+  install(FILES docs/mold.1 DESTINATION ${CMAKE_INSTALL_MANDIR}/man1/)
+  install(FILES LICENSE DESTINATION ${CMAKE_INSTALL_DOCDIR})
+
+  function(mold_install_relative_symlink OLD NEW)
+    install(CODE "
+      get_filename_component(PREFIX_ABS \${CMAKE_INSTALL_PREFIX}/ ABSOLUTE)
+      get_filename_component(OLD_ABS ${OLD} ABSOLUTE BASE_DIR \${PREFIX_ABS})
+      get_filename_component(NEW_ABS ${NEW} ABSOLUTE BASE_DIR \${PREFIX_ABS})
+      get_filename_component(NEW_DIR \${NEW_ABS} DIRECTORY)
+      file(RELATIVE_PATH OLD_REL \${NEW_DIR} \${OLD_ABS})
+      message(STATUS \"Installing symlink: \$ENV{DESTDIR}\${NEW_ABS} -> \${OLD_REL}\")
+      file(MAKE_DIRECTORY \$ENV{DESTDIR}\${NEW_DIR})
+      file(CREATE_LINK \${OLD_REL} \$ENV{DESTDIR}\${NEW_ABS} SYMBOLIC)")
+  endfunction()
+
+  mold_install_relative_symlink(${CMAKE_INSTALL_BINDIR}/mold${CMAKE_EXECUTABLE_SUFFIX}
+    ${CMAKE_INSTALL_LIBEXECDIR}/mold/ld${CMAKE_EXECUTABLE_SUFFIX})
+  mold_install_relative_symlink(${CMAKE_INSTALL_BINDIR}/mold${CMAKE_EXECUTABLE_SUFFIX}
+    ${CMAKE_INSTALL_BINDIR}/ld.mold${CMAKE_EXECUTABLE_SUFFIX})
+  mold_install_relative_symlink(${CMAKE_INSTALL_MANDIR}/man1/mold.1
+    ${CMAKE_INSTALL_MANDIR}/man1/ld.mold.1)
+endif()

Cargo.lock

@@ -1,590 +0,0 @@
-# This file is automatically @generated by Cargo.
-# It is not intended for manual editing.
-version = 4
-
-[[package]]
-name = "allocator-api2"
-version = "0.2.21"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "683d7910e743518b0e34f1186f92494becacb047c7b6bf616c96772180fef923"
-
-[[package]]
-name = "arrayvec"
-version = "0.7.8"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d3fb67a6e08acf24fdeccbac2cb6ac4305825bd1f117462e0e6f2f193345ad56"
-
-[[package]]
-name = "blake3"
-version = "1.8.7"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6d9e454fc11f76977dc803893aff6304ed33d6a26efae8696573bea74baa27ae"
-dependencies = [
- "arrayvec",
- "cc",
- "cfg-if",
- "constant_time_eq",
- "cpufeatures",
-]
-
-[[package]]
-name = "bstr"
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Cargo.toml

@@ -1,53 +0,0 @@
-[package]
-name = "mold"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "A high-performance ELF linker, rewritten in Rust"
-license.workspace = true
-# tests/lib.rs belongs to the mold-tests workspace crate.
-autotests = false
-
-# The linker is generic over the target. Instantiating it for all twenty
-# targets in one crate keeps the compiler on a single core for minutes, so
-# each target is instantiated in a crate of its own under arch/, and the
-# executable in cli/ dispatches to them.
-[workspace]
-members = ["cli", "arch/*", "tests"]
-default-members = [".", "cli", "arch/*", "tests"]
-
-[workspace.package]
-version = "3.0.0"
-edition = "2024"
-rust-version = "1.95"
-license = "MIT"
-
-[workspace.dependencies]
-libc = "0.2"
-mold = { path = "." }
-
-[dependencies]
-blake3 = "1.8.7"
-bstr = "1"
-cpp_demangle = "0.4"
-crc32fast = "1"
-flate2 = { version = "1", default-features = false, features = ["zlib"] }
-getrandom = "0.4.3"
-hashbrown = "0.17.1"
-libc.workspace = true
-libz-sys = "1.1.29"
-memchr = "2.8.3"
-memmap2 = "0.9"
-# std has no 64-bit atomics on hosts such as 32-bit PowerPC.
-portable-atomic = "1"
-rayon = "1"
-rustc-demangle = "0.1"
-uuid = { version = "1.27", default-features = false, features = ["v4"] }
-xxhash-rust = { version = "0.8", features = ["xxh3"] }
-zstd = "0.13"
-
-[build-dependencies]
-cc = "1"
-
-[profile.release]
-panic = "abort"

README.md

@@ -1,21 +1,30 @@
 # mold: A Modern Linker
 
-mold is a high-performance drop-in replacement for existing Unix linkers,
-designed to speed up builds. In our August 2026 benchmarks, it links 4.9x
-faster than [LLVM lld](https://lld.llvm.org) and 1.9x faster than
-[wild](https://github.com/wild-linker/wild) at the median; see
-[Benchmark](#benchmark) for the full results.
+mold is a faster drop-in replacement for existing Unix linkers. It is several
+times quicker than the LLVM lld linker, the second-fastest open-source linker,
+which I initially developed a few years ago. mold aims to enhance developer
+productivity by minimizing build time, particularly in rapid
+debug-edit-rebuild cycles.
 
-mold is written by the original developer of LLVM lld, the linker that
-Android, Chrome, FreeBSD, PlayStation, Nintendo Switch, and other production
-systems are built with. mold started as an effort to build an even faster
-linker from scratch, free of the architectural limits its author had run into
-while optimizing lld. It has been in production use since 2021, and today it
-is the default linker of many large open-source projects and is used
-internally by many companies.
+Here is a performance comparison of GNU ld, GNU gold, LLVM lld, and
+mold when linking final debuginfo-enabled executables for major large
+programs on a simulated 16-core, 32-thread machine.
 
-mold supports x86-64, i386, ARM 32/64, RISC-V 32/64, PowerPC 32/64, s390x,
-LoongArch 32/64, SPARC64, m68k, and SH-4.
+![Link speed comparison](docs/chart.svg)
+
+| Program (linker output size)  | GNU ld | GNU gold | LLVM lld | mold
+|-------------------------------|--------|----------|----------|------
+| MySQL 8.3 (0.47 GiB)          | 10.84s | 7.47s    | 1.64s    | 0.46s
+| Clang 19 (1.56 GiB)           | 42.07s | 33.13s   | 5.20s    | 1.35s
+| Chromium 124 (1.35 GiB)       | N/A    | 27.40s   | 6.10s    | 1.52s
+
+mold is so fast that it is only 2x _slower_ than the `cp` command on the same
+machine. If you find that mold is not faster than other linkers, feel
+free to [file a bug report](https://github.com/rui314/mold/issues).
+
+mold supports x86-64, i386, ARM64, ARM32, 64-bit/32-bit little/big-endian
+RISC-V, 32-bit PowerPC, 64-bit big-endian PowerPC ELFv1, 64-bit little-endian
+PowerPC ELFv2, s390x, 64-bit/32-bit LoongArch, SPARC64, m68k, and SH-4.
 
 ## Why does linking speed matter?
 
@@ -29,134 +38,50 @@ speed up this process, saving you time and preventing distractions while
 waiting for a lengthy build to finish. The difference is most noticeable
 during rapid debug-edit-rebuild cycles.
 
-## Benchmark
-
-Here is a performance comparison of lld, wild, and mold when linking nine
-large programs on two machines:
-
-- AMD Ryzen Threadripper 7980X (64 cores) running Ubuntu 24.04
-- Apple M1 Ultra (16 performance cores and 4 efficiency cores) running Fedora
-  Asahi Remix 42; the benchmark is restricted to the performance cores
-
-The Threadripper represents many-core workstation and server processors, and
-the M1 Ultra represents high-performance desktop processors.
-
-All three linkers were built from source in release configuration as of
-2026-08-28 and ran with their default options. Times are wall-clock times as
-seen by the caller, the median of three runs after a warm-up. The ARM64 rows
-are the ARM64 builds of the same programs. The benchmark suite, including all
-linker inputs, is available on [Zenodo](https://zenodo.org/records/21882261).
-
-**AMD Ryzen Threadripper 7980X, debug builds**
-
-| Program (output size)             | lld    | wild  | mold  | wild/mold | lld/mold
-|-----------------------------------|--------|-------|-------|-----------|---------
-| Blender 5.2 (2.46 GiB)            | 4.72s  | 1.98s | 0.86s | 2.3x      | 5.5x
-| Chromium 145 (4.51 GiB)           | 16.64s | 3.98s | 1.65s | 2.4x      | 10.1x
-| Chromium 145 ARM64 (4.76 GiB)     | 20.91s | N/A   | 1.83s | N/A       | 11.4x
-| Clang 21 (4.19 GiB)               | 6.19s  | 3.71s | 1.34s | 2.8x      | 4.6x
-| ClickHouse 26.1 (5.58 GiB)        | 6.62s  | 4.40s | 0.98s | 4.5x      | 6.7x
-| Firefox 149 (2.37 GiB)            | 5.11s  | N/A   | 0.78s | N/A       | 6.5x
-| Firefox 149 ARM64 (2.43 GiB)      | 6.40s  | N/A   | 0.93s | N/A       | 6.9x
-| Godot 4.6 (1.01 GiB)              | 1.77s  | 1.08s | 0.46s | 2.3x      | 3.8x
-| LibreOffice 26.2 (0.98 GiB)       | 3.46s  | 1.41s | 0.44s | 3.2x      | 7.9x
-| PyTorch 2.9 (3.51 GiB)            | 4.35s  | 2.48s | 0.80s | 3.1x      | 5.4x
-| TensorFlow 2.21 (9.55 GiB)        | 50.73s | N/A   | 3.15s | N/A       | 16.1x
-
-**AMD Ryzen Threadripper 7980X, release builds**
-
-| Program (output size)             | lld   | wild  | mold  | wild/mold | lld/mold
-|-----------------------------------|-------|-------|-------|-----------|---------
-| Blender 5.2 (0.24 GiB)            | 0.85s | 0.30s | 0.20s | 1.5x      | 4.2x
-| Chromium 145 (0.58 GiB)           | 6.48s | N/A   | 0.64s | N/A       | 10.2x
-| Chromium 145 ARM64 (0.60 GiB)     | 7.91s | N/A   | 0.73s | N/A       | 10.8x
-| Clang 21 (0.21 GiB)               | 0.53s | 0.23s | 0.11s | 2.2x      | 5.0x
-| ClickHouse 26.1 (1.23 GiB)        | 3.18s | 2.07s | 0.41s | 5.0x      | 7.7x
-| Firefox 149 (0.22 GiB)            | 1.01s | 0.41s | 0.21s | 2.0x      | 4.9x
-| Godot 4.6 (0.15 GiB)              | 0.44s | 0.21s | 0.08s | 2.7x      | 5.8x
-| LibreOffice 26.2 (0.19 GiB)       | 1.13s | 0.57s | 0.19s | 3.0x      | 6.0x
-| PyTorch 2.9 (0.31 GiB)            | 0.68s | 0.32s | 0.15s | 2.2x      | 4.7x
-| TensorFlow 2.21 (0.73 GiB)        | 9.62s | N/A   | 0.70s | N/A       | 13.7x
-
-**Apple M1 Ultra, debug builds**
-
-| Program (output size)             | lld    | wild  | mold  | wild/mold | lld/mold
-|-----------------------------------|--------|-------|-------|-----------|---------
-| Blender 5.2 (2.46 GiB)            | 3.21s  | 1.81s | 1.56s | 1.2x      | 2.1x
-| Chromium 145 (4.51 GiB)           | 9.54s  | 3.49s | 2.22s | 1.6x      | 4.3x
-| Chromium 145 ARM64 (4.76 GiB)     | 12.67s | N/A   | 2.31s | N/A       | 5.5x
-| Clang 21 (4.19 GiB)               | 4.40s  | 2.78s | 2.96s | 0.9x      | 1.5x
-| ClickHouse 26.1 (5.58 GiB)        | 4.92s  | 3.50s | 1.71s | 2.1x      | 2.9x
-| Firefox 149 (2.37 GiB)            | 3.21s  | N/A   | 1.12s | N/A       | 2.9x
-| Firefox 149 ARM64 (2.43 GiB)      | 4.13s  | N/A   | 1.12s | N/A       | 3.7x
-| Godot 4.6 (1.01 GiB)              | 1.12s  | 0.81s | 0.62s | 1.3x      | 1.8x
-| LibreOffice 26.2 (0.98 GiB)       | 2.08s  | 0.94s | 0.63s | 1.5x      | 3.3x
-| PyTorch 2.9 (3.51 GiB)            | 3.07s  | 2.10s | 1.45s | 1.4x      | 2.1x
-| TensorFlow 2.21 (9.55 GiB)        | 43.68s | N/A   | 4.43s | N/A       | 9.9x
-
-**Apple M1 Ultra, release builds**
-
-| Program (output size)             | lld   | wild  | mold  | wild/mold | lld/mold
-|-----------------------------------|-------|-------|-------|-----------|---------
-| Blender 5.2 (0.24 GiB)            | 0.56s | 0.20s | 0.25s | 0.8x      | 2.3x
-| Chromium 145 (0.58 GiB)           | 4.25s | N/A   | 0.78s | N/A       | 5.5x
-| Chromium 145 ARM64 (0.60 GiB)     | 5.17s | N/A   | 0.91s | N/A       | 5.7x
-| Clang 21 (0.21 GiB)               | 0.30s | 0.15s | 0.14s | 1.0x      | 2.1x
-| ClickHouse 26.1 (1.23 GiB)        | 1.94s | 0.95s | 0.55s | 1.7x      | 3.5x
-| Firefox 149 (0.22 GiB)            | 0.56s | 0.23s | 0.20s | 1.1x      | 2.7x
-| Godot 4.6 (0.15 GiB)              | 0.26s | 0.11s | 0.11s | 1.0x      | 2.3x
-| LibreOffice 26.2 (0.19 GiB)       | 0.62s | 0.30s | 0.23s | 1.3x      | 2.7x
-| PyTorch 2.9 (0.31 GiB)            | 0.43s | 0.22s | 0.17s | 1.3x      | 2.5x
-| TensorFlow 2.21 (0.73 GiB)        | 8.07s | N/A   | 0.68s | N/A       | 11.9x
-
-N/A indicates that the linker cannot link that program. wild's Chromium
-release links are also marked N/A because wild does not implement `--icf=all`
-and links without identical code folding.
-
-## Why is mold so fast?
-
-mold owes its speed to pervasive parallelism and to efficient data structures
-and algorithms. For details, read our paper "mold: A Massively Parallel
-Linker" (ASPLOS 2027), available at https://arxiv.org/abs/2608.23228.
-
 ## Installation
 
 Binary packages for the following systems are currently available:
 
 [![Packaging status](https://repology.org/badge/vertical-allrepos/mold.svg)](https://repology.org/project/mold/versions)
 
-Prebuilt binaries for Linux on x86-64, ARM64, ARM32, RISC-V, PPC64LE, s390x,
-and LoongArch are also attached to each
-[GitHub release](https://github.com/rui314/mold/releases).
-
 ## How to Build
 
-mold is written in Rust and built with Cargo. It requires Rust 1.95 or later;
-if your system's Rust is older, install the stable toolchain with
-[rustup](https://rustup.rs/). You also need Git and a C compiler such as GCC or
-Clang, which you can install with your system's package manager.
+mold is written in C++20, so if you build mold yourself, you will need a
+recent version of a C++ compiler and a C++ standard library. We recommend GCC
+10.2 or Clang 12.0.0 (or later) and libstdc++ 10 or libc++ 7 (or later).
+
+### Install Dependencies
+
+To install build dependencies, run `./install-build-deps.sh` in this
+directory. It will detect your Linux distribution and attempt to install the
+necessary packages. You may need to run it as root.
 
 ### Compile mold
 
 ```shell
-git clone https://github.com/rui314/mold.git
+git clone --branch stable https://github.com/rui314/mold.git
 cd mold
-cargo build --release
+./install-build-deps.sh
+cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_COMPILER=c++ -B build
+cmake --build build -j$(nproc)
+sudo cmake --build build --target install
 ```
 
-The executable and its companion preload library are
-`target/release/mold` and `target/release/mold-wrapper.so`.
+You might need to pass a C++20 compiler command name to `cmake`. In the
+example above, `c++` is passed. If that doesn't work for you, try a specific
+version of a compiler, such as `g++-10` or `clang++-12`.
 
-### Install mold
+By default, `mold` is installed to `/usr/local/bin`. You can change the
+installation location by passing `-DCMAKE_INSTALL_PREFIX=<directory>`.
+For other cmake options, see the comments in `CMakeLists.txt`.
 
-Run `sudo ./install-mold.sh` to install mold under `/usr/local`. To install it
-under a different prefix, set `PREFIX`, as in
-`sudo PREFIX=/usr ./install-mold.sh`. `mold-wrapper.so` is installed to
-`$PREFIX/lib/mold`. If your system uses another library directory, such as
-`/usr/lib64`, set `MOLD_LIBDIR` to it for both `cargo build` and
-`install-mold.sh`.
-
-You can also run `target/release/mold` directly without installing it.
+If you are not using a recent enough Linux distribution, or if `cmake` does
+not work for you for any reason, you can use Podman to build mold in a
+container. To do so, run `./dist.sh` in this directory instead of using
+`cmake`. The shell script will pull a container image, build mold and auxiliary
+files inside it, and package them into a single tar file named
+`dist/mold-$version-$arch-linux.tar.gz`. You can extract the tar file anywhere
+and use the mold executable in it.
 
 ## How to use
 
@@ -178,10 +103,11 @@ to use mold instead of `/usr/bin/ld`:
   valid argument, so you need to use the `-B` option instead. The `-B` option
   tells GCC where to look for external commands like `ld`.
 
-  If you installed mold using the script above, there is a directory named
-  `/usr/local/libexec/mold`, and the `ld` command there is a symlink to mold.
-  Pass `-B/usr/local/libexec/mold` to GCC. If you installed under another
-  prefix, use that prefix instead.
+  If you have installed mold with `make install`, there should be a directory
+  named `/usr/libexec/mold` (or `/usr/local/libexec/mold`, depending on your
+  `$PREFIX`), and the `ld` command should be there. The `ld` is actually a
+  symlink to `mold`. So, all you need is to pass `-B/usr/libexec/mold` (or
+  `-B/usr/local/libexec/mold`) to GCC.
 
 If you haven't installed `ld.mold` to any `$PATH`, you can still pass
 `-fuse-ld=/absolute/path/to/mold` to clang to use mold. However, GCC does not
@@ -194,7 +120,7 @@ accept an absolute path as an argument for `-fuse-ld`.
 Create `.cargo/config.toml` in your project directory with the following:
 
 ```toml
-[target.'cfg(target_os = "linux")']
+[target.x86_64-unknown-linux-gnu]
 linker = "clang"
 rustflags = ["-C", "link-arg=-fuse-ld=/path/to/mold"]
 ```
@@ -205,7 +131,7 @@ example above, we use `clang` as a linker driver since it always accepts the
 may be able to remove the `linker = "clang"` line.
 
 ```toml
-[target.'cfg(target_os = "linux")']
+[target.x86_64-unknown-linux-gnu]
 rustflags = ["-C", "link-arg=-fuse-ld=mold"]
 ```
 
@@ -255,7 +181,7 @@ mold -run make <make-options-if-any>
 Internally, mold invokes a given command with the `LD_PRELOAD` environment
 variable set to its companion shared object file. The shared object file
 intercepts all function calls to `exec(3)`-family functions to replace
-`argv[0]` with `mold` if it is `ld`, `ld.bfd`, `ld.gold`, or `ld.lld`.
+`argv[0]` with `mold` if it is `ld`, `ld.bf`, `ld.gold`, or `ld.lld`.
 
 </details>
 
@@ -293,26 +219,39 @@ is available online. You can read the same manual by running `man mold`.
 
 </details>
 
-## Stability
+## Why is mold so fast?
 
-mold has been developed in the open since 2020 and has more than 140
-contributors. Its test suite, which covers every linker feature, runs in CI for
-all supported target CPU architectures, natively or under QEMU, and under ASAN
-and TSAN. Before each release, we try to build all of Gentoo Linux's roughly
-19,000 packages with mold, using GNU ld as a control, to find regressions before
-they reach a release.
+One reason is that it utilizes faster algorithms and more efficient data
+structures compared to other linkers. Another reason is that mold is highly
+parallelized.
+
+Here is a side-by-side comparison of per-core CPU usage for lld (left) and
+mold (right), linking the same program, a Chromium executable.
+
+![CPU usage comparison in htop animation](docs/htop.gif)
+
+As you can see, mold uses all available cores throughout its execution and
+finishes quickly. In contrast, lld fails to utilize available cores most of
+the time. In this demo, the maximum parallelism is artificially capped at 16,
+so that the bars fit in the GIF.
+
+For details, please see the [design notes](docs/design.md).
 
 ## Sponsors
 
-mold is free to use, but keeping it maintained is continuous work: supporting
-new architectures and toolchain features, keeping up with the projects that
-depend on it, and making it faster. That work is funded by sponsors. If mold
-saves you or your company time, please consider becoming a
-[GitHub sponsor](https://github.com/sponsors/rui314).
+It is taken for granted nowadays that compiler toolchains can be easily
+installed and used for free, and people may not think too much about the
+individuals behind these "free tools". mold supports many projects, but it
+is essentially a one-person project. This situation is similar to the one
+depicted in the following xkcd illustration.
 
-We thank everyone who sponsors the project. In particular, we'd like to
-acknowledge the following people and organizations who have sponsored
-$128/month or more:
+[![xkcd 2347](https://imgs.xkcd.com/comics/dependency.png)](https://xkcd.com/2347)
+
+If you think that the "Nebraska guy" should be rewarded, please consider
+becoming our [GitHub sponsor](https://github.com/sponsors/rui314)!
+
+We thank everyone who sponsors our project. In particular, we'd like to acknowledge
+the following people and organizations who have sponsored $128/month or more:
 
 ### Corporate sponsors
 

arc.sh

@@ -0,0 +1,29 @@
+#!/bin/bash -x
+set -e
+apt-get install -y git bzip2 ninja-build pkg-config libglib2.0-dev python3-distutils-extra libpixman-1-dev
+
+cd /
+git clone --depth=1 https://github.com/foss-for-synopsys-dwc-arc-processors/qemu.git
+mkdir /qemu/build
+cd /qemu/build
+../configure --static --extra-cflags=-Wno-error
+ninja
+ln -s /qemu/build/qemu-arc /qemu/build/qemu-arc64 /usr/local/bin
+
+
+apt-get install -y libgmp-dev libmpfr-dev texinfo bison yacc flex
+cd /
+git clone --depth=1 https://github.com/foss-for-synopsys-dwc-arc-processors/binutils-gdb.git
+cd /binutils-gdb
+mkdir build
+cd build
+../configure --target=arc-linux
+make -j$(nproc)
+
+
+apt-get install -y mold
+mkdir /build
+cd /build
+cmake -GNinja -DCMAKE_BUILD_TYPE=Debug -DMOLD_USE_MOLD=1 /mold
+ninja
+TRIPLE=arc-linux-gnu bash -x /mold/test/hello-dynamic.sh

arch/README.md

@@ -1,11 +0,0 @@
-# Architecture crates
-
-Each subdirectory is a small crate that instantiates the generic linker for
-one target architecture. Separate crates let Cargo compile the architectures
-in parallel. Instantiating all targets in one crate leaves a long serial
-compilation step.
-
-The shared linker implementation lives in [`src/`](../src/), with
-target-specific code in [`src/target/`](../src/target/). These crates provide
-entry points that the [`cli/`](../cli/) executable selects for the input
-files' target.

arch/arm32/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-arm32"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for arm32"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/arm32/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::Arm32>(cmdline)
-}

arch/arm32be/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-arm32be"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for arm32be"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/arm32be/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::Arm32Be>(cmdline)
-}

arch/arm64/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-arm64"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for arm64"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/arm64/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::Arm64>(cmdline)
-}

arch/arm64be/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-arm64be"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for arm64be"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/arm64be/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::Arm64Be>(cmdline)
-}

arch/i386/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-i386"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for i386"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/i386/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::I386>(cmdline)
-}

arch/loongarch32/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-loongarch32"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for loongarch32"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/loongarch32/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::LoongArch32>(cmdline)
-}

arch/loongarch64/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-loongarch64"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for loongarch64"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/loongarch64/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::LoongArch64>(cmdline)
-}

arch/m68k/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-m68k"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for m68k"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/m68k/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::M68k>(cmdline)
-}

arch/ppc32/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-ppc32"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for ppc32"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/ppc32/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::Ppc32>(cmdline)
-}

arch/ppc64v1/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-ppc64v1"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for ppc64v1"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/ppc64v1/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::Ppc64V1>(cmdline)
-}

arch/ppc64v2/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-ppc64v2"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for ppc64v2"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/ppc64v2/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::Ppc64V2>(cmdline)
-}

arch/riscv32/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-riscv32"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for riscv32"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/riscv32/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::Riscv32>(cmdline)
-}

arch/riscv32be/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-riscv32be"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for riscv32be"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/riscv32be/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::Riscv32Be>(cmdline)
-}

arch/riscv64/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-riscv64"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for riscv64"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/riscv64/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::Riscv64>(cmdline)
-}

arch/riscv64be/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-riscv64be"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for riscv64be"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/riscv64be/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::Riscv64Be>(cmdline)
-}

arch/s390x/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-s390x"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for s390x"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/s390x/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::S390x>(cmdline)
-}

arch/sh4/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-sh4"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for sh4"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/sh4/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::Sh4>(cmdline)
-}

arch/sh4be/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-sh4be"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for sh4be"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/sh4be/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::Sh4Be>(cmdline)
-}

arch/sparc64/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-sparc64"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for sparc64"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/sparc64/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::Sparc64>(cmdline)
-}

arch/x86_64/Cargo.toml

@@ -1,13 +0,0 @@
-[package]
-name = "mold-target-x86_64"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold linker instantiated for x86_64"
-license.workspace = true
-
-[lib]
-path = "lib.rs"
-
-[dependencies]
-mold.workspace = true

arch/x86_64/lib.rs

@@ -1,3 +0,0 @@
-pub fn link(cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    mold::driver::link::<mold::target::X86_64>(cmdline)
-}

build.rs

@@ -1,115 +0,0 @@
-//! Builds the two small C parts of mold.
-//!
-//! `mold-wrapper.so` is the preload library behind `mold -run`. It
-//! interposes the exec family, including the C-variadic `execl` functions
-//! that stable Rust cannot define, so it is a C file. It is placed next to
-//! the `mold` executable, where `-run` looks for it.
-//!
-//! `lto-message.c` adapts the LTO plugin's printf-like diagnostics
-//! callback, which is C-variadic as well, and is linked into mold.
-
-use std::path::{Path, PathBuf};
-use std::process::Command;
-
-// Embed the current git commit hash into the mold executable. We ask git
-// instead of parsing files under .git because the repository format varies
-// (e.g. packed refs, reftable). When building from a source tarball, there's
-// no .git, and the hash is simply omitted.
-fn git_hash(source_dir: &Path) -> Option<String> {
-    let dot_git = source_dir.join(".git");
-    if !dot_git.exists() {
-        // Source archives use the package version. If Git metadata is added
-        // later, a clean rebuild is needed to embed the new commit hash.
-        return None;
-    }
-    if dot_git.is_file() {
-        println!("cargo:rerun-if-changed={}", dot_git.display());
-    }
-
-    let git_path = |name: &str| -> Option<PathBuf> {
-        let output = Command::new("git")
-            .arg("-C")
-            .arg(source_dir)
-            .args(["rev-parse", "--git-path", name])
-            .output()
-            .ok()?;
-        if !output.status.success() {
-            return None;
-        }
-        let path = PathBuf::from(String::from_utf8(output.stdout).ok()?.trim());
-        Some(if path.is_absolute() { path } else { source_dir.join(path) })
-    };
-
-    let reftable = git_path("reftable/tables.list").filter(|p| p.exists());
-    if let Some(head) = git_path("HEAD").filter(|p| p.exists()) {
-        println!("cargo:rerun-if-changed={}", head.display());
-        if let Ok(contents) = std::fs::read_to_string(&head)
-            && let Some(reference) =
-                contents.strip_prefix("ref: ").map(str::trim).filter(|_| reftable.is_none())
-            && let Some(path) = git_path(reference)
-        {
-            // A packed reference may acquire a loose file later.
-            // Watch its nearest existing directory until that happens.
-            if let Some(path) = path.ancestors().find(|p| p.exists()) {
-                println!("cargo:rerun-if-changed={}", path.display());
-            }
-        }
-    }
-    for path in git_path("packed-refs").into_iter().chain(reftable).filter(|p| p.exists()) {
-        println!("cargo:rerun-if-changed={}", path.display());
-    }
-
-    let output =
-        Command::new("git").arg("-C").arg(source_dir).args(["rev-parse", "HEAD"]).output().ok()?;
-    output.status.success().then(|| String::from_utf8_lossy(&output.stdout).trim().to_string())
-}
-
-fn main() {
-    let source_dir = PathBuf::from(std::env::var("CARGO_MANIFEST_DIR").unwrap());
-    let version = std::env::var("CARGO_PKG_VERSION").unwrap();
-    let version = match git_hash(&source_dir) {
-        Some(hash) => format!("mold {version} ({hash}; compatible with GNU ld)"),
-        None => format!("mold {version} (compatible with GNU ld)"),
-    };
-    println!("cargo:rustc-env=MOLD_VERSION={version}");
-
-    println!("cargo:rerun-if-changed=c/mold-wrapper.c");
-    println!("cargo:rerun-if-changed=c/lto-message.c");
-
-    let target_os = std::env::var("CARGO_CFG_TARGET_OS").unwrap();
-    let target_env = std::env::var("CARGO_CFG_TARGET_ENV").unwrap();
-    if target_os == "windows" && target_env == "msvc" {
-        return;
-    }
-
-    let out_dir = PathBuf::from(std::env::var("OUT_DIR").unwrap());
-    let mut build = cc::Build::new();
-    build.opt_level(2).pic(true);
-    if let Ok(sanitizer) = std::env::var("CARGO_CFG_SANITIZE") {
-        build.flag(format!("-fsanitize={sanitizer}"));
-    }
-    build.file("c/lto-message.c").compile("ltomessage");
-
-    if target_os == "windows" || target_os == "macos" {
-        return;
-    }
-
-    // The build directory is inside the actual profile directory. PROFILE
-    // only describes inheritance and need not be that directory's name.
-    let profile_dir = out_dir
-        .ancestors()
-        .find(|path| path.file_name().is_some_and(|name| name == "build"))
-        .and_then(Path::parent)
-        .expect("OUT_DIR must be inside Cargo's build directory");
-    let wrapper = profile_dir.join("mold-wrapper.so");
-    let mut command = build.get_compiler().to_command();
-    command.args(["-shared", "-o"]);
-    command.arg(&wrapper).arg("c/mold-wrapper.c");
-    if target_os == "android" || target_os == "linux" {
-        command.arg("-ldl");
-    }
-    let status = command.status();
-    if !matches!(status, Ok(s) if s.success()) {
-        println!("cargo:warning=could not build mold-wrapper.so; `mold -run` will not work");
-    }
-}

c/lto-message.c

@@ -1,18 +0,0 @@
-// The linker plugin reports diagnostics through a printf-like callback.
-// C-variadic functions can't be defined in stable Rust, so this adapter
-// formats the message and hands it to Rust.
-
-#include <stdarg.h>
-#include <stdio.h>
-
-void mold_lto_report(int level, const char *msg);
-
-int mold_lto_message(int level, const char *fmt, ...) {
-  char buf[1000];
-  va_list ap;
-  va_start(ap, fmt);
-  vsnprintf(buf, sizeof(buf), fmt, ap);
-  va_end(ap);
-  mold_lto_report(level, buf);
-  return 0;
-}

cli/Cargo.toml

@@ -1,72 +0,0 @@
-[package]
-name = "mold-cli"
-version.workspace = true
-edition.workspace = true
-rust-version.workspace = true
-description = "The mold executable"
-license.workspace = true
-
-[[bin]]
-name = "mold"
-path = "main.rs"
-
-[[test]]
-name = "integration"
-path = "integration.rs"
-harness = false
-
-[dependencies]
-mimalloc = { git = "https://github.com/rui314/mimalloc_rust", rev = "3979460494f1cd1e7f936cb8e10f41e927c9f698" }
-mold.workspace = true
-mold-target-x86_64 = { path = "../arch/x86_64", optional = true }
-mold-target-i386 = { path = "../arch/i386", optional = true }
-mold-target-arm32 = { path = "../arch/arm32", optional = true }
-mold-target-arm32be = { path = "../arch/arm32be", optional = true }
-mold-target-arm64 = { path = "../arch/arm64", optional = true }
-mold-target-arm64be = { path = "../arch/arm64be", optional = true }
-mold-target-riscv64 = { path = "../arch/riscv64", optional = true }
-mold-target-riscv64be = { path = "../arch/riscv64be", optional = true }
-mold-target-riscv32 = { path = "../arch/riscv32", optional = true }
-mold-target-riscv32be = { path = "../arch/riscv32be", optional = true }
-mold-target-ppc64v2 = { path = "../arch/ppc64v2", optional = true }
-mold-target-ppc32 = { path = "../arch/ppc32", optional = true }
-mold-target-ppc64v1 = { path = "../arch/ppc64v1", optional = true }
-mold-target-s390x = { path = "../arch/s390x", optional = true }
-mold-target-sparc64 = { path = "../arch/sparc64", optional = true }
-mold-target-m68k = { path = "../arch/m68k", optional = true }
-mold-target-sh4 = { path = "../arch/sh4", optional = true }
-mold-target-sh4be = { path = "../arch/sh4be", optional = true }
-mold-target-loongarch64 = { path = "../arch/loongarch64", optional = true }
-mold-target-loongarch32 = { path = "../arch/loongarch32", optional = true }
-
-[dev-dependencies]
-mold-tests = { path = "../tests" }
-
-# One feature per target. All are built by default; a build for one
-# target alone (`--no-default-features --features x86_64`) is much faster.
-[features]
-default = [
-    "x86_64", "i386", "arm32", "arm32be", "arm64", "arm64be", "riscv64", "riscv64be", "riscv32", "riscv32be",
-    "ppc64v2", "ppc32", "ppc64v1", "s390x", "sparc64", "m68k", "sh4", "sh4be", "loongarch64", "loongarch32",
-]
-system-allocator = []
-x86_64 = ["dep:mold-target-x86_64"]
-i386 = ["dep:mold-target-i386"]
-arm32 = ["dep:mold-target-arm32"]
-arm32be = ["dep:mold-target-arm32be"]
-arm64 = ["dep:mold-target-arm64"]
-arm64be = ["dep:mold-target-arm64be"]
-riscv64 = ["dep:mold-target-riscv64"]
-riscv64be = ["dep:mold-target-riscv64be"]
-riscv32 = ["dep:mold-target-riscv32"]
-riscv32be = ["dep:mold-target-riscv32be"]
-ppc64v2 = ["dep:mold-target-ppc64v2"]
-ppc32 = ["dep:mold-target-ppc32"]
-ppc64v1 = ["dep:mold-target-ppc64v1"]
-s390x = ["dep:mold-target-s390x"]
-sparc64 = ["dep:mold-target-sparc64"]
-m68k = ["dep:mold-target-m68k"]
-sh4 = ["dep:mold-target-sh4"]
-sh4be = ["dep:mold-target-sh4be"]
-loongarch64 = ["dep:mold-target-loongarch64"]
-loongarch32 = ["dep:mold-target-loongarch32"]

cli/build.rs

@@ -1,15 +0,0 @@
-//! Links libatomic into mold on hosts without 64-bit atomics, such as
-//! 32-bit PowerPC. mimalloc uses 64-bit atomics, which C compilers
-//! implement as calls into libatomic on those hosts.
-
-fn main() {
-    println!("cargo:rerun-if-changed=build.rs");
-
-    let widths = std::env::var("CARGO_CFG_TARGET_HAS_ATOMIC").unwrap_or_default();
-    if !widths.split(',').any(|w| w == "64") {
-        // rustc places libraries named by this crate before its dependencies
-        // on the linker command line, where --as-needed would drop libatomic.
-        // Link arguments come after all libraries.
-        println!("cargo:rustc-link-arg-bins=-latomic");
-    }
-}

cli/integration.rs

@@ -1,8 +0,0 @@
-use std::path::Path;
-use std::process::ExitCode;
-
-fn main() -> ExitCode {
-    let root = Path::new(env!("CARGO_MANIFEST_DIR")).parent().unwrap();
-    let cases = [root.join("tests")];
-    mold_tests::run(&cases, Path::new(env!("CARGO_BIN_EXE_mold")))
-}

cli/main.rs

@@ -1,79 +0,0 @@
-//! The `mold` executable: runs the linker instantiated for the target the
-//! inputs are for. Each target is instantiated in a crate of its own so
-//! that the compiler can build them in parallel, and a feature per target
-//! decides which of them are built in.
-
-// A Rust executable can define only one global allocator, so select mimalloc
-// here rather than in the linker library.
-#[cfg(not(feature = "system-allocator"))]
-#[global_allocator]
-static GLOBAL: mimalloc::MiMalloc = mimalloc::MiMalloc;
-
-type LinkFn = fn(mold::driver::Cmdline) -> mold::driver::LinkResult;
-
-// Each target has its own monomorphized link function. Start with the first
-// enabled target and switch to the matching function if the inputs differ.
-const TARGETS: &[(&str, LinkFn)] = &[
-    #[cfg(feature = "x86_64")]
-    ("x86_64", mold_target_x86_64::link),
-    #[cfg(feature = "i386")]
-    ("i386", mold_target_i386::link),
-    #[cfg(feature = "arm32")]
-    ("arm32", mold_target_arm32::link),
-    #[cfg(feature = "arm32be")]
-    ("arm32be", mold_target_arm32be::link),
-    #[cfg(feature = "arm64")]
-    ("arm64", mold_target_arm64::link),
-    #[cfg(feature = "arm64be")]
-    ("arm64be", mold_target_arm64be::link),
-    #[cfg(feature = "riscv64")]
-    ("riscv64", mold_target_riscv64::link),
-    #[cfg(feature = "riscv64be")]
-    ("riscv64be", mold_target_riscv64be::link),
-    #[cfg(feature = "riscv32")]
-    ("riscv32", mold_target_riscv32::link),
-    #[cfg(feature = "riscv32be")]
-    ("riscv32be", mold_target_riscv32be::link),
-    #[cfg(feature = "ppc64v2")]
-    ("ppc64v2", mold_target_ppc64v2::link),
-    #[cfg(feature = "ppc32")]
-    ("ppc32", mold_target_ppc32::link),
-    #[cfg(feature = "ppc64v1")]
-    ("ppc64v1", mold_target_ppc64v1::link),
-    #[cfg(feature = "s390x")]
-    ("s390x", mold_target_s390x::link),
-    #[cfg(feature = "sparc64")]
-    ("sparc64", mold_target_sparc64::link),
-    #[cfg(feature = "m68k")]
-    ("m68k", mold_target_m68k::link),
-    #[cfg(feature = "sh4")]
-    ("sh4", mold_target_sh4::link),
-    #[cfg(feature = "sh4be")]
-    ("sh4be", mold_target_sh4be::link),
-    #[cfg(feature = "loongarch64")]
-    ("loongarch64", mold_target_loongarch64::link),
-    #[cfg(feature = "loongarch32")]
-    ("loongarch32", mold_target_loongarch32::link),
-];
-
-fn link_for_target(target: &str, cmdline: mold::driver::Cmdline) -> mold::driver::LinkResult {
-    for &(name, link) in TARGETS {
-        if name == target {
-            return link(cmdline);
-        }
-    }
-    eprintln!(
-        "mold: unsupported target: {target}; rebuild mold with the appropriate target support"
-    );
-    std::process::exit(1);
-}
-
-fn main() {
-    let Some(&(initial_target, _)) = TARGETS.first() else {
-        eprintln!("mold: no targets enabled; rebuild mold with the appropriate target support");
-        std::process::exit(1);
-    };
-    let args = std::env::args_os().collect();
-    let status = mold::driver::main(args, initial_target, link_for_target);
-    std::process::exit(status);
-}

dist.sh

@@ -1,51 +1,43 @@
 #!/bin/bash
 #
-# This script creates a mold binary distribution. The output is written to
-# the `dist` directory as `mold-$version-$arch-linux.tar.gz` (e.g.
-# `mold-2.42.0-x86_64-linux.tar.gz`).
+# This script creates a mold binary distribution. The output is written in
+# `dist` directory as `mold-$version-$arch-linux.tar.gz` (e.g.,
+# `mold-1.0.3-x86_64-linux.tar.gz`).
 #
-# This script aims to produce reproducible outputs. The container images,
-# Rust toolchain, Cargo dependencies and file timestamps are pinned so that
-# the same git commit can produce a bit-for-bit identical binary file. This
-# property serves as a strong safeguard against supply chain attacks. With
-# a reproducible build, anyone can independently verify that the binary
-# files published on our GitHub release page were built from the git commit
-# tagged for release by rebuilding the binaries themselves.
+# The mold executable created by this script is statically linked to
+# libstdc++ but dynamically linked to libc, libm, libz, and librt, as
+# these libraries almost always exist on any Linux system. We can't
+# statically link libc because doing so would disable dlopen(), which is
+# necessary to open the LTO linker plugin.
+#
+# This script aims to produce reproducible outputs. That means if you run
+# the script twice on the same git commit, it should produce bit-by-bit
+# identical binary files. This property is crucial as a countermeasure
+# against supply chain attacks. With this, you can verify that the binary
+# files distributed on the GitHub release pages are created from the
+# commit with release tags by rebuilding the binaries yourself.
 #
 # Debian provides snapshot.debian.org to host all historical binary
-# packages. Distro package repositories must be pinned as well as the base
-# image before a build is fully reproducible. The loongarch64 build still
-# uses the live Debian sid repository, so it does not yet have that property.
+# packages. We use it to construct Podman images pinned to a
+# particular timestamp.
 #
-# The mold executable created by this script is dynamically linked to the
-# system C runtime and other standard system libraries. We can't statically
-# link glibc because doing so would disable dlopen(), which is required to
-# load the LTO linker plugin.
+# We aim to use a reasonably old Debian version because we'll dynamically
+# link glibc to mold, and a binary linked against a newer version of glibc
+# won't work on a system with an older version of glibc.
 #
-# We use a reasonably old Debian version for the build environment because
-# a binary dynamically linked against a newer version of glibc won't work
-# on a system with an older version of glibc.
+# We want to build mold with Clang rather than GCC because mold's
+# Identical Code Folding works best with the LLVM address significance
+# table (.llvm_addrsig). Building a release binary with GCC yields a
+# slightly larger binary than Clang's.
 #
-# The Rust toolchain is downloaded from the official Rust distribution
-# site. Its version and SHA-256 hash are recorded below, so the toolchain
-# is another pinned build input.
+# We need a recent version of Clang to build mold. If it's not available
+# via apt-get, we'll build it ourselves.
 #
-# This script can be used to create non-native binaries (e.g., building
-# aarch64 binary on x86-64) because Podman automatically runs everything
-# under QEMU if the container image is not native. To use this script for
-# non-native builds, you may need to install the qemu-user-static package.
+# You may need to install qemu-user-static package to build non-native
+# binaries.
 
 set -e -x
-cd "$(dirname "$0")"
-
-# The executable embeds the hash of the Git commit it is built from, and
-# the commit's timestamp is used as the file timestamp, so this script
-# must run in a Git clone. A worktree doesn't work either because its
-# `.git` file refers to a directory outside the build container.
-if [ ! -d .git ]; then
-  echo "$0: must be run in a Git clone of mold" >&2
-  exit 1
-fi
+cd "$(dirname $0)"
 
 usage() {
   echo "Usage: $0 [ x86_64 | aarch64 | arm | riscv64 | ppc64le | s390x | loongarch64 ]"
@@ -55,144 +47,173 @@ usage() {
 case $# in
 0)
   arch=$(uname -m)
-  if [ "$arch" = arm64 ]; then
+  if [ $arch = arm64 ]; then
     arch=aarch64
-  elif [[ "$arch" = arm* ]]; then
+  elif [[ $arch = arm* ]]; then
     arch=arm
   fi
   ;;
 1)
-  arch=$1
+  arch="$1"
   ;;
 *)
   usage
-  ;;
 esac
 
-rust_version=1.97.1
-
-# Switch to the pinned snapshot.debian.org sources that the Debian images
-# ship commented out; the live mirrors no longer carry every architecture.
-apt_setup="sed -i -e '/^deb/d' -e 's/^# deb /deb /g' /etc/apt/sources.list"
+# Create a Podman image.
+if [ "$GITHUB_REPOSITORY" = '' ]; then
+  image=mold-builder-$arch
+  image_build="podman build --arch $arch -t $image -"
+else
+  # If this script is running on GitHub Actions, we want to cache
+  # the created container image in GitHub's container repostiory.
+  image=ghcr.io/$GITHUB_REPOSITORY/mold-builder-$arch
+  image_build="podman build --arch $arch -t $image --output=type=registry --layers --cache-to $image --cache-from $image -"
+fi
 
 case $arch in
 x86_64)
   # Debian 9 (Stretch) released in June 2017.
+  # We use a Google-provided mirror (gcr.io) of the official Docker hub
+  # (docker.io) because docker.io has a strict rate limit policy.
+  cat <<EOF | $image_build
+FROM mirror.gcr.io/library/debian:stretch@sha256:c5c5200ff1e9c73ffbf188b4a67eb1c91531b644856b4aefe86a58d2f0cb05be
+ENV DEBIAN_FRONTEND=noninteractive TZ=UTC
+RUN sed -i -e '/^deb/d' -e 's/^# deb /deb [trusted=yes] /g' /etc/apt/sources.list && \
+  echo 'Acquire::Retries "10"; Acquire::http::timeout "10"; Acquire::Check-Valid-Until "false";' > /etc/apt/apt.conf.d/80-retries && \
+  apt-get update && \
+  apt-get install -y --no-install-recommends wget file make gcc g++ zlib1g-dev libssl-dev && \
+  rm -rf /var/lib/apt/lists
+
+# Build CMake 3.27
+RUN mkdir /build && \
+  cd /build && \
+  wget -O- --no-check-certificate --progress=dot:mega https://cmake.org/files/v3.27/cmake-3.27.7.tar.gz | tar xzf - --strip-components=1 && \
+  ./bootstrap --parallel=\$(nproc) && \
+  make -j\$(nproc) && \
+  make install && \
+  rm -rf /build
+
+# Build GCC 14
+RUN mkdir /build && \
+  cd /build && \
+  wget -O- --no-check-certificate --progress=dot:mega https://ftpmirror.gnu.org/gcc/gcc-14.2.0/gcc-14.2.0.tar.gz | tar xzf - --strip-components=1 && \
+  mkdir gmp mpc mpfr && \
+  wget -O- --no-check-certificate --progress=dot:mega https://ftpmirror.gnu.org/gmp/gmp-6.3.0.tar.gz | tar xzf - --strip-components=1 -C gmp && \
+  wget -O- --no-check-certificate --progress=dot:mega https://ftpmirror.gnu.org/mpc/mpc-1.3.1.tar.gz | tar xzf - --strip-components=1 -C mpc && \
+  wget -O- --no-check-certificate --progress=dot:mega https://ftpmirror.gnu.org/mpfr/mpfr-4.2.1.tar.gz | tar xzf - --strip-components=1 -C mpfr && \
+  ./configure --prefix=/usr --enable-languages=c,c++ --disable-bootstrap --disable-multilib && \
+  make -j\$(nproc) && \
+  make install && \
+  ln -sf /usr/lib64/libstdc++.so.6 /usr/lib/x86_64-linux-gnu/libstdc++.so.6 && \
+  rm -rf /build
+
+# Build GNU binutils 2.43
+RUN mkdir /build && \
+  cd /build && \
+  wget -O- --no-check-certificate --progress=dot:mega https://ftpmirror.gnu.org/binutils/binutils-2.43.tar.gz | tar xzf - --strip-components=1 && \
+  ./configure --prefix=/usr && \
+  make -j\$(nproc) && \
+  make install && \
+  rm -fr /build
+
+# Build Python 3.12.7
+RUN mkdir /build && \
+  cd /build && \
+  wget -O- --no-check-certificate --progress=dot:mega https://www.python.org/ftp/python/3.12.7/Python-3.12.7.tgz | tar xzf - --strip-components=1 && \
+  ./configure && \
+  make -j\$(nproc) && \
+  make install && \
+  rm -rf /build
+
+# Build LLVM 19
+RUN mkdir /build && \
+  cd /build && \
+  wget -O- --no-check-certificate --progress=dot:mega https://github.com/llvm/llvm-project/archive/refs/tags/llvmorg-19.1.7.tar.gz | tar xzf - --strip-components=1 && \
+  mkdir b && \
+  cd b && \
+  cmake -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS=clang ../llvm && \
+  cmake --build . -j\$(nproc) && \
+  cmake --install . --strip && \
+  rm -rf /build
+EOF
+  ;;
+aarch64 | arm | ppc64le | s390x)
+  # Debian 11 (Bullseye) released in August 2021
   #
-  # We use a Google-provided mirror (mirror.gcr.io) instead of the official
-  # Docker Hub (docker.io) because docker.io has a strict rate limit policy.
-  base_image=mirror.gcr.io/library/debian:stretch@sha256:c5c5200ff1e9c73ffbf188b4a67eb1c91531b644856b4aefe86a58d2f0cb05be
-  rust_target=x86_64-unknown-linux-gnu
-  rust_sha256=b4cdbc7cc6b0ee0a2666b1872769fdb2ad8393b28b63952f6493b4b400e4832b
-  ;;
-aarch64)
-  # Debian 11 (Bullseye) released in August 2021.
-  base_image=mirror.gcr.io/library/debian:bullseye-20240904@sha256:8ccc486c29a3ad02ad5af7f1156e2152dff3ba5634eec9be375269ef123457d8
-  rust_target=aarch64-unknown-linux-gnu
-  rust_sha256=2f2496c70bd336a66a4c8baf2d303ba161f3552f192444c3639ba903c7c1e2c5
-  ;;
-arm)
-  # Debian 11 (Bullseye) released in August 2021.
-  base_image=mirror.gcr.io/library/debian:bullseye-20240904@sha256:8ccc486c29a3ad02ad5af7f1156e2152dff3ba5634eec9be375269ef123457d8
-  rust_target=armv7-unknown-linux-gnueabihf
-  rust_sha256=e89c5e33aaddc6ef56857000c9117875c2997e9a1a500bd7b16277c9874b002f
+  # We don't want to build Clang for these targets with Qemu becuase
+  # that'd take extremely long time. Also I believe old build machines
+  # are usually x86-64.
+  cat <<EOF | $image_build
+FROM mirror.gcr.io/library/debian:bullseye-20240904@sha256:8ccc486c29a3ad02ad5af7f1156e2152dff3ba5634eec9be375269ef123457d8
+ENV DEBIAN_FRONTEND=noninteractive TZ=UTC
+RUN sed -i -e '/^deb/d' -e 's/^# deb /deb [trusted=yes] /g' /etc/apt/sources.list && \
+  echo 'Acquire::Retries "10"; Acquire::http::timeout "10"; Acquire::Check-Valid-Until "false";' > /etc/apt/apt.conf.d/80-retries && \
+  apt-get update && \
+  apt-get install -y --no-install-recommends build-essential gcc-10 g++-10 clang-16 cmake && \
+  ln -sf /usr/bin/clang-16 /usr/bin/clang && \
+  ln -sf /usr/bin/clang++-16 /usr/bin/clang++ && \
+  rm -rf /var/lib/apt/lists
+EOF
   ;;
 riscv64)
-  base_image=mirror.gcr.io/riscv64/debian:unstable-20240926@sha256:25654919c2926f38952cdd14b3300d83d13f2d820715f78c9f4b7a1d9399bf48
-  apt_setup="sed -i -e '/^URIs/d' -e 's/^# http/URIs: http/' /etc/apt/sources.list.d/debian.sources"
-  rust_target=riscv64gc-unknown-linux-gnu
-  rust_sha256=59bec35d8febb2ab918fa41cffbaa5b07146a63bdc33f029ff756d70a3151ece
-  ;;
-ppc64le)
-  # Debian 11 (Bullseye) released in August 2021.
-  base_image=mirror.gcr.io/library/debian:bullseye-20240904@sha256:8ccc486c29a3ad02ad5af7f1156e2152dff3ba5634eec9be375269ef123457d8
-  rust_target=powerpc64le-unknown-linux-gnu
-  rust_sha256=ff524eef5a59d801df09ccad5cdaf9ea1f0a07d75cbed2a7e9f013a9eb76a3c1
-  ;;
-s390x)
-  # Debian 11 (Bullseye) released in August 2021.
-  base_image=mirror.gcr.io/library/debian:bullseye-20240904@sha256:8ccc486c29a3ad02ad5af7f1156e2152dff3ba5634eec9be375269ef123457d8
-  rust_target=s390x-unknown-linux-gnu
-  rust_sha256=808268af9e880d41b8cb32b242e38c9bd3ea7aba6409b02fbffa0fbc5370c538
+  cat <<EOF | $image_build
+FROM mirror.gcr.io/riscv64/debian:unstable-20240926@sha256:25654919c2926f38952cdd14b3300d83d13f2d820715f78c9f4b7a1d9399bf48
+ENV DEBIAN_FRONTEND=noninteractive TZ=UTC
+RUN sed -i -e '/^URIs/d' -e 's/^# http/URIs: http/' /etc/apt/sources.list.d/debian.sources && \
+  echo 'Acquire::Retries "10"; Acquire::http::timeout "10"; Acquire::Check-Valid-Until "false";' > /etc/apt/apt.conf.d/80-retries && \
+  apt-get update && \
+  apt-get install -y --no-install-recommends build-essential gcc-14 g++-14 clang-18 cmake && \
+  ln -sf /usr/bin/clang-18 /usr/bin/clang && \
+  ln -sf /usr/bin/clang++-18 /usr/bin/clang++ && \
+  rm -rf /var/lib/apt/lists
+EOF
   ;;
 loongarch64)
-  base_image=mirror.gcr.io/loongarch64/debian:sid@sha256:0356df4e494bbb86bb469377a00789a5b42bbf67d5ff649a3f9721b745cbef77
-  apt_setup="echo 'deb http://deb.debian.org/debian sid main' > /etc/apt/sources.list"
-  rust_target=loongarch64-unknown-linux-gnu
-  rust_sha256=d5a925962854730ae7641420d8337af93988ea4ff47b503a856ec53776c87841
+  # LoongArch build is not reproducible yet
+  cat <<EOF | $image_build
+FROM mirror.gcr.io/loongarch64/debian:sid
+ENV DEBIAN_FRONTEND=noninteractive TZ=UTC
+RUN apt-get update && \
+  apt-get install -y --no-install-recommends build-essential gcc-14 g++-14 clang-19 cmake && \
+  ln -sf /usr/bin/clang-19 /usr/bin/clang && \
+  ln -sf /usr/bin/clang++-19 /usr/bin/clang++ && \
+  rm -rf /var/lib/apt/lists
+EOF
   ;;
 *)
   usage
   ;;
 esac
 
-# Create a Podman image containing the native C tools and a pinned Rust
-# toolchain. The downloaded archive is checked before it is unpacked.
-image=mold-rust-builder-$arch
-archive=rust-$rust_version-$rust_target.tar.gz
-
-podman build --arch "$arch" -t "$image" - <<EOF
-FROM $base_image
-ENV DEBIAN_FRONTEND=noninteractive TZ=UTC
-RUN $apt_setup && \
-  echo 'Acquire::Retries "10"; Acquire::http::timeout "10"; Acquire::Check-Valid-Until "false";' > /etc/apt/apt.conf.d/80-retries && \
-  apt-get update && \
-  apt-get install -y --no-install-recommends build-essential ca-certificates git wget && \
-  rm -rf /var/lib/apt/lists
-RUN mkdir /tmp/rust && \
-  cd /tmp/rust && \
-  wget --progress=dot:mega https://static.rust-lang.org/dist/$archive && \
-  echo '$rust_sha256 $archive' | sha256sum -c && \
-  tar xf $archive && \
-  ./${archive%.tar.gz}/install.sh --prefix=/usr/local --disable-ldconfig && \
-  cd / && \
-  rm -rf /tmp/rust
-EOF
-
-version=$(sed -n 's/^version = "\(.*\)"/\1/p' Cargo.toml)
+version=$(sed -n 's/^project(mold VERSION \(.*\))/\1/p' CMakeLists.txt)
 dest=mold-$version-$arch-linux
 
+# Source tarballs available on GitHub don't contain .git history.
+# Clone the repo if missing.
+[ -d .git ] || git clone --branch v$version --depth 1 --bare https://github.com/rui314/mold .git
+
 # We use the timestamp of the last Git commit as the file timestamp
 # for build artifacts.
-timestamp=$(git log -1 --format=%ct)
-
-# `uname -m` in an ARM32 container running on an ARM64 host reports it
-# not as ARM32 but as ARM64. Keep the reported machine consistent with
-# the ARM32 userspace for any build tool that inspects it.
-setarch=
-[ "$arch" = arm ] && setarch='setarch linux32'
-
-mkdir -p dist "target/dist-vendor-$arch"
-
-# Cargo verifies registry packages against the checksums in Cargo.lock and
-# checks out Git dependencies at the commit recorded there. Vendor them in a
-# separate networked step so that the actual build can run without a network.
-# Cargo's own cache is a tmpfs because the libgit2 inside a 32-bit cargo can't
-# read a bind-mounted ext4 directory (readdir fails with EOVERFLOW under QEMU).
-podman run --arch "$arch" -it --rm --userns=host --pids-limit=-1 \
-  --pull=never --env CARGO_HOME=/cargo --tmpfs /cargo -v "$(pwd):/mold:ro" \
-  -v "$(pwd)/target/dist-vendor-$arch:/vendor" "$image" $setarch \
-  bash -c 'cd /mold && cargo vendor --locked /vendor/sources > /vendor/config.toml'
+timestamp="$(git log -1 --format=%ci)"
 
 # Build mold in a container.
-#
-# SOURCE_DATE_EPOCH is a standardized environment variable that allows
-# build artifacts to appear as if they were built at a specific time.
-# Fixed source, vendor and target paths keep embedded build paths stable.
-podman run --arch "$arch" -it --rm --userns=host --pids-limit=-1 --network=none \
-  --pull=never --env SOURCE_DATE_EPOCH="$timestamp" --env DEST="$dest" \
-  -v "$(pwd):/mold:ro" -v "$(pwd)/dist:/dist" \
-  -v "$(pwd)/target/dist-vendor-$arch:/vendor:ro" "$image" \
-  $setarch bash -c '
+mkdir -p dist
+
+podman run --arch $arch -it --rm --userns=host --pids-limit=-1 --network=none \
+  -v "$(pwd):/mold:ro" -v "$(pwd)/dist:/dist" $image bash -c "
 set -e
-export CARGO_TARGET_DIR=/build/target
-cd /mold
-cargo build --release --frozen --config /vendor/config.toml --package mold-cli
-stage=/build/$DEST
-DESTDIR=/build PREFIX=/$DEST ./install-mold.sh
-strip --strip-unneeded "$stage/bin/mold" "$stage/lib/mold/mold-wrapper.so"
-find "$stage" -print | xargs touch --no-dereference --date="@$SOURCE_DATE_EPOCH"
+mkdir /build
 cd /build
-find "$DEST" -print | sort | tar -cf - --no-recursion --files-from=- | gzip -9nc > "/dist/$DEST.tar.gz"
-sha256sum "/dist/$DEST.tar.gz"
-'
+cmake -DCMAKE_BUILD_TYPE=Release -DMOLD_MOSTLY_STATIC=1 -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ /mold
+cmake --build . -j\$(nproc)
+cmake --install .
+cmake -DMOLD_USE_MOLD=1 .
+cmake --build . -j\$(nproc)
+ctest --output-on-failure -j\$(nproc)
+cmake --install . --prefix $dest --strip
+find $dest -print | xargs touch --no-dereference --date='$timestamp'
+find $dest -print | sort | tar -cf - --no-recursion --files-from=- | gzip -9nc > /dist/$dest.tar.gz
+cp mold /dist
+sha256sum /dist/$dest.tar.gz
+"

docs/bugs.md

@@ -0,0 +1,150 @@
+This is a note about interesting bugs that I met during the
+development of the mold linker.
+
+## GNU IFUNC
+
+Problem: A statically-linked "hello world" program mysteriously
+crashed in `__libc_start_main` function which is called just after
+`_start`.
+
+Investigation: I opened up gdb and found that the program reads a
+bogus value from some array. It looks like `memcpy` failed to copy
+proper data there.  After some investigation, I noticed that `memcpy`
+did't copy data at all but instead returned the address of
+`__memcpy_avx_unaligned` function, which is a real `memcpy` function
+optimized for machines with the AVX registers.
+
+This odd issue was caused by the GNU IFUNC mechanism.  That is, if a
+function symbol has type `STT_GNU_IFUNC`, the function does not do
+what its name suggests to do but instead returns a pointer to a
+function that does the actual job. In this case, `memcpy` is an IFUNC
+function, and it returns an address of `__memcpy_avx_unaligned` which
+is a real `memcpy` function.
+
+IFUNC function addresses are stored to `.got` section in an ELF
+executable.  The dynamic loader executes all IFUNC functions at
+startup to replace their GOT entries with their return values. This
+mechanism allows programs to choose the best implementation among
+variants of the same function at runtime based on the machine info.
+
+If a program is statically-linked, there's no dynamic loader that
+rewrites the GOT entries. Therefore, if a program is
+statically-linked, a libc's startup routine does that on behalf of the
+dynamic loader. Concretely, a startup routine interprets all dynamic
+relocations between `__rela_iplt_start` and `__rela_iplt_stop`
+symbols.  It is linker's responsibility to emit dynamic relocations
+for IFUNC symbols even if it is linking a statically-linked program
+and mark the beginning and the ending of a `.rela.dyn` section with
+the symbols, so that the startup routine can find the relocations.
+
+The bug was my linker didn't define `__rela_iplt_start` and
+`__rela_iplt_stop` symbols. Since these symbols are weak, they are
+initialized to zero. From the point of the initializer function,
+there's no dynamic relocations between `__rela_iplt_start` and
+`__rela_iplt_stop` symbols. That left GOT entries for IFUNC symbols
+untouched.
+
+The proper fix was to emit dynamic relocations for IFUNC symbols and
+define the linker-synthesized symbols. I did that, and the bug was
+fixed.
+
+## stdio buffering
+
+Problem: A statically-linked "Hello world" program prints out the
+message if executed as `./hello`, but it doesn't output anything if
+executed as `./hello | cat`.
+
+Investigation: I knew that the default buffering mode for stdout is
+line buffering (buffer is flushed on every '\n'), but if it is not
+connected to the terminal (i.e. `isatty(2)` returns 0 on
+`STDOUT_FILENO`), it automatically switches to full buffering (buffer
+is flushed when it becomes full). So, it looks like libc failed to
+flush the stdout on program exit for some reason.
+
+I traced all function calls using gdb and noticed that `__libc_atexit`
+was not called. That function seemed to be responsible for buffer
+flushing. I don't know how exactly I found the root cause, but after
+spending an hour or two, I found that `__start___libc_atexit` and
+`__stop___libc_atexit` have value 0 in my linker's output while they
+mark a section containing the address of `__libc_atexit` in GNU ld's
+output.
+
+So, libc doesn't directly call `__libc_atexit` but instead call all
+function pointers between `__start___libc_atexit` and
+`__stop___libc_atexit` symbols. libc puts `__libc_atexit` address in
+`_libc_atexit` section, expecting that the linker automatically
+creates the start and the end marker symbols for the section.
+
+There's an obscure linker feature: if a section name is valid as a C
+identifier (e.g. `foo` or `_foo_bar` but not `.foo`), the linker
+automatically creates marker symbols by prepending `__start_` and
+`__stop_` to the section name. My linker lacked the feature.
+
+I implemented the feature, and the bug was fixed.
+
+## TLS variable initialization
+
+Problem: A statically-linked "hello world" program crashes after
+reading a thread-local variable.
+
+Investigation: Thread-local variables are very different from other
+types of varaibles because there may be more than one instance of the
+same variable in memory. Each thread has its copy of thread-local
+varaibles. `%fs` segment register points the end of the variable area
+for the current thread, and the variables are accessed as an offset
+from `%fs`.
+
+Thread-local variables may be initialized (e.g. `thread_local int x =
+5;`). The linker gathers all thread-local variables and put them into
+`PT_TLS` segment. At runtime, the contents of the segment is used as
+an "initialization image" for new threads. When a new thread is
+created, the image is memcpy'ed to the new thread's thread-local
+variable area. The initialization image itself is read-only at
+runtime.
+
+It took more than a day to find out that memcpy copies the
+initialization image to a different place than the thread-local
+variables reside. That means, thread-local variables had garbage as
+initial values, and the program crashed when using them.
+
+The problem is that I set a very large value (4096) to the alignment
+of `PT_TLS` segment. All `PT_LOAD` segments are naturally aligned to
+the page boundary, so I use the same value for `PT_TLS`, but that was
+a mistake. When a thread initialization routine sets a value to `%fs`,
+it first aligns the end of the thread-local variable area address to
+`PT_TLS` alignment value. So, if you set a large value to `PT_TLS`
+alignment, `%fs` is set to a wrong place.
+
+I fixed `PT_TLS` alignment, and the bug was gone.
+
+## stdio buffering (another issue)
+
+I noticed that a dynamically-linked "hello world" program didn't
+flush its stdout buffer on exit. The cause of the problem was that the
+executable had more than one DT_NEEDED entry for `libc.so`.
+
+DT_NEEDED entries in `.dynamic` section specify a list of shared
+object file names which need to be linked at runtime. I added one
+DT_NEEDED entry for each library specified with the `-l` option.
+The pitfall is, unlike object files, libraries are allowed to
+appear more than once in a command line, and the linker has to
+de-duplicate them before processing. Adding more than one DT_NEEDED
+entry for the same shared object causes mysterious issues like this.
+
+# Copy relocations and symbol aliases
+
+environ, _environ and __environ point to the same location in libc.so,
+so when we create a copy relocation for one of the symbols, we need to
+do that for all of them. Otherwise, they'll end up pointing to different
+places which causes a very mysterious issue.
+
+# DT_DEBUG and gdb
+
+If you forget to add an entry with type DT_DEBUG to .dynamic, gdb's
+`info sharedlibrary` command doesn't print out a list of shared
+libraries loaded to memory. The value of the entry doesn't matter, so
+it can be just zero. The existence of it is important.
+
+#
+
+__EH_FRAME_BEGIN__ in libgcc/crtstuff.c

docs/chart.svg

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docs/coding-guidelines.md

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+# Coding Guidelines
+
+mold is written in C++20, but as is the case with every C++ project,
+it has local coding rules. In this document, I'll explain some of them
+and try to give justifications for why I chose such rules.
+
+## DOs
+
+- Always use `i64` (which is a type alias for `int64_t` in mold) for
+  integers unless you have a reason not to. For example, even if you know
+  that a loop counter won't exceed 100, you should stop thinking about it
+  and just use `i64`.
+
+  Justification: Local variables are usually on CPU registers, so on
+  64-bit CPUs, there's no performance peanlty on choosing `i64` over
+  `i32`. Even if a compiler has to spill register values to the stack,
+  I don't think there's an observable difference between `i32` and
+  `i64`. Therefore, extra 32 bits are essentially free. On 32-bit CPUs,
+  they are not free, but that's OK because we are writing mold for modern
+  computers. mold will still run on 32-bit computers but a bit slowly.
+
+  By always using `i64`, we can eliminate the need to think about the
+  "right" size for each variable. It also reduces the risk of integer
+  overflow.
+
+  Exceptions: If you have to allocate a very large number (e.g. millions)
+  of the same object, its size matters. In that case, use a smaller type.
+
+## DON'Ts
+
+- Don't use `auto` unless its actual type is obvious in the very narrow
+  context. Currently, we use `auto` only for lambdas.
+
+  Justification: I think `auto` makes code writing easier but code reading
+  harder, because readers have to make a guess as to what is the actual
+  type of `auto`. If you are already familiar with the existing codebase,
+  you may be able to guess it easily, but that's not always the case.
+  I want to keep the mold codebase friendly to first-time readers.
+
+- Don't over-use inheritance. In mold, most classes don't have parents,
+  and even if they do, their class hierarchy is very shallow. Currently
+  its height is just two (i.e. abstract classes and their implementations).
+
+  Justification: Designing class hierarchies is fun as it feels like
+  taxonomy, but I don't think that always help writing code. It looks like
+  simpler class hierarchy makes its code simpler.

docs/design.md

@@ -0,0 +1,491 @@
+[This document was written in 2020, and the contents are outdated.
+Specifically, we no longer believe that object preloading is a good
+idea. That being said, most of the points in this document still hold
+even today. Therefore, I'll keep this document as-is.]
+
+## Design and implementation of mold
+
+For the rest of this documentation, I'll explain the design and the
+implementation of mold. If you are only interested in using mold, you
+don't need to read the below.
+
+### Motivation
+
+Here is why I'm writing a new linker:
+
+- Even though lld has significantly improved the situation, linking is
+  still one of the slowest steps in a build. It is especially
+  annoying when I changed one line of code and had to wait for a few
+  seconds or even more for a linker to complete. It should be
+  instantaneous. There's a need for a faster linker.
+
+- The number of cores on a PC has increased a lot lately, and this
+  trend is expected to continue. However, the existing linkers can't
+  take the advantage of the trend because they don't scale well for more
+  cores. I have a 64-core/128-thread machine, so my goal is to create
+  a linker that uses the CPU nicely. mold should be much faster than
+  other linkers on 4 or 8-core machines too, though.
+
+- It looks to me that the designs of the existing linkers are somewhat
+  too similar, and I believe there are a lot of drastically different
+  designs that haven't been explored yet. Developers generally don't
+  care about linkers as long as they work correctly, and they don't
+  even think about creating a new one. So there may be lots of low
+  hanging fruits there in this area.
+
+### Basic design
+
+- In order to achieve a `cp`-like performance, the most important
+  thing is to fix the layout of an output file as quickly as possible, so
+  that we can start copying actual data from input object files to an
+  output file as soon as possible.
+
+- Copying data from input files to an output file is I/O-bounded, so
+  there should be room for doing computationally-intensive tasks while
+  copying data from one file to another.
+
+- We should allow the linker to preload object files from disk and
+  parse them in memory before a complete set of input object files
+  is ready. To do so, we need
+  to split the linker into two in such a way that the latter half of
+  the process finishes as quickly as possible by speculatively parsing
+  and preprocessing input files in the first half of the process.
+
+- One of the most computationally-intensive stage among linker stages
+  is symbol resolution. To resolve symbols, we basically have to throw
+  all symbol strings into a hash table to match undefined symbols with
+  defined symbols. But this can be done in the preloading stage using
+  [string interning](https://en.wikipedia.org/wiki/String_interning).
+
+- Object files may contain a special section called a mergeable string
+  section. The section contains lots of null-terminated strings, and
+  the linker is expected to gather all mergeable string sections and
+  merge their contents. So, if two object files contain the same
+  string literal, for example, the resulting output will contain a
+  single merged string. This step is computationally intensive, but string
+  merging can be done in the preloading stage using string interning.
+
+- Static archives (.a files) contain object files, but the static
+  archive's string table contains only defined symbols of member
+  object files and lacks other types of symbols. That makes static
+  archives unsuitable for speculative parsing. Therefore, the linker
+  should ignore the symbol table of static archive and directly read
+  static archive members.
+
+- If there's a relocation that uses a GOT of a symbol, then we have to
+  create a GOT entry for that symbol. Otherwise, we shouldn't. That
+  means we need to scan all relocation tables to fix the length and
+  the contents of a .got section. This is computationally intensive,
+  but this step is parallelizable.
+
+### Linker Script
+
+Linker script is an embedded language for the linker. It is mainly
+used to control how input sections are mapped to output sections and
+the layout of the output, but it can also do a lot of tricky stuff.
+Its feature is useful especially for embedded programming, but it's
+also an awfully underdocumented and complex language.
+
+We have to implement a subset of the linker script language anwyay,
+because on Linux, /usr/lib/x86_64-linux-gnu/libc.so is (despite its
+name) not a shared object file but actually an ASCII file containing
+linker script code to load the _actual_ libc.so file. But the feature
+set for this purpose is very limited, and it is okay to implement them
+to mold.
+
+Besides that, we really don't want to implement the linker script
+language. But at the same time, we want to satisfy the user needs that
+are currently satisfied with the linker script language. So, what
+should we do? Here is my observation:
+
+- Linker script allows doing a lot of tricky stuff, such as specifying
+  the exact layout of a file, inserting arbitrary bytes between
+  sections, etc. But most of them can be done with a post-link binary
+  editing tool (such as `objcopy`).
+
+- It looks like there are two things that truly cannot be done by a
+  post-link editing tool: (a) mapping input sections to output
+  sections, and (b) applying relocations.
+
+From the above observation, I believe we need to provide only the
+following features instead of the entire linker script language:
+
+- A method to specify how input sections are mapped to output
+  sections, and
+
+- a method to set addresses to output sections, so that relocations
+  are applied based on desired addresses.
+
+I believe everything else can be done with a post-link binary editing
+tool.
+
+### Details
+
+- As we aim to the 1-second goal for Chromium, every millisecond
+  counts. We can't ignore the latency of process exit. If we mmap a
+  lot of files, \_exit(2) is not instantaneous but takes a few hundred
+  milliseconds because the kernel has to clean up a lot of
+  resources. As a workaround, we should organize the linker command as
+  two processes; the first process forks the second process, and the
+  second process does the actual work. As soon as the second process
+  writes a result file to a filesystem, it notifies the first process,
+  and the first process exits. The second process can take time to
+  exit, because it is not an interactive process.
+
+- At least on Linux, it looks like the filesystem's performance to
+  allocate new blocks to a new file is the limiting factor when
+  creating a new large file and filling its contents using mmap.
+  If you already have a large file in the buffer cache, writing to it is
+  much faster than creating a new fresh file and writing to it.
+  Based on this observation, mold overwrites to an existing
+  executable file if exists. My quick benchmark showed that I could
+  save 300 milliseconds when creating a 2 GiB output file.
+  Linux doesn't allow to open an executable for writing if it is
+  running (you'll get a "text busy" error if you attempt). mold
+  falls back to the usual way if it fails to open an output file.
+
+- The output from the linker should be deterministic for the sake of
+  [build reproducibility](https://en.wikipedia.org/wiki/Reproducible_builds)
+  and ease of debugging. This might add a little bit of overhead to
+  the linker, but that shouldn't be too much.
+
+- A .build-id, a unique ID embedded to an output file, is usually
+  computed by applying a cryptographic hash function (e.g. SHA-1) to
+  an output file. This is a slow step, but we can speed it up by
+  splitting a file into small chunks, computing SHA-1 for each chunk,
+  and then computing SHA-1 of the concatenated SHA-1 hashes
+  (i.e. constructing a [Merkle
+  Tree](https://en.wikipedia.org/wiki/Merkle_tree) of height 2).
+  Modern x86 processors have purpose-built instructions for SHA-1 and
+  can compute SHA-1 pretty quickly at about 2 GiB/s. Using 16
+  cores, a build-id for a 2 GiB executable can be computed in 60 to 70
+  milliseconds.
+
+- BFD, gold, and lld support section garbage collection. That is, a
+  linker runs a mark-sweep garbage collection on an input graph, where
+  sections are vertices and relocations are edges, to discard all
+  sections that are not reachable from the entry point symbol
+  (i.e. `_start`) or a few other root sections. In mold, we are using
+  multiple threads to mark sections concurrently.
+
+- Similarly, BFD, gold an lld support Identical Comdat Folding (ICF)
+  as yet another size optimization. ICF merges two or more read-only
+  sections that happen to have the same contents and relocations.
+  To do that, we have to find isomorphic subgraphs from larger graphs.
+  I implemented a new algorithm for mold, which is 5x faster than lld
+  to do ICF for Chromium (from 5 seconds to 1 second).
+
+- [Intel Threading Building
+  Blocks](https://github.com/oneapi-src/oneTBB) (TBB) is a good
+  library for parallel execution and has several concurrent
+  containers. We are particularly interested in using
+  `parallel_for_each` and `concurrent_hash_map`.
+
+- TBB provides `tbbmalloc` which works better for multi-threaded
+  applications than the glib'c malloc, but it looks like
+  [jemalloc](https://github.com/jemalloc/jemalloc) and
+  [mimalloc](https://github.com/microsoft/mimalloc) are a little bit
+  more scalable than `tbbmalloc`.
+
+### Size of the problem
+
+When linking Chrome, a linker reads 3,430,966,844 bytes of data in
+total. The data contains the following items:
+
+| Data item                | Number
+| ------------------------ | ------
+| Object files             | 30,723
+| Public undefined symbols | 1,428,149
+| Mergeable strings        | 1,579,996
+| Comdat groups            | 9,914,510
+| Regular sections¹        | 10,345,314
+| Public defined symbols   | 10,512,135
+| Symbols                  | 23,953,607
+| Sections                 | 27,543,225
+| Relocations against SHF_ALLOC sections | 39,496,375
+| Relocations              | 62,024,719
+
+¹ Sections that have to be copied from input object files to an
+output file. Sections that contain relocations or symbols are for
+example excluded.
+
+### Internals
+
+In this section, I'll explain the internals of mold linker.
+
+#### A brief history of Unix and the Unix linker
+
+Conceptually, what a linker does is pretty simple. A compiler compiles
+a fragment of a program (a single source file) into a fragment of
+machine code and data (an object file, which typically has the .o
+extension), and a linker stitches them together into a single
+executable or a shared library image.
+
+In reality, modern linkers for Unix-like systems are much more
+complicated than the naive understanding because they have gradually
+gained one feature at a time over the 50 years history of Unix, and
+they are now something like a bag of lots of miscellaneous features in
+which none of the features is more important than the others. It is
+very easy to miss the forest for the trees, since for those who don't
+know the details of the Unix linker, it is not clear which feature is
+essential and which is not.
+
+That being said, one thing is clear that at any point of Unix history,
+a Unix linker has a coherent feature set for the Unix of that age. So,
+let me entangle the history to see how the operating system, runtime,
+and linker have gained features that we see today. That should give
+you an idea of why a particular feature has been added to a linker in the
+first place.
+
+1. Original Unix didn't support shared libraries, and a program was
+   always loaded to a fixed address. An executable was something like
+   a memory dump that was just loaded to a particular address by the
+   kernel. After loading, the kernel started executing the program by
+   setting the instruction pointer to a particular address.
+
+   The most essential feature for any linker is relocation processing.
+   The original Unix linker of course supported that. Let me explain
+   what that is.
+
+   Individual object files are inevitably incomplete as a program,
+   because when a compiler created them, it only see a part of an
+   entire program. For example, if an object file contains a function
+   call that refers to another object file, the `call` instruction in the
+   object cannot be complete, as the compiler has no idea as to what
+   is the called function's address. To deal with this, the compiler
+   emits a placeholder value (typically just zero) instead of a real
+   address and leaves metadata in an object file saying "fix offset X
+   of this file with an address of Y". That metadata is called
+   "relocation". Relocations are typically processed by the linker.
+
+   It is easy for a linker to apply relocations for the original Unix
+   because a program is always loaded to a fixed address. It exactly
+   knows the addresses of all functions and data when linking a
+   program.
+
+   Static library support, which is still an important feature of Unix
+   linker, also dates back to this early period of Unix history.
+   To understand what it is, imagine that you are trying to compile
+   a program for the early Unix. You don't want to waste time to
+   compile libc functions every time you compile your program (the
+   computers of the era were incredibly slow), so you have already
+   placed each libc function into a separate source file and compiled
+   them individually. That means you have object files for each libc
+   function, e.g., printf.o, scanf.o, atoi.o, write.o, etc.
+
+   Given this configuration, all you have to do to link your program
+   against libc functions is to pick up the right set of libc object
+   files and give them to the linker along with the object files of your
+   program. But, keeping the linker command line in sync with the
+   libc functions you are using in your program is bothersome. You can
+   be conservative; you can specify all libc object files to the
+   command line, but that leads to program bloat because the linker
+   unconditionally link all object files given to it no matter whether
+   they are used or not. So, a new feature was added to the linker to
+   fix the problem. That is the static library, which is also called
+   the archive file.
+
+   An archive file is just a bundle of object files, just like zip
+   file but in an uncompressed form. An archive file typically has the
+   .a file extension and named after its contents. For example, the
+   archive file containing all libc objects is named `libc.a`.
+
+   If you pass an archive file along with other object files to the
+   linker, the linker pulls out an object file from the archive _only
+   when_ it is referenced by other object files. In other words,
+   unlike object files directly given to a linker, object files
+   wrapped in an archive are not linked to the output by default.
+   An archive works as a supplement to complete your program.
+
+   Even today, you can still find a libc archive file. Run `ar t
+   /usr/lib/x86_64-linux-gnu/libc.a` on Linux should give you a list
+   of object files in the libc archive.
+
+2. In the '80s, Sun Microsystems, a leading commercial Unix vendor at the
+   time, added shared library support to their Unix variant, SunOS.
+
+(This section is incomplete.)
+
+### Concurrency strategy
+
+In this section, I'll explain the high-level concurrency strategy of
+mold.
+
+In most places, mold adopts data parallelism. That is, we have a huge
+number of pieces of data of the same kind, and we process each of them
+individually using parallel for-loop. For example, after identifying
+the exact set of input object files, we need to scan all relocation
+tables to determine the sizes of .got and .plt sections. We do that
+using a parallel for-loop. The granularity of parallel processing in
+this case is the relocation table.
+
+Data parallelism is very efficient and scalable because there's no
+need for threads to communicate with each other while working on each
+element of data. In addition to that, data parallelism is easy to
+understand, as it is just a for-loop in which multiple iterations may
+be executed in parallel. We don't use high-level communication or
+synchronization mechanisms such as channels, futures, promises,
+latches or something like that in mold.
+
+In some cases, we need to share a little bit of data between threads
+while executing a parallel for-loop. For example, the loop to scan
+relocations turns on "requires GOT" or "requires PLT" flags in a
+symbol. Symbol is a shared resource, and writing to them from multiple
+threads without synchronization is unsafe. To deal with it, we made
+the flag an atomic variable.
+
+The other common pattern you can find in mold which is build on top of
+the parallel for-loop is the map-reduce pattern. That is, we run a
+parallel for-loop on a large data set to produce a small data set and
+process the small data set with a single thread. Let me take a
+build-id computation as an example. Build-id is typically computed by
+applying a cryptographic hash function such as SHA-1 on a linker's
+output file. To compute it, we first consider an output as a sequence
+of 1 MiB blocks and compute a SHA-1 hash for each block in parallel.
+Then, we concatenate the SHA-1 hashes and compute a SHA-1 hash on the
+hashes to get a final build-id.
+
+Finally, we use concurrent hashmap at a few places in mold. Concurrent
+hashmap is a hashmap to which multiple threads can safely insert items
+in parallel. We use it in the symbol resolution stage, for example.
+To resolve symbols, we basically have to throw in all defined symbols
+into a hash table, so that we can find a matching defined symbol for
+an undefined symbol by name. We do the hash table insertion from a
+parallel for-loop which iterates over a list of input files.
+
+Overall, even though mold is highly scalable, it succeeded to avoid
+complexties you often find in complex parallel programs. From high
+level, mold just serially executes the linker's internal passes one by
+one. Each pass is parallelized using parallel for-loops.
+
+### Rejected ideas
+
+In this section, I'll explain the alternative designs I currently do
+not plan to implement and why I turned them down.
+
+- Placing variable-length sections at end of an output file and start
+  copying file contents before fixing the output file layout
+
+  Idea: Fixing the layout of regular sections seems easy, and if we
+  place them at beginning of a file, we can start copying their
+  contents from their input files to an output file. While copying
+  file contents, we can compute the sizes of variable-length sections
+  such as .got or .plt and place them at end of the file.
+
+  Reason for rejection: I did not choose this design because I doubt
+  if it could actually shorten link time and I think I don't need it
+  anyway.
+
+  The linker has to de-duplicate comdat sections (i.e. inline
+  functions that are included in multiple object files), so we
+  cannot compute the layout of regular sections until we resolve all
+  symbols and de-duplicate comdats. That takes a few hundred
+  milliseconds. After that, we can compute the sizes of
+  variable-length sections in less than 100 milliseconds. It's quite
+  fast, so it doesn't seem to make much sense to proceed without
+  fixing the final file layout.
+
+  The other reason to reject this idea is because there's good a
+  chance for this idea to have a negative impact on linker's overall
+  performance. If we copy file contents before fixing the layout, we
+  can't apply relocations to them while copying because symbol
+  addresses are not available yet. If we fix the file layout first, we
+  can apply relocations while copying, which is effectively zero-cost
+  due to a very good data locality. On the other hand, if we apply
+  relocations long after we copy file contents, it's pretty expensive
+  because section contents are very likely to have been evicted from
+  CPU cache.
+
+- Incremental linking
+
+  Idea: Incremental linking is a technique to patch a previous linker's
+  output file so that only functions or data that are updated from the
+  previous build are written to it. It is expected to significantly
+  reduce the amount of data copied from input files to an output file
+  and thus speed up linking. GNU BFD and gold linkers support it.
+
+  Reason for rejection: I turned it down because it (1) is
+  complicated, (2) doesn't seem to speed it up that much and (3) has
+  several practical issues. Let me explain each of them.
+
+  First, incremental linking for real C/C++ programs is not as easy as
+  one might think. Let me take malloc as an example. malloc is usually
+  defined by libc, but you can implement it in your program, and if
+  that's the case, the symbol `malloc` will be resolved to your
+  function instead of the one in libc. If you include a library that
+  defines malloc (such as libjemalloc or libtbbmallc) before libc,
+  their malloc will override libc's malloc.
+
+  Assume that you are using a nonstandard malloc. What if you remove
+  your malloc from your code, or remove `-ljemalloc` from your
+  Makefile? The linker has to include a malloc from libc, which may
+  include more object files to satisfy its dependencies. Such code
+  change can affect the entire program rather than just replacing one
+  function. The same is true for adding malloc to your program. Making
+  a local change doesn't necessarily result in a local change in the
+  binary level.  It can easily have cascading effects.
+
+  Some ELF fancy features make incremental linking even harder to
+  implement. Take the weak symbol as an example. If you define `atoi`
+  as a weak symbol in your program, and if you are not using `atoi`
+  at all in your program, that symbol will be resolved to address
+  0. But if you start using some libc function that indirectly calls
+  `atoi`, then `atoi` will be included in your program, and your weak
+  symbol will be resolved to that function. I don't know how to
+  efficiently fix up a binary for this case.
+
+  This is a hard problem, so existing linkers don't try too hard to
+  solve it. For example, IIRC, gold falls back to full link if any
+  function is removed from a previous build. If you want to not annoy
+  users in the fallback case, you need to make full link fast anyway.
+
+  Second, incremental linking itself has an overhead. It has to detect
+  updated files, patch an existing output file and write additional
+  data to an output file for future incremental linking. GNU gold, for
+  instance, takes almost 30 seconds on my machine to do a null
+  incremental link (i.e. no object files are updated from a previous
+  build) for chrome. It's just too slow.
+
+  Third, there are other practical issues in incremental linking. It's
+  not reproducible, so your binary isn't going to be the same as other
+  binaries even if you are compiling the same source tree using the
+  same compiler toolchain. Or, it is complex and there might be a bug
+  in it. If something doesn't work correctly, "remove --incremental
+  from your Makefile and try again" could be a piece of advice, but
+  that isn't ideal.
+
+  So, all in all, incremental linking is tricky. I wanted to make full
+  link as fast as possible, so that we don't have to think about how
+  to work around the slowness of full link.
+
+- Defining a completely new file format and use it
+
+  Idea: Sometimes, the ELF file format itself seems to be a limiting
+  factor in improving the linker's performance. We might be able to make a
+  far better one if we create a new file format.
+
+  Reason for rejection: I rejected the idea because it apparently has
+  a practical issue (backward compatibility issue) and also doesn't
+  seem to improve the performance of linkers that much. As clearly
+  demonstrated by mold, we can create a fast linker for ELF. I believe
+  ELF isn't that bad, after all. The semantics of the existing Unix
+  linkers, such as the name resolution algorithm or the linker script,
+  have slowed the linkers down, but that's not a problem of the file
+  format itself.
+
+- Watching object files using inotify(2)
+
+  Idea: When mold is running as a daemon for preloading, use
+  inotify(2) to watch file system updates so that it can reload files
+  as soon as they are updated.
+
+  Reason for rejection: Just like the maximum number of files you can
+  simultaneously open, the maximum number of files you can watch using
+  inotify(2) isn't that large. Maybe just a single instance of mold is
+  fine with inotify(2), but it may fail if you run multiple of it.
+
+  The other reason for not doing it is because mold is quite fast
+  without it anyway. Invoking stat(2) on each file for file update
+  check takes less than 100 milliseconds for Chrome, and if most of
+  the input files are not updated, parsing updated files takes almost
+  no time.

docs/execstack.md

@@ -0,0 +1,55 @@
+This page explains the following warning message and how to fix it.
+mold emits this message when it sees an object file that may not be
+compatible with mold.
+
+
+```
+mold: warning: foo.o: this file may cause a segmentation fault because it requires an executable stack. See https://github.com/rui314/mold/tree/main/docs/execstack.md for more info.
+```
+
+# Background
+
+On modern computers, the stack area (to which local variables are
+stored) cannot contain executable code. If the control reaches the
+stack area, the CPU refuses to execute any code there and the program
+is usually terminated due to segmentation fault.
+
+This is a security measure. The stack area used to be executable (old
+CPUs generally execute any code as long as it is in a readable memory
+region), but that provided an easy attack vector to a malicious user.
+They wrote executable code to the stack area using some buffer
+overflow bug and jumped there to run arbitrary code in a remote server
+process.
+
+To prevent this type of attack, the stack area is no longer executable
+since the early 2000s. On Linux, the stack's executable-ness is
+controlled by a bit in an executable, and the loader respects that
+bit. The bit is set by the linker.
+
+GCC had (and still has) a feature that depends on the executable
+stack, so they invented a way to tell the linker to mark the stack
+executable. Specifically, if an object file contains a
+`.note.GNU-stack` section with the `SHF_EXECSTACK` bit, GNU linker
+silently makes the stack of an output file executable.
+
+But the GNU linker's behavior is dangerous. If you accidentally link
+an object file that has that marker section, the entire stack area
+silently becomes executable, disabling the security mechanism.
+
+Therefore, mold simply ignores that marker section. If you are using
+mold, you need to explicitly pass `-z execstack` to the linker to make
+the stack executable.
+
+# What caused this issue?
+
+You are likely to use GCC's [Nested
+Functions](https://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html)
+feature which still depends on the executable stack.
+
+# How to fix it?
+
+If you know what you are doing, pass `-z execstack` to mold. Beware
+that this will significantly weaken your program's security.
+
+If you don't want to pass `-z execstack`, rewrite your code so that
+your code does not depend on the executable stack.

docs/glossary.md

@@ -0,0 +1,158 @@
+The very concept of linking is simple: a compiler compiles a piece of
+source code into an object file (a file containing machine code), and
+a linker combines object files into a single executable or a shared
+library file. However, the actual implementation of the linker for
+modern systems is much more complicated because hardware, operating
+system, compiler and linker all have many more features.
+
+In this file, I'll explain random topics in the glossary format that
+you need to understand to read mold code.
+
+## DSO
+
+A .so file. Short for Dynamic Shared Object. Often called as a
+shared library, a dynamic libray or a shared object as well.
+
+An DSO contains common functions and data that are used by multiple
+executables and/or other DSOs. At runtime, a DSO is loaded to a
+contiguous region in the virtual address.
+
+## Object file
+
+A .o file. An object file contains machine code and data, but it
+cannot be executed because it's not self-contained. For example,
+if you compile a C source file containing a call of `printf`,
+the actual function code of `printf` is not included in the resulting
+object file. You include `stdio.h`, but that teaches the compiler
+only about `printf`'s type, and the compiler still don't know what
+`printf` actually does. Therefore, it cannot emit code for `printf`.
+
+You need to link an object file with other object file or a shared
+library to make it exectuable.
+
+## Virtual address space
+
+A pointer has a value like 0x803020 which is an address of the
+pointee. But it doesn't mean that the pointee resides at the
+physical memory address 0x803020 on the computer. Modern CPUs
+contains so-called Mmeory Management Unit (MMU), and all access to
+the memory are first translated by MMU to the physical address.
+The address before translation is called the "virtual address".
+Unless you are doing the kernel programming, all addresses you
+handle are virtual addresses.
+
+The OS kernel controls the MMU so that each process owns the entire
+virtual address space. So, even if two process uses the same virtual
+address, they don't conflict. They are mapped to different physical
+addresses.
+
+The existence of MMU has several implications to the linker. First,
+we can link the main executable to a specific address. On process
+startup, there's no code or data in the virtual address space, so
+the mapping of the main executable always succeed. However, it's not
+true to DSOs because they are loaded after the main executable and
+possibly other DSOs. Therefore, shared libraries must be linked in a
+way that they can be loaded to any address in the virtual address
+space.
+
+## Relocation
+
+A piece of information for the linker as to how to link object files
+or a dynamic objects.
+
+Object files can refer functions or data in other object files. For
+example, if you compile a function which calls a non-local function
+`foo`, the resulting code contains something like this:
+
+```
+  26:   e8 00 00 00 00          callq  2b <bar+0xb>
+                        27: R_X86_64_PLT32      foo-0x4
+```
+
+The above `callq` is the instruction to call a function at the
+machine code level. It's opcode is `0xe8` in x86-64, so the
+instruction begins with `0xe8`. The following four bytes are
+displacement; that is, the address of the branch target relative to
+the end of this `callq` instruction. Notice that the displacement is
+0. The compiler couldn't fill the displacement because it has no
+idea as to where `foo` will be at runtime. So, the compiler write 0
+as a placeholder and instead write a relocation `R_X86_64_PLT32`
+with `foo` as its associated symbol. The linker reads this
+relocation, computes the offsets between this call instruction and
+function `foo` and overwrite the placeholder value 0 with an actual
+displacement.
+
+There are many different types of relocations. For example, if you
+want to fix up not with a displacement but with an absolute address
+of a symbol, you need to use `R_X86_64_ABS64` instead.
+
+## Static library
+
+A .a file. Often called as an archive file or just archive as well.
+
+A static library is a container just like tar or zip. Actually,
+there's no technical reason to not use tar or (uncompressed) zip,
+but traditionally the .a file format is used by the linker.
+
+A static library contains object files and can be passed to the
+linker along with other object files and/or archives.
+
+A linker pulls out object files from an archive only if it is needed
+to resolve undefined symbols. In other words, object files in an
+archive are not linked by default and used as a complement to supply
+missing definitions. This is ideal for a library because you don't
+want to link library functions unless you are actually using them.
+
+Contrary to archive files, object files directly given to a linker
+are always linked to the output.
+
+To maximize the benefit of archive files, a library often used as a
+static library is broken down to small files to separate each
+function individually (for example, look at
+https://git.musl-libc.org/cgit/musl/tree/src/stdio). By doing this,
+you import only used functions.
+
+A static file is created by `ar`, whose command line arguments are
+similar to `tar`. A static library contains the symbol table which
+offers a quick way to look up an object file for a defined symbol,
+but mold does not use the static library's symbol table. mold
+doesdn't need a symbol table to exist in an archive, and if exists,
+mold just ignores it.
+
+See also: DSO (dynamic library)
+
+## Symbol
+
+A symbol is a label assigned to a specific location in an input file
+or an output file. For example, if you define function `foo` and
+compile it, the resulting object file contains a symbol `foo`
+pointing to the beginning of the machine code for `foo`.
+
+Usually, a symbol name is a function or a variable name. If an
+object is anonymous (such the one for a string literal), a compiler
+generated a unique symbol, which often starts with `.` to avoid
+conflict with user-defined symbols.
+
+For C++, symbol name is a complex "mangled" name. We need to mangle
+identifiers because a simple name such as `foo` cannot be uniquely
+identify a function or a data in C++, because for example `foo` may
+be in a namespace or defined as a static member in some class. If
+`foo` is an overloaded function, we need to distinguish different
+`foo`s by its type. Therefore, C++ compiler mangles an identifier by
+appending nmaepsace names, type information and such so that
+different things get different names.
+
+For example, a function `int foo(int)` in a namespace `bar` is
+mangled as `_ZN3bar3fooEi`.
+
+A symbol can be either defined or undefined. A defined symbol points
+to some location in a file which may contain the function's machine
+code or the variable's initial value. An undefined symbol does not
+point to anywhere. It needs to be merged with a defined symbol with
+the same name at link-time. This merging process is called "name
+resolution".
+
+For example, if your program is using `printf`, it usually contains
+`printf` as an undefined symbol. You need to link it with `libc.a`
+or `libc.so`, which contain a defined symbol of `printf`, to make a
+complete program.

docs/mold.1

@@ -1,6 +1,6 @@
 .\" generated with Ronn-NG/v0.9.1
 .\" http://github.com/apjanke/ronn-ng/tree/0.9.1
-.TH "MOLD" "1" "October 2026" ""
+.TH "MOLD" "1" "February 2025" ""
 .SH "NAME"
 \fBmold\fR \- a modern linker
 .SH "SYNOPSIS"
@@ -48,11 +48,9 @@ Whether good or bad, you should keep these semantics in mind to understand Unix
 .P
 \fBmold\fR does not have any host\-specific default settings\. This is contrary to the GNU linkers, for which some configurable values, such as system\-dependent library search paths, are hard\-coded\. \fBmold\fR depends only on its command\-line arguments\.
 .SH "OPTION NOTATIONS"
-Long options are spelled with two dashes\. Some also accept a single dash, but which ones do is somewhat arbitrary for historical reasons\. \fBmold\fR follows the conventions of other linkers for compatibility\. For example, \fB\-\-export\-dynamic\fR can be spelled \fB\-export\-dynamic\fR, while \fB\-\-execute\-only\fR requires two dashes\.
+Multi\-letter long options may precede either a single dash or double dashes, except for those starting with the letter "o"\. For historical reasons, long options beginning with "o" must precede double dashes\.
 .P
-This can cause unexpected behavior when constructing command\-line options in a script\. For example, you might use \fB"\-e$foo"\fR to set the entry point symbol to the value of \fB$foo\fR\. However, if \fB$foo\fR is \fBxport\-dynamic\fR, the argument becomes \fB\-export\-dynamic\fR and is interpreted as \fB\-\-export\-dynamic\fR\.
-.P
-To avoid such ambiguities, we recommend always using two dashes for long options and separating a single\-letter option from its argument with a space\. For example, use \fB\-e $foo\fR or \fB\-\-entry=$foo\fR to specify the entry point symbol in a script\.
+For example, you can spell \fB\-\-as\-needed\fR as \fB\-as\-needed\fR, but \fB\-\-omagic\fR must not be spelled as \fB\-omagic\fR\. \fB\-omagic\fR will be interpreted not as \fB\-\-omagic\fR but as \fB\-o magic\fR\.
 .SH "MOLD\-SPECIFIC OPTIONS"
 .TP
 \fB\-\-chroot\fR=\fIdir\fR
@@ -72,8 +70,6 @@ Permit or do not permit mold to create a debug info file in the background\.
 .TP
 \fB\-\-fork\fR, \fB\-\-no\-fork\fR
 Spawn a child process and let it do the actual linking\. When linking a large program, the OS kernel can take a few hundred milliseconds to terminate a \fBmold\fR process\. \fB\-\-fork\fR hides that latency\. By default, it does fork\.
-.IP
-Note that \fB\-\-fork\fR also hides the resource usage statistics reported by time(2), since it doesn't call waitpid(2) on the child process\. If you need those statistics, pass \fB\-\-no\-fork\fR\.
 .TP
 \fB\-\-perf\fR
 Print performance statistics\.
@@ -134,17 +130,6 @@ Use multiple threads\. By default, \fBmold\fR uses as many threads as the number
 \fB\-\-quick\-exit\fR, \fB\-\-no\-quick\-exit\fR
 Use or do not use \fBquick_exit\fR to exit\.
 .TP
-\fB\-\-zero\-to\-bss\fR
-Convert all\-zero data sections into BSS\.
-.IP
-When this option is enabled, \fBmold\fR scans input data sections that are not of type \fBSHT_NOBITS\fR and checks whether their contents consist solely of zero bytes\. Such sections are then converted into BSS (\fBSHT_NOBITS\fR) sections\. This reduces the size of the output file, since BSS sections occupy no space in the file image\.
-.IP
-This behavior is especially useful for user\-defined sections created with \fB__attribute__((section("\.sectname")))\fR that contain uninitialized global variables\. GCC and Clang do not automatically mark such sections as BSS even if their contents are entirely zero, and instead emit them as regular data sections\.
-.IP
-For example, consider \fB__attribute__((section("\.sectname"))) int vec[256];\fR\.
-.IP
-By default, this results in a \fB\.sectname\fR section of type \fBSHT_PROGBITS\fR filled with zeros\. With \fB\-\-zero\-to\-bss\fR, the linker will recognize it as empty data and convert it to a \fBSHT_NOBITS\fR section, reducing the output file size without changing runtime semantics\.
-.TP
 \fB\-z rewrite\-endbr\fR, \fB\-z norewrite\-endbr\fR
 As a security measure, some CPU instruction sets have recently gained a feature to protect control flow integrity by disallowing indirect branches by default\. If the feature is enabled, the instruction that is executed immediately after an indirect branch must be an branch target marker instruction, or a CPU\-level fault will raise\. The marker instruction is also known as "landing pad" instruction, to which indirect branches can land\. This feature makes ROP attacks harder to conduct\.
 .IP
@@ -154,9 +139,7 @@ By default, the compiler always emits a landing pad at the beginning of each glo
 .IP
 If \fB\-\-rewrite\-endbr\fR is given, mold conducts a whole program analysis to identify functions whose addresses are actually taken and rewrites landing pads with no\-ops for non\-address\-taken functions, reducing the attack surface\.
 .IP
-This feature is currently available only on x86\-64 and arm64\.
-.IP
-On arm64, the landing pad is \fBbti c\fR\. Note that code compiled with \fB\-mbranch\-protection=standard\fR (BTI + pointer authentication) starts functions with \fBpaciasp\fR, which doubles as a landing pad, so there is no separate \fBbti c\fR to rewrite and this option has no effect on such code\.
+This feature is currently available only on x86\-64\.
 .SH "GNU\-COMPATIBLE OPTIONS"
 .TP
 \fB\-\-help\fR
@@ -197,10 +180,7 @@ Omit \fB\.debug_*\fR sections from the output file\.
 Read linker script from \fIfile\fR\.
 .TP
 \fB\-X\fR, \fB\-\-discard\-locals\fR
-Discard temporary local symbols to reduce the sizes of the symbol table and the string table\. Temporary local symbols are local symbols starting with \fB\.L\fR\. Compilers usually generate such symbols for unnamed program elements such as string literals or floating\-point literals\. This is the default; use \fB\-\-discard\-none\fR to keep temporary local symbols\.
-.TP
-\fB\-\-discard\-none\fR
-Keep all local symbols in the symbol table, including temporary ones starting with \fB\.L\fR, except ones in mergeable sections\. This restores the default behavior of GNU ld\. \fBmold\fR and \fBld\.lld\fR discard temporary local symbols by default\.
+Discard temporary local symbols to reduce the sizes of the symbol table and the string table\. Temporary local symbols are local symbols starting with \fB\.L\fR\. Compilers usually generate such symbols for unnamed program elements such as string literals or floating\-point literals\.
 .TP
 \fB\-e\fR \fIsymbol\fR, \fB\-\-entry\fR=\fIsymbol\fR:
 
@@ -265,9 +245,6 @@ Alias for \fB\-\-section\-start=\.data=\fR\fIaddress\fR\.
 \fB\-\-Ttext\fR=\fIaddress\fR
 Alias for \fB\-\-section\-start=\.text=\fR\fIaddress\fR\.
 .TP
-\fB\-\-Ttext\-segment\fR=\fIaddress\fR
-Set the address of the first byte of the text segment\.
-.TP
 \fB\-\-allow\-multiple\-definition\fR
 Normally, the linker reports an error if there are more than one definition of a symbol\. This option changes the default behavior so that it doesn't report an error for duplicate definitions and instead use the first definition\.
 .TP
@@ -292,8 +269,8 @@ Synonym for \fB\-\-build\-id=sha256\fR\.
 \fB\-\-no\-build\-id\fR
 Synonym for \fB\-\-build\-id=none\fR\.
 .TP
-\fB\-\-compress\-debug\-sections\fR=[ \fBzlib\fR | \fBzlib\-gabi\fR | \fBzlib:\fR\fIN\fR | \fBzstd\fR | \fBzstd:\fR\fIN\fR | \fBnone\fR ]
-Compress DWARF debug info (\fB\.debug_*\fR sections) using the zlib or zstd compression algorithm\. \fBzlib\-gabi\fR is an alias for \fBzlib\fR\. \fBzlib:\fR\fIN\fR selects the zlib compression level, where \fIN\fR is between 0 and 9 (0 means no compression), and \fBzstd:\fR\fIN\fR selects the zstd compression level, where \fIN\fR is between 1 and 22\. Higher levels achieve better compression ratios but are slower\. \fBzlib\fR is equivalent to \fBzlib:1\fR and \fBzstd\fR is equivalent to \fBzstd:3\fR\.
+\fB\-\-compress\-debug\-sections\fR=[ \fBzlib\fR | \fBzlib\-gabi\fR | \fBzstd\fR | \fBnone\fR ]
+Compress DWARF debug info (\fB\.debug_*\fR sections) using the zlib or zstd compression algorithm\. \fBzlib\-gabi\fR is an alias for \fBzlib\fR\.
 .TP
 \fB\-\-defsym\fR=\fIsymbol\fR=\fIvalue\fR
 Define \fIsymbol\fR as an alias for \fIvalue\fR\.
@@ -381,16 +358,10 @@ Embed a specified string into the \fB\.note\.package\fR section\. This option is
 .IP
 An argument to this option is treated as percent\-encoded and decoded before being inserted into the section, allowing you to avoid the use of the comma (\fB,\fR) character in the argument\. This is useful because the compiler replaces all occurrences of commas in \fB\-Wl,\fR with spaces before forwarding them to the linker\. Note that \fBmold\fR always interprets the argument as percent\-encoded, so you also need to escape all occurrences of \fB%\fR as \fB%25\fR\.
 .TP
-\fB\-\-pack\-dyn\-relocs\fR=[ \fBrelr\fR | \fBandroid\fR | \fBandroid+relr\fR | \fBnone\fR ]
-Compress dynamic relocations in the output file\.
-.IP
+\fB\-\-pack\-dyn\-relocs\fR=[ \fBrelr\fR | \fBnone\fR ]
 If \fBrelr\fR is specified, all \fBR_*_RELATIVE\fR relocations are put into \fB\.relr\.dyn\fR section instead of \fB\.rel\.dyn\fR or \fB\.rela\.dyn\fR section\. Since \fB\.relr\.dyn\fR section uses a space\-efficient encoding scheme, specifying this flag can reduce the size of the output\. This is typically most effective for position\-independent executable\.
 .IP
-If \fBandroid\fR is specified, all dynamic relocations are encoded in Android's packed relocation format (APS2) and stored in the \fB\.rel\.dyn\fR or \fB\.rela\.dyn\fR section, whose section type is changed to \fBSHT_ANDROID_REL\fR or \fBSHT_ANDROID_RELA\fR\. The dynamic table is updated to use \fBDT_ANDROID_REL\fR / \fBDT_ANDROID_RELA\fR and their \fBSZ\fR variants in place of the standard tags\.
-.IP
-\fBandroid+relr\fR combines both: \fBR_*_RELATIVE\fR relocations go to \fB\.relr\.dyn\fR and the rest are APS2\-encoded\. This is the configuration used by most Android system binaries\.
-.IP
-Note that a runtime loader has to support \fB\.relr\.dyn\fR to run executables or shared libraries linked with \fB\-\-pack\-dyn\-relocs=relr\fR\. As of 2026, glibc (since 2\.36), musl (since 1\.2\.4), Android, ChromeOS, and Fuchsia all support it\. The APS2 format, on the other hand, is only handled by Android's bionic loader; the encoder itself is target\-agnostic, but the produced binary can only be loaded on platforms where bionic (or a compatible loader) handles \fBDT_ANDROID_REL(A)\fR\.
+Note that a runtime loader has to support \fB\.relr\.dyn\fR to run executables or shared libraries linked with \fB\-\-pack\-dyn\-relocs=relr\fR\. As of 2022, only ChromeOS, Android and Fuchsia support it\.
 .TP
 \fB\-\-pie\fR, \fB\-\-pic\-executable\fR, \fB\-\-no\-pie\fR, \fB\-\-no\-pic\-executable\fR
 Create a position\-independent executable\.
@@ -456,9 +427,6 @@ How to handle undefined symbols\.
 \fB\-\-version\-script\fR=\fIfile\fR
 Read version script from \fIfile\fR\. If \fIfile\fR does not exist in the current directory, it is searched from library search paths for the sake of compatibility with GNU ld\.
 .TP
-\fB\-w\fR, \fB\-\-no\-warnings\fR
-Suppress warnings and cancel \fB\-\-fatal\-warnings\fR\.
-.TP
 \fB\-\-warn\-common\fR, \fB\-\-no\-warn\-common\fR
 Warn about common symbols\.
 .TP
@@ -515,22 +483,22 @@ By default, \fBmold\fR generates a relro segment\. \fB\-z norelro\fR disables th
 \fB\-z separate\-loadable\-segments\fR, \fB\-z separate\-code\fR, \fB\-z noseparate\-code\fR
 If one memory page contains multiple segments, the page protection bits are set in such a way that the needed attributes (writable or executable) are satisfied for all segments\. This usually happens at a boundary of two segments with two different attributes\.
 .IP
-\fBseparate\-loadable\-segments\fR adds paddings between segments with different attributes so that they do not share the same page\.
+\fBseparate\-loadable\-segments\fR adds paddings between segments with different attributes so that they do not share the same page\. This is the default\.
 .IP
 \fBseparate\-code\fR adds paddings only between executable and non\-executable segments\.
 .IP
-\fBnoseparate\-code\fR does not add any paddings between segments\. This is the default\.
+\fBnoseparate\-code\fR does not add any paddings between segments\.
 .TP
-\fB\-z defs\fR, \fB\-z undefs\fR
+\fB\-z defs\fR, \fB\-z nodefs\fR
 Report undefined symbols (even with \fB\-\-shared\fR)\.
 .TP
 \fB\-z shstk\fR
 Enforce shadow stack by turning \fBGNU_PROPERTY_X86_FEATURE_1_SHSTK\fR bit in \fB\.note\.gnu\.property\fR output section\. Shadow stack is part of Intel Control\-flow Enforcement Technology (CET), which is available since Tiger Lake (2020)\.
 .TP
-\fB\-z start\-stop\-visibility\fR=[ \fBhidden\fR | \fBprotected\fR ]
+\fB\-z start_stop_visibility\fR=[ \fBhidden\fR | \fBprotected\fR ]
 If a section name is valid as a C identifier (i\.e\., it matches \fB/^[_a\-zA\-Z][_a\-zA\-Z0\-9]*$/\fR), mold creates \fB__start_SECNAME\fR and \fB__stop_SECNAME\fR symbols to mark the beginning and end of the section, where \fBSECNAME\fR is the section name\.
 .IP
-You can make these marker symbols visible from other ELF modules by passing \fB\-z start\-stop\-visibility=protected\fR\. Default is \fBhidden\fR\.
+You can make these marker symbols visible from other ELF modules by passing \fB\-z start_stop_visibility=protected\fR\. Default is \fBhidden\fR\.
 .TP
 \fB\-z text\fR, \fB\-z notext\fR, \fB\-z textoff\fR
 \fBmold\fR by default reports an error if dynamic relocations are created in read\-only sections\. If \fB\-z notext\fR or \fB\-z textoff\fR are given, \fBmold\fR creates such dynamic relocations without reporting an error\. \fB\-z text\fR restores the default behavior\.

docs/mold.md

@@ -127,21 +127,13 @@ arguments.
 
 ## OPTION NOTATIONS
 
-Long options are spelled with two dashes. Some also accept a single dash,
-but which ones do is somewhat arbitrary for historical reasons. `mold`
-follows the conventions of other linkers for compatibility. For example,
-`--export-dynamic` can be spelled `-export-dynamic`, while `--execute-only`
-requires two dashes.
+Multi-letter long options may precede either a single dash or double dashes,
+except for those starting with the letter "o". For historical reasons, long
+options beginning with "o" must precede double dashes.
 
-This can cause unexpected behavior when constructing command-line options in
-a script. For example, you might use `"-e$foo"` to set the entry point symbol
-to the value of `$foo`. However, if `$foo` is `xport-dynamic`, the argument
-becomes `-export-dynamic` and is interpreted as `--export-dynamic`.
-
-To avoid such ambiguities, we recommend always using two dashes for long
-options and separating a single-letter option from its argument with a
-space. For example, use `-e $foo` or `--entry=$foo` to specify the entry
-point symbol in a script.
+For example, you can spell `--as-needed` as `-as-needed`, but `--omagic` must
+not be spelled as `-omagic`. `-omagic` will be interpreted not as `--omagic`
+but as `-o magic`.
 
 ## MOLD-SPECIFIC OPTIONS
 
@@ -167,10 +159,6 @@ point symbol in a script.
   program, the OS kernel can take a few hundred milliseconds to terminate a
   `mold` process. `--fork` hides that latency. By default, it does fork.
 
-  Note that `--fork` also hides the resource usage statistics reported by
-  time(2), since it doesn't call waitpid(2) on the child process. If you
-  need those statistics, pass `--no-fork`.
-
 * `--perf`:
   Print performance statistics.
 
@@ -279,28 +267,6 @@ point symbol in a script.
 * `--quick-exit`, `--no-quick-exit`:
   Use or do not use `quick_exit` to exit.
 
-* `--zero-to-bss`:
-  Convert all-zero data sections into BSS.
-
-  When this option is enabled, `mold` scans input data sections that are not
-  of type `SHT_NOBITS` and checks whether their contents consist solely of
-  zero bytes. Such sections are then converted into BSS (`SHT_NOBITS`)
-  sections. This reduces the size of the output file, since BSS sections
-  occupy no space in the file image.
-
-  This behavior is especially useful for user-defined sections created with
-  `__attribute__((section(".sectname")))` that contain uninitialized global
-  variables. GCC and Clang do not automatically mark such sections as BSS
-  even if their contents are entirely zero, and instead emit them as regular
-  data sections.
-
-  For example, consider `__attribute__((section(".sectname"))) int vec[256];`.
-
-  By default, this results in a `.sectname` section of type `SHT_PROGBITS`
-  filled with zeros. With `--zero-to-bss`, the linker will recognize it as
-  empty data and convert it to a `SHT_NOBITS` section, reducing the output
-  file size without changing runtime semantics.
-
 * `-z rewrite-endbr`, `-z norewrite-endbr`:
   As a security measure, some CPU instruction sets have recently gained a
   feature to protect control flow integrity by disallowing indirect branches
@@ -326,12 +292,7 @@ point symbol in a script.
   landing pads with no-ops for non-address-taken functions, reducing the
   attack surface.
 
-  This feature is currently available only on x86-64 and arm64.
-
-  On arm64, the landing pad is `bti c`. Note that code compiled with
-  `-mbranch-protection=standard` (BTI + pointer authentication) starts
-  functions with `paciasp`, which doubles as a landing pad, so there is no
-  separate `bti c` to rewrite and this option has no effect on such code.
+  This feature is currently available only on x86-64.
 
 ## GNU-COMPATIBLE OPTIONS
 
@@ -388,14 +349,7 @@ point symbol in a script.
   Discard temporary local symbols to reduce the sizes of the symbol table and
   the string table. Temporary local symbols are local symbols starting with
   `.L`. Compilers usually generate such symbols for unnamed program elements
-  such as string literals or floating-point literals. This is the default;
-  use `--discard-none` to keep temporary local symbols.
-
-* `--discard-none`:
-  Keep all local symbols in the symbol table, including temporary ones
-  starting with `.L`, except ones in mergeable sections. This restores the
-  default behavior of GNU ld. `mold` and `ld.lld` discard temporary local
-  symbols by default.
+  such as string literals or floating-point literals.
 
 * `-e` _symbol_, `--entry`=_symbol_:
 
@@ -478,9 +432,6 @@ point symbol in a script.
 * `--Ttext`=_address_:
   Alias for `--section-start=.text=`_address_.
 
-* `--Ttext-segment`=_address_:
-  Set the address of the first byte of the text segment.
-
 * `--allow-multiple-definition`:
   Normally, the linker reports an error if there are more than one definition
   of a symbol. This option changes the default behavior so that it doesn't
@@ -529,14 +480,9 @@ point symbol in a script.
 * `--no-build-id`:
   Synonym for `--build-id=none`.
 
-* `--compress-debug-sections`=[ `zlib` | `zlib-gabi` | `zlib:`_N_ | `zstd` | `zstd:`_N_ | `none` ]:
+* `--compress-debug-sections`=[ `zlib` | `zlib-gabi` | `zstd` | `none` ]:
   Compress DWARF debug info (`.debug_*` sections) using the zlib or zstd
-  compression algorithm. `zlib-gabi` is an alias for `zlib`. `zlib:`_N_
-  selects the zlib compression level, where _N_ is between 0 and 9 (0
-  means no compression), and `zstd:`_N_ selects the zstd compression
-  level, where _N_ is between 1 and 22. Higher levels achieve better
-  compression ratios but are slower. `zlib` is equivalent to `zlib:1`
-  and `zstd` is equivalent to `zstd:3`.
+  compression algorithm. `zlib-gabi` is an alias for `zlib`.
 
 * `--defsym`=_symbol_=_value_:
   Define _symbol_ as an alias for _value_.
@@ -686,32 +632,16 @@ point symbol in a script.
   argument as percent-encoded, so you also need to escape all occurrences
   of `%` as `%25`.
 
-* `--pack-dyn-relocs`=[ `relr` | `android` | `android+relr` | `none` ]:
-  Compress dynamic relocations in the output file.
-
+* `--pack-dyn-relocs`=[ `relr` | `none` ]:
   If `relr` is specified, all `R_*_RELATIVE` relocations are put into
   `.relr.dyn` section instead of `.rel.dyn` or `.rela.dyn` section. Since
   `.relr.dyn` section uses a space-efficient encoding scheme, specifying this
   flag can reduce the size of the output. This is typically most effective for
   position-independent executable.
 
-  If `android` is specified, all dynamic relocations are encoded in Android's
-  packed relocation format (APS2) and stored in the `.rel.dyn` or `.rela.dyn`
-  section, whose section type is changed to `SHT_ANDROID_REL` or
-  `SHT_ANDROID_RELA`. The dynamic table is updated to use `DT_ANDROID_REL`
-  / `DT_ANDROID_RELA` and their `SZ` variants in place of the standard tags.
-
-  `android+relr` combines both: `R_*_RELATIVE` relocations go to `.relr.dyn`
-  and the rest are APS2-encoded. This is the configuration used by most
-  Android system binaries.
-
   Note that a runtime loader has to support `.relr.dyn` to run executables or
-  shared libraries linked with `--pack-dyn-relocs=relr`. As of 2026, glibc
-  (since 2.36), musl (since 1.2.4), Android, ChromeOS, and Fuchsia all
-  support it. The APS2 format, on the other hand, is only handled by
-  Android's bionic loader; the encoder itself is target-agnostic, but the
-  produced binary can only be loaded on platforms where bionic (or a
-  compatible loader) handles `DT_ANDROID_REL(A)`.
+  shared libraries linked with `--pack-dyn-relocs=relr`. As of 2022, only
+  ChromeOS, Android and Fuchsia support it.
 
 * `--pie`, `--pic-executable`, `--no-pie`, `--no-pic-executable`:
   Create a position-independent executable.
@@ -801,9 +731,6 @@ point symbol in a script.
   directory, it is searched from library search paths for the sake of
   compatibility with GNU ld.
 
-* `-w`, `--no-warnings`:
-  Suppress warnings and cancel `--fatal-warnings`.
-
 * `--warn-common`, `--no-warn-common`:
   Warn about common symbols.
 
@@ -901,15 +828,14 @@ point symbol in a script.
   segments with two different attributes.
 
   `separate-loadable-segments` adds paddings between segments with different
-  attributes so that they do not share the same page.
+  attributes so that they do not share the same page. This is the default.
 
   `separate-code` adds paddings only between executable and non-executable
   segments.
 
-  `noseparate-code` does not add any paddings between segments. This is the
-  default.
+  `noseparate-code` does not add any paddings between segments.
 
-* `-z defs`, `-z undefs`:
+* `-z defs`, `-z nodefs`:
   Report undefined symbols (even with `--shared`).
 
 * `-z shstk`:
@@ -918,14 +844,14 @@ point symbol in a script.
   Control-flow Enforcement Technology (CET), which is available since Tiger
   Lake (2020).
 
-* `-z start-stop-visibility`=[ `hidden` | `protected` ]:
+* `-z start_stop_visibility`=[ `hidden` | `protected` ]:
   If a section name is valid as a C identifier (i.e., it matches
   `/^[_a-zA-Z][_a-zA-Z0-9]*$/`), mold creates `__start_SECNAME` and
   `__stop_SECNAME` symbols to mark the beginning and end of the section,
   where `SECNAME` is the section name.
 
   You can make these marker symbols visible from other ELF modules by passing
-  `-z start-stop-visibility=protected`. Default is `hidden`.
+  `-z start_stop_visibility=protected`. Default is `hidden`.
 
 * `-z text`, `-z notext`, `-z textoff`:
   `mold` by default reports an error if dynamic relocations are created in

install-build-deps.sh

@@ -0,0 +1,52 @@
+#!/bin/sh
+# This script installs binary packages needed to build mold.
+# Feel free to send me a PR if your OS is not on this list.
+
+set -e
+. /etc/os-release
+
+set -x
+
+case "$ID" in
+ubuntu | pop | linuxmint | debian | raspbian | neon)
+  apt-get update
+  apt-get install -y cmake gcc g++ clang gdb
+  ;;
+fedora | amzn | rhel | centos)
+  dnf install -y gcc-g++ cmake glibc-static libstdc++-static diffutils util-linux tar
+  ;;
+rocky)
+  dnf install -y gcc-g++ cmake diffutils util-linux
+  ;;
+opensuse-*)
+  zypper install -y make cmake gcc-c++ glibc-devel-static tar diffutils util-linux
+  ;;
+gentoo)
+  emerge-webrsync
+  FEATURES='getbinpkg binpkg-request-signature' emerge dev-build/cmake
+  ;;
+arch | archarm | artix | endeavouros)
+  pacman -Sy --needed --noconfirm base-devel cmake util-linux
+  ;;
+void)
+  xbps-install -Sy xbps bash make cmake gcc tar diffutils util-linux
+  ;;
+alpine)
+  apk update
+  apk add bash make linux-headers cmake gcc g++
+  ;;
+clear-linux-os)
+  swupd update
+  swupd bundle-add c-basic diffutils
+  ;;
+almalinux)
+  dnf install -y gcc-toolset-13-gcc-c++ gcc-toolset-13-libstdc++-devel cmake diffutils
+  ;;
+freebsd)
+  pkg update
+  pkg install -y cmake bash binutils gcc
+  ;;
+*)
+  echo "Error: don't know anything about build dependencies on $ID-$VERSION_ID"
+  exit 1
+esac

install-cross-tools.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+set -e
+. /etc/os-release
+
+set -x
+
+# This script install packages for -DMOLD_ENABLE_QEMU_TESTS=1
+# to enable cross-target tests.
+#
+# Feel free to send me a PR if your OS is not on this list.
+
+case "$ID" in
+ubuntu | pop | linuxmint | debian | raspbian)
+  apt-get install -y qemu-user {gcc,g++}-{i686,aarch64,riscv64,powerpc,powerpc64,powerpc64le,s390x,sparc64,m68k,sh4,arc}-linux-gnu {gcc,g++}-arm-linux-gnueabihf
+  ;;
+*)
+  echo "Error: don't know anything about build dependencies on $ID-$VERSION_ID"
+  exit 1
+esac

install-mold.sh

@@ -1,31 +0,0 @@
-#!/bin/sh
-set -e
-
-PREFIX=${PREFIX:-/usr/local}
-MOLD_LIBDIR=${MOLD_LIBDIR:-$PREFIX/lib}
-
-srcdir=$(CDPATH= cd "$(dirname "$0")" && pwd)
-artifact_dir="${CARGO_TARGET_DIR:-$srcdir/target}/release"
-
-if [ ! -x "$artifact_dir/mold" ] ||
-  [ ! -f "$artifact_dir/mold-wrapper.so" ]; then
-  echo "install-mold.sh: release artifacts are missing" >&2
-  echo "Run 'cargo build --release' first." >&2
-  exit 1
-fi
-
-bindir="$DESTDIR$PREFIX/bin"
-libdir="$DESTDIR$MOLD_LIBDIR/mold"
-libexecdir="$DESTDIR$PREFIX/libexec/mold"
-mandir="$DESTDIR$PREFIX/share/man/man1"
-docdir="$DESTDIR$PREFIX/share/doc/mold"
-
-install -d "$bindir" "$libdir" "$libexecdir" "$mandir" "$docdir"
-install -m 755 "$artifact_dir/mold" "$bindir"
-install -m 755 "$artifact_dir/mold-wrapper.so" "$libdir"
-install -m 644 "$srcdir/docs/mold.1" "$mandir"
-install -m 644 "$srcdir/LICENSE" "$docdir"
-
-ln -sf mold "$bindir/ld.mold"
-ln -sf ../../bin/mold "$libexecdir/ld"
-ln -sf mold.1 "$mandir/ld.mold.1"

install-test-deps.sh

@@ -1,68 +0,0 @@
-#!/bin/sh
-# This script installs binary packages needed to test mold.
-# Feel free to send me a PR if your OS is not on this list.
-
-set -e
-. /etc/os-release
-
-set -x
-
-case "$ID" in
-ubuntu | pop | linuxmint | debian | raspbian | neon | zorin)
-  apt-get update
-  apt-get install -y curl gcc g++ clang gdb
-  apt-get install -y qemu-user \
-    gcc-i686-linux-gnu g++-i686-linux-gnu \
-    gcc-aarch64-linux-gnu g++-aarch64-linux-gnu \
-    gcc-riscv64-linux-gnu g++-riscv64-linux-gnu \
-    gcc-powerpc-linux-gnu g++-powerpc-linux-gnu \
-    gcc-powerpc64-linux-gnu g++-powerpc64-linux-gnu \
-    gcc-powerpc64le-linux-gnu g++-powerpc64le-linux-gnu \
-    gcc-s390x-linux-gnu g++-s390x-linux-gnu \
-    gcc-sparc64-linux-gnu g++-sparc64-linux-gnu \
-    gcc-m68k-linux-gnu g++-m68k-linux-gnu \
-    gcc-sh4-linux-gnu g++-sh4-linux-gnu \
-    gcc-arm-linux-gnueabihf g++-arm-linux-gnueabihf
-  ;;
-fedora | fedora-* | amzn | rhel | centos)
-  dnf install -y curl gcc-c++ glibc-static libstdc++-static diffutils util-linux tar
-  ;;
-rocky | ol)
-  dnf install -y curl gcc-c++ diffutils util-linux
-  ;;
-opensuse-*)
-  zypper install -y bash curl gcc-c++ glibc-devel-static tar diffutils util-linux gawk
-  ;;
-gentoo)
-  emerge-webrsync
-  FEATURES='getbinpkg binpkg-request-signature' emerge net-misc/curl
-  ;;
-arch | archarm | artix | endeavouros | manjaro | cachyos)
-  pacman -Sy --needed --noconfirm base-devel curl util-linux
-  ;;
-void)
-  xbps-install -Sy xbps bash curl gcc tar diffutils util-linux
-  ;;
-alpine)
-  apk update
-  apk add bash curl linux-headers gcc g++
-  ;;
-clear-linux-os)
-  swupd update
-  swupd bundle-add c-basic diffutils
-  ;;
-almalinux)
-  dnf install -y curl gcc-toolset-13-gcc-c++ gcc-toolset-13-libstdc++-devel diffutils
-  ;;
-altlinux)
-  apt-get update
-  apt-get install -y curl gcc-c++ diffutils util-linux
-  ;;
-freebsd)
-  pkg update
-  pkg install -y bash binutils curl gcc
-  ;;
-*)
-  echo "Error: don't know anything about test dependencies on $ID-$VERSION_ID"
-  exit 1
-esac

lib/archive-file.h

@@ -0,0 +1,173 @@
+// This file contains functions to read an archive file (.a file).
+// An archive file is just a bundle of object files. It's similar to
+// tar or zip, but the contents are not compressed.
+//
+// An archive file is either "regular" or "thin". A regular archive
+// contains object files directly, while a thin archive contains only
+// pathnames. In the latter case, actual file contents have to be read
+// from given pathnames. A regular archive is sometimes called "fat"
+// archive as opposed to "thin".
+//
+// If an archive file is given to the linker, the linker pulls out
+// object files that are needed to resolve undefined symbols. So,
+// bunding object files as an archive and giving that archive to the
+// linker has a different meaning than directly giving the same set of
+// object files to the linker. The former links only needed object
+// files, while the latter links all the given object files.
+//
+// Therefore, if you link libc.a for example, not all the libc
+// functions are linked to your binary. Instead, only object files
+// that provides functions and variables used in your program get
+// linked. To make this efficient, static library functions are
+// usually separated to each object file in an archive file. You can
+// see the contents of libc.a by running `ar t
+// /usr/lib/x86_64-linux-gnu/libc.a`.
+
+#pragma once
+
+#include "common.h"
+
+namespace mold {
+
+struct ArHdr {
+  char ar_name[16];
+  char ar_date[12];
+  char ar_uid[6];
+  char ar_gid[6];
+  char ar_mode[8];
+  char ar_size[10];
+  char ar_fmag[2];
+
+  bool starts_with(std::string_view s) const {
+    return std::string_view(ar_name, s.size()) == s;
+  }
+
+  bool is_strtab() const {
+    return starts_with("// ");
+  }
+
+  bool is_symtab() const {
+    return starts_with("/ ") || starts_with("/SYM64/ ");
+  }
+
+  std::string read_name(std::string_view strtab, u8 *&ptr) const {
+    // BSD-style long filename
+    if (starts_with("#1/")) {
+      int namelen = atoi(ar_name + 3);
+      std::string name{(char *)ptr, (size_t)namelen};
+      ptr += namelen;
+
+      if (size_t pos = name.find('\0'))
+        name = name.substr(0, pos);
+      return name;
+    }
+
+    // SysV-style long filename
+    if (starts_with("/")) {
+      const char *start = strtab.data() + atoi(ar_name + 1);
+      return {start, (const char *)strstr(start, "/\n")};
+    }
+
+    // Short fileanme
+    if (const char *end = (char *)memchr(ar_name, '/', sizeof(ar_name)))
+      return {ar_name, end};
+    return {ar_name, sizeof(ar_name)};
+  }
+};
+
+template <typename Context>
+std::vector<MappedFile *>
+read_thin_archive_members(Context &ctx, MappedFile *mf) {
+  u8 *begin = mf->data;
+  u8 *data = begin + 8;
+  std::vector<MappedFile *> vec;
+  std::string_view strtab;
+
+  while (data < begin + mf->size) {
+    // Each header is aligned to a 2 byte boundary.
+    if ((begin - data) % 2)
+      data++;
+
+    ArHdr &hdr = *(ArHdr *)data;
+    u8 *body = data + sizeof(hdr);
+    u64 size = atol(hdr.ar_size);
+
+    // Read a string table.
+    if (hdr.is_strtab()) {
+      strtab = {(char *)body, (size_t)size};
+      data = body + size;
+      continue;
+    }
+
+    // Skip a symbol table.
+    if (hdr.is_symtab()) {
+      data = body + size;
+      continue;
+    }
+
+    if (!hdr.starts_with("#1/") && !hdr.starts_with("/"))
+      Fatal(ctx) << mf->name << ": filename is not stored as a long filename";
+
+    std::string name = hdr.read_name(strtab, body);
+
+    // Skip if symbol table
+    if (name == "__.SYMDEF" || name == "__.SYMDEF SORTED")
+      continue;
+
+    std::string path = name.starts_with('/') ?
+      name : (path_dirname(mf->name) / name).string();
+    vec.push_back(must_open_file(ctx, path));
+    vec.back()->thin_parent = mf;
+    data = body;
+  }
+  return vec;
+}
+
+template <typename Context>
+std::vector<MappedFile *> read_fat_archive_members(Context &ctx, MappedFile *mf) {
+  u8 *begin = mf->data;
+  u8 *data = begin + 8;
+  std::vector<MappedFile *> vec;
+  std::string_view strtab;
+
+  while (begin + mf->size - data >= 2) {
+    if ((begin - data) % 2)
+      data++;
+
+    ArHdr &hdr = *(ArHdr *)data;
+    u8 *body = data + sizeof(hdr);
+    u64 size = atol(hdr.ar_size);
+    data = body + size;
+
+    // Read if string table
+    if (hdr.is_strtab()) {
+      strtab = {(char *)body, (size_t)size};
+      continue;
+    }
+
+    // Skip if symbol table
+    if (hdr.is_symtab())
+      continue;
+
+    // Read the name field
+    std::string name = hdr.read_name(strtab, body);
+
+    // Skip if symbol table
+    if (name == "__.SYMDEF" || name == "__.SYMDEF SORTED")
+      continue;
+
+    vec.push_back(mf->slice(ctx, name, body - begin, data - body));
+  }
+  return vec;
+}
+
+template <typename Context>
+std::vector<MappedFile *> read_archive_members(Context &ctx, MappedFile *mf) {
+  std::string_view str = mf->get_contents();
+  if (str.starts_with("!<arch>\n"))
+    return read_fat_archive_members(ctx, mf);
+  assert(str.starts_with("!<thin>\n"));
+  return read_thin_archive_members(ctx, mf);
+}
+
+} // namespace mold

lib/common.h

@@ -0,0 +1,979 @@
+#pragma once
+
+#include "config.h"
+#include "integers.h"
+
+#include <array>
+#include <atomic>
+#include <bit>
+#include <bitset>
+#include <cassert>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <fcntl.h>
+#include <filesystem>
+#include <iostream>
+#include <mutex>
+#include <optional>
+#include <span>
+#include <sstream>
+#include <string>
+#include <string_view>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <tbb/concurrent_vector.h>
+#include <tbb/enumerable_thread_specific.h>
+#include <tbb/parallel_for.h>
+#include <vector>
+
+#ifdef _WIN32
+# include <io.h>
+#else
+# include <sys/mman.h>
+# include <unistd.h>
+#endif
+
+#define XXH_INLINE_ALL 1
+#include "../third-party/xxhash/xxhash.h"
+
+#ifdef NDEBUG
+# define unreachable() __builtin_unreachable()
+#else
+# define unreachable() assert(0 && "unreachable")
+#endif
+
+inline uint64_t hash_string(std::string_view str) {
+  return XXH3_64bits(str.data(), str.size());
+}
+
+class HashCmp {
+public:
+  static size_t hash(const std::string_view &k) {
+    return hash_string(k);
+  }
+
+  static bool equal(const std::string_view &k1, const std::string_view &k2) {
+    return k1 == k2;
+  }
+};
+
+namespace mold {
+
+namespace ranges = std::ranges;
+using namespace std::literals::string_literals;
+using namespace std::literals::string_view_literals;
+
+inline char *output_tmpfile;
+
+inline u8 *output_buffer_start = nullptr;
+inline u8 *output_buffer_end = nullptr;
+
+extern std::string mold_git_hash;
+
+std::string errno_string();
+void cleanup();
+void install_signal_handler();
+
+inline u64 combine_hash(u64 a, u64 b) {
+  return a ^ (b + 0x9e3779b9 + (a << 6) + (a >> 2));
+}
+
+//
+// Error output
+//
+
+// Some C++ stdlibs don't support std::osyncstream even though
+// it's is in the C++20 standard. So we implement it ourselves.
+class SyncStream {
+public:
+  SyncStream(std::ostream &out) : out(out) {}
+
+  ~SyncStream() {
+    emit();
+  }
+
+  template <typename T> SyncStream &operator<<(T &&val) {
+    ss << std::forward<T>(val);
+    return *this;
+  }
+
+  void emit() {
+    if (emitted)
+      return;
+
+    std::scoped_lock lock(mu);
+    out << ss.str() << '\n';
+    emitted = true;
+  }
+
+private:
+  std::ostream &out;
+  std::stringstream ss;
+  bool emitted = false;
+  static inline std::mutex mu;
+};
+
+template <typename Context>
+class Out {
+public:
+  Out(Context &ctx) {}
+
+  template <typename T> Out &operator<<(T &&val) {
+    out << std::forward<T>(val);
+    return *this;
+  }
+
+private:
+  SyncStream out{std::cout};
+};
+
+static std::string_view fatal_mono = "mold: fatal: ";
+static std::string_view fatal_color = "mold: \033[0;1;31mfatal:\033[0m ";
+static std::string_view error_mono = "mold: error: ";
+static std::string_view error_color = "mold: \033[0;1;31merror:\033[0m ";
+static std::string_view warning_mono = "mold: warning: ";
+static std::string_view warning_color = "mold: \033[0;1;35mwarning:\033[0m ";
+
+template <typename Context>
+class Fatal {
+public:
+  Fatal(Context &ctx) {
+    out << (ctx.arg.color_diagnostics ? fatal_color : fatal_mono);
+  }
+
+  [[noreturn]] ~Fatal() {
+    out.emit();
+    cleanup();
+    _exit(1);
+  }
+
+  template <typename T> Fatal &operator<<(T &&val) {
+    out << std::forward<T>(val);
+    return *this;
+  }
+
+private:
+  SyncStream out{std::cerr};
+};
+
+template <typename Context>
+class Error {
+public:
+  Error(Context &ctx) {
+    if (ctx.arg.noinhibit_exec) {
+      out << (ctx.arg.color_diagnostics ? warning_color : warning_mono);
+    } else {
+      out << (ctx.arg.color_diagnostics ? error_color : error_mono);
+      ctx.has_error = true;
+    }
+  }
+
+  template <typename T> Error &operator<<(T &&val) {
+    out << std::forward<T>(val);
+    return *this;
+  }
+
+private:
+  SyncStream out{std::cerr};
+};
+
+template <typename Context>
+class Warn {
+public:
+  Warn(Context &ctx) {
+    if (ctx.arg.suppress_warnings)
+      return;
+
+    out.emplace(std::cerr);
+
+    if (ctx.arg.fatal_warnings) {
+      *out << (ctx.arg.color_diagnostics ? error_color : error_mono);
+      ctx.has_error = true;
+    } else {
+      *out << (ctx.arg.color_diagnostics ? warning_color : warning_mono);
+    }
+  }
+
+  template <typename T> Warn &operator<<(T &&val) {
+    if (out)
+      *out << std::forward<T>(val);
+    return *this;
+  }
+
+private:
+  std::optional<SyncStream> out;
+};
+
+//
+// Atomics
+//
+
+// This is the same as std::atomic except that the default memory
+// order is relaxed instead of sequential consistency.
+template <typename T>
+struct Atomic : std::atomic<T> {
+  static constexpr std::memory_order relaxed = std::memory_order_relaxed;
+
+  using std::atomic<T>::atomic;
+
+  Atomic(const Atomic<T> &other) : std::atomic<T>(other.load()) {}
+
+  Atomic<T> &operator=(const Atomic<T> &other) {
+    store(other.load());
+    return *this;
+  }
+
+  void operator=(T val) { store(val); }
+  operator T() const { return load(); }
+
+  void store(T val, std::memory_order order = relaxed) {
+    std::atomic<T>::store(val, order);
+  }
+
+  T load(std::memory_order order = relaxed) const {
+    return std::atomic<T>::load(order);
+  }
+
+  T exchange(T val) { return std::atomic<T>::exchange(val, relaxed); }
+  T operator|=(T val) { return std::atomic<T>::fetch_or(val, relaxed); }
+  T operator++() { return std::atomic<T>::fetch_add(1, relaxed) + 1; }
+  T operator--() { return std::atomic<T>::fetch_sub(1, relaxed) - 1; }
+  T operator++(int) { return std::atomic<T>::fetch_add(1, relaxed); }
+  T operator--(int) { return std::atomic<T>::fetch_sub(1, relaxed); }
+
+  bool test_and_set() {
+    // A relaxed load + branch (assuming miss) takes only around 20 cycles,
+    // while an atomic RMW can easily take hundreds on x86. We note that it's
+    // common that another thread beat us in marking, so doing an optimistic
+    // early test tends to improve performance in the ~20% ballpark.
+    return load() || exchange(true);
+  }
+};
+
+//
+// mimalloc.cc
+//
+
+void set_mimalloc_options();
+
+//
+// perf.cc
+//
+
+// Counter is used to collect statistics numbers.
+class Counter {
+public:
+  Counter(std::string_view name, i64 value = 0) : name(name), values(value) {
+    static std::mutex mu;
+    std::scoped_lock lock(mu);
+    instances.push_back(this);
+  }
+
+  Counter &operator++(int) {
+    if (enabled) [[unlikely]]
+      values.local()++;
+    return *this;
+  }
+
+  Counter &operator+=(int delta) {
+    if (enabled) [[unlikely]]
+      values.local() += delta;
+    return *this;
+  }
+
+  static void print();
+
+  static inline bool enabled = false;
+
+private:
+  i64 get_value();
+
+  std::string_view name;
+  tbb::enumerable_thread_specific<i64> values;
+
+  static inline std::vector<Counter *> instances;
+};
+
+// Timer and TimeRecord records elapsed time (wall clock time)
+// used by each pass of the linker.
+struct TimerRecord {
+  TimerRecord(std::string name, TimerRecord *parent = nullptr);
+  void stop();
+
+  std::string name;
+  TimerRecord *parent;
+  tbb::concurrent_vector<TimerRecord *> children;
+  i64 start;
+  i64 end;
+  i64 user;
+  i64 sys;
+  bool stopped = false;
+};
+
+void
+print_timer_records(tbb::concurrent_vector<std::unique_ptr<TimerRecord>> &);
+
+template <typename Context>
+class Timer {
+public:
+  Timer(Context &ctx, std::string name, Timer *parent = nullptr) {
+    record = new TimerRecord(name, parent ? parent->record : nullptr);
+    ctx.timer_records.emplace_back(record);
+  }
+
+  Timer(const Timer &) = delete;
+
+  ~Timer() {
+    record->stop();
+  }
+
+  void stop() {
+    record->stop();
+  }
+
+private:
+  TimerRecord *record;
+};
+
+//
+// Utility functions
+//
+
+// Some C++ libraries haven't implemented std::has_single_bit yet.
+inline bool has_single_bit(u64 val) {
+  return std::popcount(val) == 1;
+}
+
+// Some C++ libraries haven't implemented std::bit_ceil yet.
+inline u64 bit_ceil(u64 val) {
+  if (has_single_bit(val))
+    return val;
+  return 1LL << (64 - std::countl_zero(val));
+}
+
+inline u64 align_to(u64 val, u64 align) {
+  if (align == 0)
+    return val;
+  assert(has_single_bit(align));
+  return (val + align - 1) & ~(align - 1);
+}
+
+inline u64 align_down(u64 val, u64 align) {
+  assert(has_single_bit(align));
+  return val & ~(align - 1);
+}
+
+inline u64 bit(u64 val, i64 pos) {
+  return (val >> pos) & 1;
+};
+
+// Returns [hi:lo] bits of val.
+inline u64 bits(u64 val, u64 hi, u64 lo) {
+  return (val >> lo) & ((1LL << (hi - lo + 1)) - 1);
+}
+
+// Cast val to a signed N bit integer.
+// For example, sign_extend(x, 32) == (i32)x for any integer x.
+inline i64 sign_extend(u64 val, i64 n) {
+  return (i64)(val << (64 - n)) >> (64 - n);
+}
+
+inline bool is_int(u64 val, i64 n) {
+  return sign_extend(val, n) == val;
+}
+
+template <typename T, typename Compare = std::less<T>>
+void update_minimum(std::atomic<T> &atomic, u64 new_val, Compare cmp = {}) {
+  T old_val = atomic.load(std::memory_order_relaxed);
+  while (cmp(new_val, old_val) &&
+         !atomic.compare_exchange_weak(old_val, new_val,
+                                       std::memory_order_relaxed));
+}
+
+template <typename T, typename Compare = std::less<T>>
+void update_maximum(std::atomic<T> &atomic, u64 new_val, Compare cmp = {}) {
+  T old_val = atomic.load(std::memory_order_relaxed);
+  while (cmp(old_val, new_val) &&
+         !atomic.compare_exchange_weak(old_val, new_val,
+                                       std::memory_order_relaxed));
+}
+
+template <typename T>
+inline void append(std::vector<T> &x, const auto &y) {
+  x.insert(x.end(), y.begin(), y.end());
+}
+
+template <typename T>
+inline std::vector<T> flatten(std::vector<std::vector<T>> &vec) {
+  i64 size = 0;
+  for (std::vector<T> &v : vec)
+    size += v.size();
+
+  std::vector<T> ret;
+  ret.reserve(size);
+  for (std::vector<T> &v : vec)
+    append(ret, v);
+  return ret;
+}
+
+template <typename T>
+inline void remove_duplicates(std::vector<T> &vec) {
+  vec.erase(std::unique(vec.begin(), vec.end()), vec.end());
+}
+
+inline i64 write_string(void *buf, std::string_view str) {
+  memcpy(buf, str.data(), str.size());
+  *((u8 *)buf + str.size()) = '\0';
+  return str.size() + 1;
+}
+
+template <typename T>
+inline void write_vector(void *buf, const std::vector<T> &vec) {
+  if (!vec.empty())
+    memcpy(buf, vec.data(), vec.size() * sizeof(T));
+}
+
+inline void encode_uleb(std::vector<u8> &vec, u64 val) {
+  do {
+    u8 byte = val & 0x7f;
+    val >>= 7;
+    vec.push_back(val ? (byte | 0x80) : byte);
+  } while (val);
+}
+
+inline void encode_sleb(std::vector<u8> &vec, i64 val) {
+  for (;;) {
+    u8 byte = val & 0x7f;
+    val >>= 7;
+
+    bool neg = (byte & 0x40);
+    if ((val == 0 && !neg) || (val == -1 && neg)) {
+      vec.push_back(byte);
+      break;
+    }
+    vec.push_back(byte | 0x80);
+  }
+}
+
+inline i64 write_uleb(u8 *buf, u64 val) {
+  i64 i = 0;
+  do {
+    u8 byte = val & 0x7f;
+    val >>= 7;
+    buf[i++] = val ? (byte | 0x80) : byte;
+  } while (val);
+  return i;
+}
+
+inline u64 read_uleb(u8 **buf) {
+  u64 val = 0;
+  u8 shift = 0;
+  u8 byte;
+  do {
+    byte = *(*buf)++;
+    val |= (byte & 0x7f) << shift;
+    shift += 7;
+  } while (byte & 0x80);
+  return val;
+}
+
+inline u64 read_uleb(u8 *buf) {
+  u8 *tmp = buf;
+  return read_uleb(&tmp);
+}
+
+inline i64 read_sleb(u8 **buf) {
+  u64 val = 0;
+  u8 shift = 0;
+  u8 byte;
+  do {
+    byte = *(*buf)++;
+    val |= (byte & 0x7f) << shift;
+    shift += 7;
+  } while (byte & 0x80);
+  return sign_extend(val, shift);
+}
+
+inline i64 read_sleb(u8 *buf) {
+  u8 *tmp = buf;
+  return read_sleb(&tmp);
+}
+
+inline u64 read_uleb(std::string_view *str) {
+  u8 *start = (u8 *)str->data();
+  u8 *ptr = start;
+  u64 val = read_uleb(&ptr);
+  *str = str->substr(ptr - start);
+  return val;
+}
+
+inline u64 read_uleb(std::string_view str) {
+  std::string_view tmp = str;
+  return read_uleb(&tmp);
+}
+
+inline i64 uleb_size(u64 val) {
+  for (int i = 1; i < 9; i++)
+    if (val < (1LL << (7 * i)))
+      return i;
+  return 9;
+}
+
+inline void overwrite_uleb(u8 *loc, u64 val) {
+  while (*loc & 0b1000'0000) {
+    *loc++ = 0b1000'0000 | (val & 0b0111'1111);
+    val >>= 7;
+  }
+  *loc = val & 0b0111'1111;
+}
+
+static inline void pause() {
+#if defined(__x86_64__)
+  asm volatile("pause");
+#elif defined(__aarch64__)
+  asm volatile("yield");
+#elif defined(__ARM_ARCH_7A__) || defined(__ARM_ARCH_8A__)
+  asm volatile("yield");
+#endif
+}
+
+//
+// Concurrent Map
+//
+
+// This is an implementation of a fast concurrent hash map. Unlike
+// ordinary hash tables, this impl just aborts if it becomes full.
+// So you need to give a correct estimation of the final size before
+// using it. We use this hash map to uniquify pieces of data in
+// mergeable sections.
+//
+// We've implemented this ourselves because the performance of
+// conrurent hash map is critical for our linker.
+template <typename T>
+class ConcurrentMap {
+public:
+  ConcurrentMap() = default;
+
+  ConcurrentMap(i64 nbuckets) {
+    resize(nbuckets);
+  }
+
+  ~ConcurrentMap() {
+    if (entries) {
+#ifdef _WIN32
+      _aligned_free(entries);
+#else
+      munmap(entries, sizeof(Entry) * nbuckets);
+#endif
+    }
+  }
+
+  // In order to avoid unnecessary cache-line false sharing, we want
+  // to make this object to be aligned to a reasonably large
+  // power-of-two address.
+  struct alignas(32) Entry {
+    Atomic<const char *> key;
+    u32 keylen;
+    T value;
+  };
+
+  void resize(i64 nbuckets) {
+    assert(!entries);
+    this->nbuckets = std::max<i64>(MIN_NBUCKETS, bit_ceil(nbuckets));
+    i64 bufsize = sizeof(Entry) * this->nbuckets;
+
+    // Allocate a zero-initialized buffer. We use mmap() if available
+    // because it's faster than malloc() and memset().
+#ifdef _WIN32
+    entries = (Entry *)_aligned_malloc(bufsize, alignof(Entry));
+    memset((void *)entries, 0, bufsize);
+#else
+    entries = (Entry *)mmap(nullptr, bufsize, PROT_READ | PROT_WRITE,
+                            MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+#endif
+  }
+
+  std::pair<T *, bool> insert(std::string_view key, u64 hash, const T &val) {
+    assert(has_single_bit(nbuckets));
+
+    u64 begin = hash & (nbuckets - 1);
+    u64 mask = nbuckets / NUM_SHARDS - 1;
+
+    for (i64 i = 0; i < MAX_RETRY; i++) {
+      u64 idx = (begin & ~mask) | ((begin + i) & mask);
+      Entry &ent = entries[idx];
+
+      // It seems avoiding compare-and-swap is faster overall at least
+      // on my Zen4 machine, so do it.
+      if (const char *ptr = ent.key.load(std::memory_order_acquire);
+          ptr != nullptr && ptr != (char *)-1) {
+        if (key == std::string_view(ptr, ent.keylen))
+          return {&ent.value, false};
+        continue;
+      }
+
+      // Otherwise, use CAS to atomically claim the ownership of the slot.
+      const char *ptr = nullptr;
+      bool claimed = ent.key.compare_exchange_strong(ptr, (char *)-1,
+                                                     std::memory_order_acquire);
+
+      // If we successfully claimed the ownership of the slot,
+      // copy values to it.
+      if (claimed) {
+        new (&ent.value) T(val);
+        ent.keylen = key.size();
+        ent.key.store(key.data(), std::memory_order_release);
+        return {&ent.value, true};
+      }
+
+      // If someone is copying values to the slot, do busy wait.
+      while (ptr == (char *)-1) {
+        pause();
+        ptr = ent.key.load(std::memory_order_acquire);
+      }
+
+      // If the same key is already present, this is the slot we are
+      // looking for.
+      if (key == std::string_view(ptr, ent.keylen))
+        return {&ent.value, false};
+    }
+
+    std::cerr << "ConcurrentMap is full\n";
+    abort();
+  }
+
+  i64 get_idx(T *value) const {
+    uintptr_t addr = (uintptr_t)value - (uintptr_t)value % sizeof(Entry);
+    return (Entry *)addr - entries;
+  }
+
+  // Return a list of map entries sorted in a deterministic order.
+  std::vector<Entry *> get_sorted_entries(i64 shard_idx) {
+    if (nbuckets == 0)
+      return {};
+
+    i64 shard_size = nbuckets / NUM_SHARDS;
+    i64 begin = shard_idx * shard_size;
+    i64 end = begin + shard_size;
+
+    i64 sz = 0;
+    for (i64 i = begin; i < end; i++)
+      if (entries[i].key)
+        sz++;
+
+    std::vector<Entry *> vec;
+    vec.reserve(sz);
+
+    // Since the shard is circular, we need to handle the last entries
+    // as if they were next to the first entries.
+    while (entries[end - 1].key)
+      vec.push_back(entries + --end);
+
+    // Find entries contiguous in the buckets and sort them.
+    i64 last = 0;
+    for (i64 i = begin; i < end;) {
+      while (i < end && entries[i].key)
+        vec.push_back(entries + i++);
+
+      std::sort(vec.begin() + last, vec.end(), [](Entry *a, Entry *b) {
+        if (a->keylen != b->keylen)
+          return a->keylen < b->keylen;
+        return memcmp(a->key, b->key, a->keylen) < 0;
+      });
+
+      last = vec.size();
+
+      while (i < end && !entries[i].key)
+        i++;
+    }
+    return vec;
+  }
+
+  std::vector<Entry *> get_sorted_entries_all() {
+    std::vector<std::vector<Entry *>> vec(NUM_SHARDS);
+    tbb::parallel_for((i64)0, NUM_SHARDS, [&](i64 i) {
+      vec[i] = get_sorted_entries(i);
+    });
+    return flatten(vec);
+  }
+
+  static constexpr i64 MIN_NBUCKETS = 4096;
+  static constexpr i64 NUM_SHARDS = 16;
+  static constexpr i64 MAX_RETRY = 256;
+
+  Entry *entries = nullptr;
+  u64 nbuckets = 0;
+};
+
+//
+// random.cc
+//
+
+void get_random_bytes(u8 *buf, i64 size);
+
+//
+// hyperloglog.cc
+//
+
+class HyperLogLog {
+public:
+  void insert(u64 hash) {
+    update_maximum(buckets[hash & (NBUCKETS - 1)], std::countl_zero(hash) + 1);
+  }
+
+  i64 get_cardinality() const;
+
+  void merge(const HyperLogLog &other) {
+    for (i64 i = 0; i < NBUCKETS; i++)
+      update_maximum(buckets[i], other.buckets[i]);
+  }
+
+private:
+  static constexpr i64 NBUCKETS = 2048;
+  static constexpr double ALPHA = 0.79402;
+
+  Atomic<u8> buckets[NBUCKETS];
+};
+
+//
+// glob.cc
+//
+
+class Glob {
+  typedef enum { STRING, STAR, QUESTION, BRACKET } Kind;
+
+  struct Element {
+    Element(Kind k) : kind(k) {}
+    Kind kind;
+    std::string str;
+    std::bitset<256> bitset;
+  };
+
+public:
+  static std::optional<Glob> compile(std::string_view pat);
+  bool match(std::string_view str);
+
+private:
+  Glob(std::vector<Element> &&vec) : elements(vec) {}
+  static bool do_match(std::string_view str, std::span<Element> elements);
+
+  std::vector<Element> elements;
+};
+
+//
+// multi-glob.cc
+//
+
+class MultiGlob {
+public:
+  bool add(std::string_view pat, i64 val);
+  bool empty() const { return strings.empty(); }
+  std::optional<i64> find(std::string_view str);
+
+private:
+  struct TrieNode {
+    i64 value = -1;
+    TrieNode *suffix_link = nullptr;
+    std::unique_ptr<TrieNode> children[256];
+  };
+
+  void compile();
+  void fix_suffix_links(TrieNode &node);
+  void fix_values();
+  i64 find_aho_corasick(std::string_view str);
+
+  std::vector<std::string> strings;
+  std::unique_ptr<TrieNode> root;
+  std::vector<std::pair<Glob, i64>> globs;
+  std::once_flag once;
+  bool is_compiled = false;
+  bool prefix_match = false;
+};
+
+//
+// filepath.cc
+//
+
+inline std::filesystem::path path_dirname(std::string_view path) {
+  return std::filesystem::path(path).parent_path();
+}
+
+inline std::string path_filename(std::string_view path) {
+  return std::filesystem::path(path).filename().string();
+}
+
+inline std::string path_clean(std::string_view path) {
+  return std::filesystem::path(path).lexically_normal().string();
+}
+
+std::string get_self_path();
+
+//
+// demangle.cc
+//
+
+std::optional<std::string_view> demangle_cpp(std::string_view name);
+std::optional<std::string_view> demangle_rust(std::string_view name);
+
+//
+// jbos.cc
+//
+
+void acquire_global_lock();
+void release_global_lock();
+
+//
+// crc32.cc
+//
+
+u32 compute_crc32(u32 crc, u8 *buf, i64 len);
+std::vector<u8> crc32_solve(u32 current, u32 desired);
+
+//
+// compress.cc
+//
+
+class Compressor {
+public:
+  virtual void write_to(u8 *buf) = 0;
+  virtual ~Compressor() {}
+  i64 compressed_size = 0;
+};
+
+class ZlibCompressor : public Compressor {
+public:
+  ZlibCompressor(u8 *buf, i64 size);
+  void write_to(u8 *buf) override;
+
+private:
+  std::vector<std::vector<u8>> shards;
+  u64 checksum = 0;
+};
+
+class ZstdCompressor : public Compressor {
+public:
+  ZstdCompressor(u8 *buf, i64 size);
+  void write_to(u8 *buf) override;
+
+private:
+  std::vector<std::vector<u8>> shards;
+};
+
+//
+// tar.cc
+//
+
+// TarFile is a class to create a tar file.
+//
+// If you pass `--repro` to mold, mold collects all input files and
+// put them into `<output-file-path>.repro.tar`, so that it is easy to
+// run the same command with the same command line arguments.
+class TarWriter {
+public:
+  static std::unique_ptr<TarWriter>
+  open(std::string output_path, std::string basedir);
+
+  ~TarWriter();
+  void append(std::string path, std::string_view data);
+
+private:
+  TarWriter(FILE *out, std::string basedir) : out(out), basedir(basedir) {}
+
+  FILE *out = nullptr;
+  std::string basedir;
+};
+
+//
+// Memory-mapped file
+//
+
+// MappedFile represents an mmap'ed input file.
+// mold uses mmap-IO only.
+class MappedFile {
+public:
+  ~MappedFile() { unmap(); }
+  void unmap();
+  void close_fd();
+  void reopen_fd(const std::string &path);
+
+  template <typename Context>
+  MappedFile *slice(Context &ctx, std::string name, u64 start, u64 size) {
+    MappedFile *mf = new MappedFile;
+    mf->name = name;
+    mf->data = data + start;
+    mf->size = size;
+    mf->parent = this;
+
+    ctx.mf_pool.emplace_back(mf);
+    return mf;
+  }
+
+  std::string_view get_contents() {
+    return std::string_view((char *)data, size);
+  }
+
+  i64 get_offset() const {
+    return parent ? (data - parent->data + parent->get_offset()) : 0;
+  }
+
+  // Returns a string that uniquely identify a file that is possibly
+  // in an archive.
+  std::string get_identifier() const {
+    if (parent) {
+      // We use the file offset within an archive as an identifier
+      // because archive members may have the same name.
+      return parent->name + ":" + std::to_string(get_offset());
+    }
+
+    if (thin_parent) {
+      // If this is a thin archive member, the filename part is
+      // guaranteed to be unique.
+      return thin_parent->name + ":" + name;
+    }
+    return name;
+  }
+
+  std::string name;
+  u8 *data = nullptr;
+  i64 size = 0;
+  bool given_fullpath = true;
+  MappedFile *parent = nullptr;
+  MappedFile *thin_parent = nullptr;
+
+  // For --dependency-file
+  bool is_dependency = true;
+
+#ifdef _WIN32
+  HANDLE fd = INVALID_HANDLE_VALUE;
+#else
+  int fd = -1;
+#endif
+};
+
+MappedFile *open_file_impl(const std::string &path, std::string &error);
+
+template <typename Context>
+MappedFile *open_file(Context &ctx, std::string path) {
+  if (path.starts_with('/') && !ctx.arg.chroot.empty())
+    path = ctx.arg.chroot + "/" + path_clean(path);
+
+  std::string error;
+  MappedFile *mf = open_file_impl(path, error);
+  if (!error.empty())
+    Fatal(ctx) << error;
+
+  if (mf)
+    ctx.mf_pool.emplace_back(mf);
+  return mf;
+}
+
+template <typename Context>
+MappedFile *must_open_file(Context &ctx, std::string path) {
+  MappedFile *mf = open_file(ctx, path);
+  if (!mf)
+    Fatal(ctx) << "cannot open " << path << ": " << errno_string();
+  return mf;
+}
+
+} // namespace mold

lib/compress.cc

@@ -0,0 +1,185 @@
+// This file implements a multi-threaded zlib and zstd compression
+// routine.
+//
+// zlib-compressed data can be merged just by concatenation as long as
+// each piece of data is flushed with Z_SYNC_FLUSH. In this file, we
+// split input data into multiple shards, compress them individually
+// and concatenate them. We then append a header, a trailer and a
+// checksum so that the concatenated data is valid zlib-format data.
+//
+// zstd-compressed data can be merged in the same way.
+//
+// Using threads to compress data has a downside. Since the dictionary
+// is reset on boundaries of shards, compression ratio is sacrificed
+// a little bit. However, if a shard size is large enough, that loss
+// is negligible in practice.
+
+#include "common.h"
+
+#include <tbb/parallel_for_each.h>
+#include <zlib.h>
+#include <zstd.h>
+
+#define CHECK(fn)                               \
+  do {                                          \
+    [[maybe_unused]] int r = (fn);              \
+    assert(r == Z_OK);                          \
+  } while (0)
+
+namespace mold {
+
+static constexpr i64 SHARD_SIZE = 1024 * 1024;
+
+static std::vector<std::string_view> split(std::string_view input) {
+  std::vector<std::string_view> shards;
+
+  while (input.size() >= SHARD_SIZE) {
+    shards.push_back(input.substr(0, SHARD_SIZE));
+    input = input.substr(SHARD_SIZE);
+  }
+  if (!input.empty())
+    shards.push_back(input);
+  return shards;
+}
+
+static std::vector<u8> zlib_compress(std::string_view input) {
+  // Initialize zlib stream. Since debug info is generally compressed
+  // pretty well with lower compression levels, we chose compression
+  // level 1.
+  z_stream strm;
+  strm.zalloc = Z_NULL;
+  strm.zfree = Z_NULL;
+  strm.opaque = Z_NULL;
+
+  CHECK(deflateInit2(&strm, 1, Z_DEFLATED, -15, 8, Z_DEFAULT_STRATEGY));
+
+  // Set an input buffer
+  strm.avail_in = input.size();
+  strm.next_in = (u8 *)input.data();
+
+  // Set an output buffer. deflateBound() returns an upper bound
+  // on the compression size. +16 for Z_SYNC_FLUSH.
+  std::vector<u8> buf(deflateBound(&strm, strm.avail_in) + 16);
+
+  // Compress data. It writes all compressed bytes except the last
+  // partial byte, so up to 7 bits can be held to be written to the
+  // buffer.
+  strm.avail_out = buf.size();
+  strm.next_out = buf.data();
+  CHECK(deflate(&strm, Z_BLOCK));
+
+  // This is a workaround for libbacktrace before 2022-04-06.
+  //
+  // Zlib is a bit stream, and what Z_SYNC_FLUSH does is to write a
+  // three bit value indicating the start of an uncompressed data
+  // block followed by four byte data 00 00 ff ff which indicates that
+  // the length of the block is zero. libbacktrace uses its own zlib
+  // inflate routine, and it had a bug that if that particular three
+  // bit value happens to end at a byte boundary, it accidentally
+  // skipped the next byte.
+  //
+  // In order to avoid triggering that bug, we should avoid calling
+  // deflate() with Z_SYNC_FLUSH if the current bit position is 5.
+  // If it's 5, we insert an empty block consisting of 10 bits so
+  // that the bit position is 7 in the next byte.
+  //
+  // https://github.com/ianlancetaylor/libbacktrace/pull/87
+  int nbits;
+  deflatePending(&strm, Z_NULL, &nbits);
+  if (nbits == 5)
+    CHECK(deflatePrime(&strm, 10, 2));
+  CHECK(deflate(&strm, Z_SYNC_FLUSH));
+
+  assert(strm.avail_out > 0);
+  buf.resize(buf.size() - strm.avail_out);
+  buf.shrink_to_fit();
+  deflateEnd(&strm);
+  return buf;
+}
+
+ZlibCompressor::ZlibCompressor(u8 *buf, i64 size) {
+  std::string_view input{(char *)buf, (size_t)size};
+  std::vector<std::string_view> inputs = split(input);
+  std::vector<u64> adlers(inputs.size());
+  shards.resize(inputs.size());
+
+  // Compress each shard
+  tbb::parallel_for((i64)0, (i64)inputs.size(), [&](i64 i) {
+    adlers[i] = adler32(1, (u8 *)inputs[i].data(), inputs[i].size());
+    shards[i] = zlib_compress(inputs[i]);
+  });
+
+  // Combine checksums
+  checksum = adlers[0];
+  for (i64 i = 1; i < inputs.size(); i++)
+    checksum = adler32_combine(checksum, adlers[i], inputs[i].size());
+
+  // Comput the total size
+  compressed_size = 8; // the header and the trailer
+  for (std::vector<u8> &shard : shards)
+    compressed_size += shard.size();
+}
+
+void ZlibCompressor::write_to(u8 *buf) {
+  // Write a zlib-format header
+  buf[0] = 0x78;
+  buf[1] = 0x9c;
+
+  // Copy compressed data
+  std::vector<i64> offsets(shards.size());
+  offsets[0] = 2; // +2 for header
+  for (i64 i = 1; i < shards.size(); i++)
+    offsets[i] = offsets[i - 1] + shards[i - 1].size();
+
+  tbb::parallel_for((i64)0, (i64)shards.size(), [&](i64 i) {
+    memcpy(buf + offsets[i], shards[i].data(), shards[i].size());
+  });
+
+  // Write a trailer
+  u8 *end = buf + compressed_size;
+  end[-6] = 3;
+  end[-5] = 0;
+
+  // Write a checksum
+  *(ub32 *)(end - 4) = checksum;
+}
+
+static std::vector<u8> zstd_compress(std::string_view input) {
+  std::vector<u8> buf(ZSTD_COMPRESSBOUND(input.size()));
+  constexpr int LEVEL = 3; // compression level; must be between 1 to 22
+
+  size_t sz = ZSTD_compress(buf.data(), buf.size(), input.data(), input.size(),
+                            LEVEL);
+  assert(!ZSTD_isError(sz));
+  buf.resize(sz);
+  buf.shrink_to_fit();
+  return buf;
+}
+
+ZstdCompressor::ZstdCompressor(u8 *buf, i64 size) {
+  std::string_view input{(char *)buf, (size_t)size};
+  std::vector<std::string_view> inputs = split(input);
+  shards.resize(inputs.size());
+
+  // Compress each shard
+  tbb::parallel_for((i64)0, (i64)inputs.size(), [&](i64 i) {
+    shards[i] = zstd_compress(inputs[i]);
+  });
+
+  compressed_size = 0;
+  for (std::vector<u8> &shard : shards)
+    compressed_size += shard.size();
+}
+
+void ZstdCompressor::write_to(u8 *buf) {
+  // Copy compressed data
+  std::vector<i64> offsets(shards.size());
+  for (i64 i = 1; i < shards.size(); i++)
+    offsets[i] = offsets[i - 1] + shards[i - 1].size();
+
+  tbb::parallel_for((i64)0, (i64)shards.size(), [&](i64 i) {
+    memcpy(buf + offsets[i], shards[i].data(), shards[i].size());
+  });
+}
+
+} // namespace mold

lib/config.h.in

@@ -0,0 +1,7 @@
+#define MOLD_VERSION "@mold_VERSION@"
+#define MOLD_LIBDIR "@CMAKE_INSTALL_FULL_LIBDIR@"
+
+#cmakedefine HAVE_MADVISE 1
+#cmakedefine HAVE_UNAME 1
+#cmakedefine MOLD_USE_MIMALLOC 1
+#cmakedefine MOLD_USE_SYSTEM_MIMALLOC 1

lib/crc32.cc

@@ -0,0 +1,60 @@
+#include "common.h"
+
+#include <tbb/parallel_for_each.h>
+#include <zlib.h>
+
+namespace mold {
+
+// This function "forges" a CRC. That is, given the current and a desired
+// CRC32 value, crc32_solve() returns a binary blob to add to the end of
+// the original data to yield the desired CRC. Trailing garbage is ignored
+// by many bianry file formats, so you can create a file with a desired
+// CRC using crc32_solve(). We need it for --separate-debug-file.
+std::vector<u8> crc32_solve(u32 current, u32 desired) {
+  constexpr u32 poly = 0xedb88320;
+  u32 x = ~desired;
+
+  // Each iteration computes x = (x * x^-1) mod poly.
+  for (i64 i = 0; i < 32; i++) {
+    x = std::rotl(x, 1);
+    x ^= (x & 1) * (poly << 1);
+  }
+
+  x ^= ~current;
+
+  std::vector<u8> out(4);
+  out[0] = x;
+  out[1] = x >> 8;
+  out[2] = x >> 16;
+  out[3] = x >> 24;
+  return out;
+}
+
+// Compute a CRC for given data in parallel
+u32 compute_crc32(u32 crc, u8 *buf, i64 len) {
+  struct Shard {
+    u8 *buf;
+    i64 len;
+    u32 crc;
+  };
+
+  constexpr i64 shard_size = 1024 * 1024; // 1 MiB
+  std::vector<Shard> shards;
+
+  while (len > 0) {
+    i64 sz = std::min(len, shard_size);
+    shards.push_back({buf, sz, 0});
+    buf += sz;
+    len -= sz;
+  }
+
+  tbb::parallel_for_each(shards, [](Shard &shard) {
+    shard.crc = crc32(0, shard.buf, shard.len);
+  });
+
+  for (Shard &shard : shards)
+    crc = crc32_combine(crc, shard.crc, shard.len);
+  return crc;
+}
+
+} // namespace mold

lib/demangle.cc

@@ -0,0 +1,42 @@
+#include "common.h"
+
+#include <cstdlib>
+
+#ifndef _WIN32
+#include <cxxabi.h>
+#endif
+
+#include "../third-party/rust-demangle/rust-demangle.h"
+
+namespace mold {
+
+std::optional<std::string_view> demangle_cpp(std::string_view name) {
+  static thread_local char *buf;
+  static thread_local size_t buflen;
+
+  // TODO(cwasser): Actually demangle Symbols on Windows using e.g.
+  // `UnDecorateSymbolName` from Dbghelp, maybe even Itanium symbols?
+#ifndef _WIN32
+  if (name.starts_with("_Z")) {
+    int status;
+    char *p = abi::__cxa_demangle(std::string(name).c_str(), buf, &buflen, &status);
+    if (status == 0) {
+      buf = p;
+      return p;
+    }
+  }
+#endif
+
+  return {};
+}
+
+std::optional<std::string_view> demangle_rust(std::string_view name) {
+  static thread_local char *buf;
+  free(buf);
+  buf = rust_demangle(std::string(name).c_str(), 0);
+  if (buf)
+    return buf;
+  return {};
+}
+
+} // namespace mold

lib/filepath.cc

@@ -0,0 +1,42 @@
+#include "common.h"
+
+#include <filesystem>
+#include <sys/stat.h>
+
+#ifdef __APPLE__
+# include <mach-o/dyld.h>
+#endif
+
+#ifdef __FreeBSD__
+# include <sys/sysctl.h>
+#endif
+
+namespace mold {
+
+// Returns the path of the mold executable itself
+std::string get_self_path() {
+#if __APPLE__ || _WIN32
+  fprintf(stderr, "mold: get_self_path is not supported");
+  exit(1);
+#elif __FreeBSD__
+  // /proc may not be mounted on FreeBSD. The proper way to get the
+  // current executable's path is to use sysctl(2).
+  int mib[4];
+  mib[0] = CTL_KERN;
+  mib[1] = KERN_PROC;
+  mib[2] = KERN_PROC_PATHNAME;
+  mib[3] = -1;
+
+  size_t size;
+  sysctl(mib, 4, NULL, &size, NULL, 0);
+
+  std::string path;
+  path.resize(size);
+  sysctl(mib, 4, path.data(), &size, NULL, 0);
+  return path;
+#else
+  return std::filesystem::read_symlink("/proc/self/exe").string();
+#endif
+}
+
+} // namespace mold

lib/gentoo-test.sh

@@ -0,0 +1,69 @@
+#!/bin/bash
+#
+# This test script takes a Gentoo package name and tries to build it
+# using mold in a Podman environment. We chose Gentoo Linux as a test
+# target, because its source-based package allows us to build programs
+# locally and run their test suites without any hassle.
+#
+# You can get a complete list of Gentoo packages availalbe for testing
+# with the following command:
+#
+# podman run --rm mold-gentoo emerge --color n -s '' | \
+#   perl -ne 'next unless m!^\*\s+(\S+/\S+)!; print "$1\n"'
+
+package="$1"
+
+if [ "$package" = "" ]; then
+  echo "Usage: $0 gentoo-package-name"
+  exit 1
+fi
+
+set -x
+
+# Create a Podman image
+if ! podman image ls mold-gentoo | grep -q mold-gentoo; then
+  set -e
+  cat <<EOF | podman build -t mold-gentoo -
+FROM docker.io/gentoo/stage3
+RUN emerge-webrsync
+RUN echo 'USE="X ssl elogind -systemd corefonts truetype jpeg jpeg2k tiff zstd static-libs binary -perl"' >> /etc/portage/make.conf && \
+    echo 'ACCEPT_KEYWORDS="~amd64"' >> /etc/portage/make.conf && \
+    echo 'ACCEPT_LICENSE="* -@EULA"' >> /etc/portage/make.conf && \
+    echo 'FEATURES="\${FEATURE} noclean nostrip ccache -ipc-sandbox -network-sandbox -pid-sandbox -sandbox"' >> /etc/portage/make.conf && \
+    echo 'CCACHE_DIR="/ccache"' >> /etc/portage/make.conf && \
+    FEATURES='getbinpkg binpkg-request-signature' emerge gdb lld llvm-core/clang vim emacs strace ccache xeyes dev-build/cmake dev-vcs/git && \
+    rm -rf /var/tmp/portage
+EOF
+  set +e
+fi
+
+git_hash=$(./dist/mold --version | perl -ne '/\((\w+)/; print $1;')
+
+if [ "$package" = dev-libs/concurrencykit ]; then
+  echo "Skipping known broken package: $package"
+  exit 0
+fi
+
+# Build a given package in Podman
+cmd1='(cd /usr/bin; ln -sf /mold/dist/mold $(realpath ld))'
+cmd2="MAKEOPTS=-'j$(nproc) --load-average=100' emerge --onlydeps $package"
+cmd3="MAKEOPTS='-j$(nproc) --load-average=100' FEATURES=test emerge $package"
+filename=`echo "$package" | sed 's!/!_!g'`
+podman="podman run --rm --pids-limit=-1 --cap-add=SYS_PTRACE -v `pwd`:/mold:ro -v /var/cache/ccache-gentoo:/ccache mold-gentoo timeout -v -k 15s 3h"
+dir=gentoo/$git_hash
+
+mkdir -p "$dir"/success "$dir"/failure
+
+$podman nice -n 19 bash -c "$cmd1 && $cmd2 && $cmd3" >& "$dir"/"$filename".mold
+if [ $? = 0 ]; then
+  mv "$dir"/"$filename".mold "$dir"/success
+else
+  mv "$dir"/"$filename".mold "$dir"/failure
+fi
+
+$podman nice -n 19 bash -c "$cmd2 && $cmd3" >& "$dir"/"$filename".ld
+if [ $? = 0 ]; then
+  mv "$dir"/"$filename".ld "$dir"/success
+else
+  mv "$dir"/"$filename".ld "$dir"/failure
+fi

lib/glob.cc

@@ -0,0 +1,156 @@
+#include "common.h"
+
+#include <cstring>
+
+namespace mold {
+
+std::optional<Glob> Glob::compile(std::string_view pat) {
+  std::vector<Element> vec;
+
+  while (!pat.empty()) {
+    u8 c = pat[0];
+    pat = pat.substr(1);
+
+    switch (c) {
+    case '[': {
+      // Here are a few bracket pattern examples:
+      //
+      // [abc]: a, b or c
+      // [$\]!]: $, ] or !
+      // [a-czg-i]: a, b, c, z, g, h, or i
+      // [^a-z]: Any character except lowercase letters
+      vec.emplace_back(BRACKET);
+      std::bitset<256> &bitset = vec.back().bitset;
+
+      bool negate = false;
+      if (!pat.empty() && pat[0] == '^') {
+        negate = true;
+        pat = pat.substr(1);
+      }
+
+      bool closed = false;
+
+      while (!pat.empty()) {
+        if (pat[0] == ']') {
+          pat = pat.substr(1);
+          closed = true;
+          break;
+        }
+
+        if (pat[0] == '\\') {
+          pat = pat.substr(1);
+          if (pat.empty())
+            return {};
+        }
+
+        if (pat.size() >= 3 && pat[1] == '-') {
+          u8 start = pat[0];
+          u8 end = pat[2];
+          pat = pat.substr(3);
+
+          if (end == '\\') {
+            if (pat.empty())
+              return {};
+            end = pat[0];
+            pat = pat.substr(1);
+          }
+
+          if (end < start)
+            return {};
+
+          for (i64 i = start; i <= end; i++)
+            bitset[i] = true;
+        } else {
+          bitset[(u8)pat[0]] = true;
+          pat = pat.substr(1);
+        }
+      }
+
+      if (!closed)
+        return {};
+
+      if (negate)
+        bitset.flip();
+      break;
+    }
+    case '?':
+      vec.emplace_back(QUESTION);
+      break;
+    case '*':
+      vec.emplace_back(STAR);
+      break;
+    case '\\':
+      if (pat.empty())
+        return {};
+      if (vec.empty() || vec.back().kind != STRING)
+        vec.emplace_back(STRING);
+      vec.back().str += pat[0];
+      pat = pat.substr(1);
+      break;
+    default:
+      if (vec.empty() || vec.back().kind != STRING)
+        vec.emplace_back(STRING);
+      vec.back().str += c;
+      break;
+    }
+  }
+
+  return {Glob{std::move(vec)}};
+}
+
+bool Glob::match(std::string_view str) {
+  return do_match(str, elements);
+}
+
+bool Glob::do_match(std::string_view str, std::span<Element> elements) {
+  while (!elements.empty()) {
+    Element &e = elements[0];
+    elements = elements.subspan(1);
+
+    switch (e.kind) {
+    case STRING:
+      if (!str.starts_with(e.str))
+        return false;
+      str = str.substr(e.str.size());
+      break;
+    case STAR:
+      if (elements.empty())
+        return true;
+
+      // Patterns like "*foo*bar*" should be much more common than more
+      // complex ones like "*foo*[abc]*" or "*foo**?bar*", so we optimize
+      // the former case here.
+      if (elements[0].kind == STRING) {
+        for (;;) {
+          size_t pos = str.find(elements[0].str);
+          if (pos == str.npos)
+            return false;
+          if (do_match(str.substr(pos + elements[0].str.size()),
+                       elements.subspan(1)))
+            return true;
+          str = str.substr(pos + 1);
+        }
+      }
+
+      // Other cases are handled here.
+      for (i64 j = 0; j < str.size(); j++)
+        if (do_match(str.substr(j), elements))
+          return true;
+      return false;
+    case QUESTION:
+      if (str.empty())
+        return false;
+      str = str.substr(1);
+      break;
+    case BRACKET:
+      if (str.empty() || !e.bitset[str[0]])
+        return false;
+      str = str.substr(1);
+      break;
+    }
+  }
+
+  return str.empty();
+}
+
+} // namespace mold

lib/hyperloglog.cc

@@ -0,0 +1,20 @@
+// This file implements HyperLogLog algorithm, which estimates
+// the number of unique items in a given multiset.
+//
+// For more info, read
+// https://engineering.fb.com/2018/12/13/data-infrastructure/hyperloglog
+
+#include "common.h"
+
+#include <cmath>
+
+namespace mold {
+
+i64 HyperLogLog::get_cardinality() const {
+  double z = 0;
+  for (i64 val : buckets)
+    z += std::ldexp(1.0, -val);
+  return ALPHA * NBUCKETS * NBUCKETS / z;
+}
+
+} // namespace mold

lib/integers.h

@@ -0,0 +1,144 @@
+// This file defines integral types for file input/output. We need to use
+// these types instead of the plain integers (such as uint32_t or int32_t)
+// when reading from/writing to an mmap'ed file area for the following
+// reasons:
+//
+// 1. mold is always a cross linker and should not depend on what host it
+//    is running on. For example, users should be able to run mold on a
+//    big-endian SPARC machine to create a little-endian RV64 binary.
+//
+// 2. Even though data members in all ELF data strucutres are naturally
+//    aligned, they are not guaranteed to be aligned on memory because of
+//    archive files. Archive files (.a files) align each member only to a
+//    2 byte boundary, so anything larger than 2 bytes may be misaligned
+//    in an mmap'ed memory. Misaligned access is an undefined behavior in
+//    C/C++, so we shouldn't cast an arbitrary pointer to a uint32_t, for
+//    example, to read a 32 bit value.
+//
+// The data types defined in this file don't depend on host byte order and
+// don't do unaligned access. Note that modern compilers are smart enough
+// to recognize shift and bitwise OR patterns and compile them into a
+// single load instruction.
+
+#pragma once
+
+#include <cstdint>
+
+#if !defined(__LITTLE_ENDIAN__) && !defined(__BIG_ENDIAN__)
+# if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#  define __LITTLE_ENDIAN__ 1
+# elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+#  define __BIG_ENDIAN__ 1
+# else
+#  error "unknown host byte order"
+# endif
+#endif
+
+namespace mold {
+
+typedef uint8_t u8;
+typedef uint16_t u16;
+typedef uint32_t u32;
+typedef uint64_t u64;
+
+typedef int8_t i8;
+typedef int16_t i16;
+typedef int32_t i32;
+typedef int64_t i64;
+
+template <typename T, bool is_le, int size = sizeof(T)>
+class Integer {
+public:
+  constexpr Integer() = default;
+
+  constexpr Integer(T x) requires (is_le && size == 2)
+    : buf{(u8)x, (u8)(x >> 8)} {}
+
+  constexpr Integer(T x) requires (is_le && size == 3)
+    : buf{(u8)x, (u8)(x >> 8), (u8)(x >> 16)} {}
+
+  constexpr Integer(T x) requires (is_le && size == 4)
+    : buf{(u8)x, (u8)(x >> 8), (u8)(x >> 16), (u8)(x >> 24)} {}
+
+  constexpr Integer(T x) requires (is_le && size == 8)
+    : buf{(u8)x,         (u8)(x >> 8),  (u8)(x >> 16), (u8)(x >> 24),
+          (u8)(x >> 32), (u8)(x >> 40), (u8)(x >> 48), (u8)(x >> 56)} {}
+
+  constexpr Integer(T x) requires (!is_le && size == 2)
+    : buf{(u8)(x >> 8), (u8)x} {}
+
+  constexpr Integer(T x) requires (!is_le && size == 3)
+    : buf{(u8)(x >> 16), (u8)(x >> 8), (u8)x} {}
+
+  constexpr Integer(T x) requires (!is_le && size == 4)
+    : buf{(u8)(x >> 24), (u8)(x >> 16), (u8)(x >> 8), (u8)x} {}
+
+  constexpr Integer(T x) requires (!is_le && size == 8)
+    : buf{(u8)(x >> 56), (u8)(x >> 48), (u8)(x >> 40), (u8)(x >> 32),
+          (u8)(x >> 24), (u8)(x >> 16), (u8)(x >> 8),  (u8)x} {}
+
+  operator T() const {
+    if constexpr (is_le) {
+      if constexpr (size == 2)
+        return buf[1] << 8 | buf[0];
+      else if constexpr (size == 3)
+        return buf[2] << 16 | buf[1] << 8 | buf[0];
+      else if constexpr (size == 4)
+        return buf[3] << 24 | buf[2] << 16 | buf[1] << 8 | buf[0];
+      else
+        return (u64)buf[7] << 56 | (u64)buf[6] << 48 |
+               (u64)buf[5] << 40 | (u64)buf[4] << 32 |
+               (u64)buf[3] << 24 | (u64)buf[2] << 16 |
+               (u64)buf[1] << 8  | (u64)buf[0];
+    } else {
+      if constexpr (size == 2)
+        return buf[0] << 8 | buf[1];
+      else if constexpr (size == 3)
+        return buf[0] << 16 | buf[1] << 8 | buf[2];
+      else if constexpr (size == 4)
+        return buf[0] << 24 | buf[1] << 16 | buf[2] << 8 | buf[3];
+      else
+        return (u64)buf[0] << 56 | (u64)buf[1] << 48 |
+               (u64)buf[2] << 40 | (u64)buf[3] << 32 |
+               (u64)buf[4] << 24 | (u64)buf[5] << 16 |
+               (u64)buf[6] << 8  | (u64)buf[7];
+    }
+  }
+
+  Integer &operator=(T x) {
+    new (this) Integer(x);
+    return *this;
+  }
+
+  Integer &operator++()    { return *this = *this + 1; }
+  Integer operator++(int)  { return ++*this - 1; }
+  Integer &operator--()    { return *this = *this - 1; }
+  Integer operator--(int)  { return --*this + 1; }
+  Integer &operator+=(T x) { return *this = *this + x; }
+  Integer &operator-=(T x) { return *this = *this - x; }
+  Integer &operator&=(T x) { return *this = *this & x; }
+  Integer &operator|=(T x) { return *this = *this | x; }
+
+private:
+  u8 buf[size];
+};
+
+using il16 = Integer<i16, true>;
+using il32 = Integer<i32, true>;
+using il64 = Integer<i64, true>;
+
+using ul16 = Integer<u16, true>;
+using ul24 = Integer<u32, true, 3>;
+using ul32 = Integer<u32, true>;
+using ul64 = Integer<u64, true>;
+
+using ib16 = Integer<i16, false>;
+using ib32 = Integer<i32, false>;
+using ib64 = Integer<i64, false>;
+
+using ub16 = Integer<u16, false>;
+using ub24 = Integer<u32, false, 3>;
+using ub32 = Integer<u32, false>;
+using ub64 = Integer<u64, false>;
+
+} // namespace mold

lib/jobs-unix.cc

@@ -0,0 +1,50 @@
+// Many build systems attempt to invoke as many linker processes as there
+// are cores, based on the assumption that the linker is single-threaded.
+// However, since mold is multi-threaded, such build systems' behavior is
+// not beneficial and just increases the overall peak memory usage.
+// On machines with limited memory, this could lead to an out-of-memory
+// error.
+//
+// This file implements a feature that limits the number of concurrent
+// mold processes to just 1 for each user. It is intended to be used as
+// `MOLD_JOBS=1 ninja` or `MOLD_JOBS=1 make -j$(nproc)`.
+
+#include "common.h"
+
+#include <cstdlib>
+#include <fcntl.h>
+#include <pwd.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+namespace mold {
+
+static int lock_fd = -1;
+
+void acquire_global_lock() {
+  char *jobs = getenv("MOLD_JOBS");
+  if (!jobs || jobs != "1"s)
+    return;
+
+  std::string path;
+  if (char *dir = getenv("XDG_RUNTIME_DIR"))
+    path = dir + "/mold-lock"s;
+  else
+    path = "/tmp/mold-lock-"s + getpwuid(getuid())->pw_name;
+
+  int fd = open(path.c_str(), O_WRONLY | O_CREAT | O_CLOEXEC, 0600);
+  if (fd == -1)
+    return;
+
+  if (lockf(fd, F_LOCK, 0) == -1)
+    return;
+  lock_fd = fd;
+}
+
+void release_global_lock() {
+  if (lock_fd != -1)
+    close(lock_fd);
+}
+
+} // namespace mold

lib/jobs-win32.cc

@@ -0,0 +1,6 @@
+namespace mold {
+
+void acquire_global_lock() {}
+void release_global_lock() {}
+
+} // namespace mold

lib/mapped-file-unix.cc

@@ -0,0 +1,51 @@
+#include "common.h"
+
+namespace mold {
+
+MappedFile *open_file_impl(const std::string &path, std::string &error) {
+  i64 fd = ::open(path.c_str(), O_RDONLY);
+  if (fd == -1) {
+    if (errno != ENOENT)
+      error = "opening " + path + " failed: " + errno_string();
+    return nullptr;
+  }
+
+  struct stat st;
+  if (fstat(fd, &st) == -1)
+    error = path + ": fstat failed: " + errno_string();
+
+  MappedFile *mf = new MappedFile;
+  mf->name = path;
+  mf->size = st.st_size;
+
+  if (st.st_size > 0) {
+    mf->data = (u8 *)mmap(nullptr, st.st_size, PROT_READ | PROT_WRITE,
+                          MAP_PRIVATE, fd, 0);
+    if (mf->data == MAP_FAILED)
+      error = path + ": mmap failed: " + errno_string();
+  }
+
+  close(fd);
+  return mf;
+}
+
+void MappedFile::unmap() {
+  if (size == 0 || parent || !data)
+    return;
+  munmap(data, size);
+  data = nullptr;
+}
+
+void MappedFile::close_fd() {
+  if (fd == -1)
+    return;
+  close(fd);
+  fd = -1;
+}
+
+void MappedFile::reopen_fd(const std::string &path) {
+  if (fd == -1)
+    fd = open(path.c_str(), O_RDONLY);
+}
+
+} // namespace mold

lib/mapped-file-win32.cc

@@ -0,0 +1,81 @@
+#include "common.h"
+
+namespace mold {
+
+MappedFile *open_file_impl(const std::string &path, std::string &error) {
+  HANDLE fd = CreateFileA(path.c_str(), GENERIC_READ,
+                          FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
+                          nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
+
+  if (fd == INVALID_HANDLE_VALUE) {
+    auto err = GetLastError();
+    if (err != ERROR_FILE_NOT_FOUND)
+      error = "opening " + path + " failed: " + errno_string();
+    return nullptr;
+  }
+
+  if (GetFileType(fd) != FILE_TYPE_DISK) {
+    CloseHandle(fd);
+    return nullptr;
+  }
+
+  DWORD size_hi;
+  DWORD size_lo = GetFileSize(fd, &size_hi);
+
+  if (size_lo == INVALID_FILE_SIZE) {
+    error = path + ": GetFileSize failed: " + errno_string();
+    return nullptr;
+  }
+
+  u64 size = ((u64)size_hi << 32) + size_lo;
+
+  MappedFile *mf = new MappedFile;
+  mf->name = path;
+  mf->size = size;
+  mf->fd = fd;
+
+  if (size > 0) {
+    HANDLE h = CreateFileMapping(fd, nullptr, PAGE_READONLY, 0, size, nullptr);
+    if (!h) {
+      error = path + ": CreateFileMapping failed: " + errno_string();
+      return nullptr;
+    }
+
+    mf->data = (u8 *)MapViewOfFile(h, FILE_MAP_COPY, 0, 0, size);
+    CloseHandle(h);
+
+    if (!mf->data) {
+      error = path + ": MapViewOfFile failed: " + errno_string();
+      return nullptr;
+    }
+  }
+
+  return mf;
+}
+
+void MappedFile::unmap() {
+  if (size == 0 || parent || !data)
+    return;
+
+  UnmapViewOfFile(data);
+  if (fd != INVALID_HANDLE_VALUE)
+    CloseHandle(fd);
+
+  data = nullptr;
+}
+
+void MappedFile::close_fd() {
+  if (fd == INVALID_HANDLE_VALUE)
+    return;
+  CloseHandle(fd);
+  fd = INVALID_HANDLE_VALUE;
+}
+
+void MappedFile::reopen_fd(const std::string &path) {
+  if (fd == INVALID_HANDLE_VALUE)
+    fd = CreateFileA(path.c_str(), GENERIC_READ,
+                     FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
+                     nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
+}
+
+} // namespace mold

lib/mimalloc.cc

@@ -0,0 +1,24 @@
+#include "common.h"
+
+// Including mimalloc-new-delete.h overrides new/delete operators.
+// We need it only when we are using mimalloc as a dynamic library.
+#if MOLD_USE_SYSTEM_MIMALLOC
+# include <mimalloc-new-delete.h>
+#endif
+
+// Silence mimalloc warning messages that users can just ignore.
+#if MOLD_USE_MIMALLOC
+# include <mimalloc.h>
+
+namespace mold {
+void set_mimalloc_options() {
+  mi_option_disable(mi_option_verbose);
+  mi_option_disable(mi_option_show_errors);
+}
+}
+
+#else
+namespace mold {
+void set_mimalloc_options() {}
+}
+#endif

lib/multi-glob.cc

@@ -0,0 +1,186 @@
+// This file implements the Aho-Corasick algorithm to match multiple
+// glob patterns to symbol strings as quickly as possible.
+//
+// Here are some examples of glob patterns:
+//
+//    qt_private_api_tag*
+//    *16QAccessibleCache*
+//    *32QAbstractFileIconProviderPrivate*
+//    *17QPixmapIconEngine*
+//
+// `*` is a wildcard that matches any substring. We sometimes have
+// hundreds of glob patterns and have to match them against millions
+// of symbol strings.
+//
+// Aho-Corasick cannot handle complex patterns such as `*foo*bar*`.
+// We handle such patterns with the Glob class. Glob is relatively
+// slow, but complex patterns are rare in practice, so it should be
+// OK.
+
+#include "common.h"
+
+#include <queue>
+#include <regex>
+
+namespace mold {
+
+std::optional<i64> MultiGlob::find(std::string_view str) {
+  std::call_once(once, [&] { compile(); });
+  i64 val = -1;
+
+  // Match against simple glob patterns
+  if (root)
+    val = find_aho_corasick(str);
+
+  // Match against complex glob patterns
+  for (std::pair<Glob, i64> &glob : globs)
+    if (glob.first.match(str))
+      val = std::max(val, glob.second);
+
+  if (val == -1)
+    return {};
+  return val;
+}
+
+i64 MultiGlob::find_aho_corasick(std::string_view str) {
+  TrieNode *node = root.get();
+  i64 val = -1;
+
+  auto walk = [&](u8 c) {
+    for (;;) {
+      if (node->children[c]) {
+        node = node->children[c].get();
+        val = std::max(val, node->value);
+        return;
+      }
+
+      if (!node->suffix_link)
+        return;
+      node = node->suffix_link;
+    }
+  };
+
+  walk('\0');
+
+  for (u8 c : str) {
+    if (prefix_match && node == root.get())
+      return val;
+    walk(c);
+  }
+
+  walk('\0');
+  return val;
+}
+
+static bool is_simple_pattern(std::string_view pat) {
+  static std::regex re(R"(\*?[^*[?]+\*?)", std::regex_constants::optimize);
+  return std::regex_match(pat.begin(), pat.end(), re);
+}
+
+static std::string handle_stars(std::string_view pat) {
+  std::string str(pat);
+
+  // Convert "foo" -> "\0foo\0", "*foo" -> "foo\0", "foo*" -> "\0foo"
+  // and "*foo*" -> "foo". Aho-Corasick can do only substring matching,
+  // so we use \0 as beginning/end-of-string markers.
+  if (str.starts_with('*') && str.ends_with('*'))
+    return str.substr(1, str.size() - 2);
+  if (str.starts_with('*'))
+    return str.substr(1) + "\0"s;
+  if (str.ends_with('*'))
+    return "\0"s + str.substr(0, str.size() - 1);
+  return "\0"s + str + "\0"s;
+}
+
+bool MultiGlob::add(std::string_view pat, i64 val) {
+  assert(!is_compiled);
+  assert(!pat.empty());
+
+  strings.emplace_back(pat);
+
+  // Complex glob pattern
+  if (!is_simple_pattern(pat)) {
+    if (std::optional<Glob> glob = Glob::compile(pat)) {
+      globs.emplace_back(std::move(*glob), val);
+      return true;
+    }
+    return false;
+  }
+
+  // Simple glob pattern
+  if (!root)
+    root.reset(new TrieNode);
+  TrieNode *node = root.get();
+
+  for (u8 c : handle_stars(pat)) {
+    if (!node->children[c])
+      node->children[c].reset(new TrieNode);
+    node = node->children[c].get();
+  }
+
+  node->value = std::max(node->value, val);
+  return true;
+}
+
+void MultiGlob::compile() {
+  is_compiled = true;
+  if (root) {
+    fix_suffix_links(*root);
+    fix_values();
+
+    // If no pattern starts with '*', set prefix_match to true.
+    // We'll use this flag for optimization.
+    prefix_match = true;
+    for (i64 i = 1; i < 256; i++) {
+      if (root->children[i]) {
+        prefix_match = false;
+        break;
+      }
+    }
+  }
+}
+
+void MultiGlob::fix_suffix_links(TrieNode &node) {
+  for (i64 i = 0; i < 256; i++) {
+    if (!node.children[i])
+      continue;
+
+    TrieNode &child = *node.children[i];
+
+    TrieNode *cur = node.suffix_link;
+    for (;;) {
+      if (!cur) {
+        child.suffix_link = root.get();
+        break;
+      }
+
+      if (cur->children[i]) {
+        child.suffix_link = cur->children[i].get();
+        break;
+      }
+
+      cur = cur->suffix_link;
+    }
+
+    fix_suffix_links(child);
+  }
+}
+
+void MultiGlob::fix_values() {
+  std::queue<TrieNode *> queue;
+  queue.push(root.get());
+
+  do {
+    TrieNode *node = queue.front();
+    queue.pop();
+
+    for (std::unique_ptr<TrieNode> &child : node->children) {
+      if (!child)
+        continue;
+      child->value = std::max(child->value, child->suffix_link->value);
+      queue.push(child.get());
+    }
+  } while (!queue.empty());
+}
+
+} // namespace mold

lib/perf.cc

@@ -0,0 +1,116 @@
+#include "common.h"
+
+#include <functional>
+#include <iomanip>
+#include <ios>
+#include <tbb/concurrent_vector.h>
+
+#ifndef _WIN32
+#include <sys/resource.h>
+#include <sys/time.h>
+#endif
+
+namespace mold {
+
+i64 Counter::get_value() {
+  return values.combine(std::plus());
+}
+
+void Counter::print() {
+  ranges::stable_sort(instances, {}, [](Counter *x) { return x->get_value(); });
+
+  for (Counter *c : instances)
+    std::cout << std::setw(20) << std::right << c->name
+              << "=" << c->get_value() << "\n";
+}
+
+static i64 now_nsec() {
+  return (i64)std::chrono::steady_clock::now().time_since_epoch().count();
+}
+
+static std::pair<i64, i64> get_usage() {
+#ifdef _WIN32
+  auto to_nsec = [](FILETIME t) -> i64 {
+    return (((u64)t.dwHighDateTime << 32) + (u64)t.dwLowDateTime) * 100;
+  };
+
+  FILETIME creation, exit, kernel, user;
+  GetProcessTimes(GetCurrentProcess(), &creation, &exit, &kernel, &user);
+  return {to_nsec(user), to_nsec(kernel)};
+#else
+  auto to_nsec = [](struct timeval t) -> i64 {
+    return (i64)t.tv_sec * 1'000'000'000 + t.tv_usec * 1'000;
+  };
+
+  struct rusage ru;
+  getrusage(RUSAGE_SELF, &ru);
+  return {to_nsec(ru.ru_utime), to_nsec(ru.ru_stime)};
+#endif
+}
+
+TimerRecord::TimerRecord(std::string name, TimerRecord *parent)
+  : name(name), parent(parent) {
+  start = now_nsec();
+  std::tie(user, sys) = get_usage();
+  if (parent)
+    parent->children.push_back(this);
+}
+
+void TimerRecord::stop() {
+  if (stopped)
+    return;
+  stopped = true;
+
+  i64 user2;
+  i64 sys2;
+  std::tie(user2, sys2) = get_usage();
+
+  end = now_nsec();
+  user = user2 - user;
+  sys = sys2 - sys;
+}
+
+static void print_rec(TimerRecord &rec, i64 indent) {
+  printf(" % 8.3f % 8.3f % 8.3f  %s%s\n",
+         ((double)rec.user / 1'000'000'000),
+         ((double)rec.sys / 1'000'000'000),
+         (((double)rec.end - rec.start) / 1'000'000'000),
+         std::string(indent * 2, ' ').c_str(),
+         rec.name.c_str());
+
+  ranges::stable_sort(rec.children, {}, &TimerRecord::start);
+
+  for (TimerRecord *child : rec.children)
+    print_rec(*child, indent + 1);
+}
+
+void print_timer_records(
+    tbb::concurrent_vector<std::unique_ptr<TimerRecord>> &records) {
+  for (i64 i = records.size() - 1; i >= 0; i--)
+    records[i]->stop();
+
+  for (i64 i = 0; i < records.size(); i++) {
+    TimerRecord &inner = *records[i];
+    if (inner.parent)
+      continue;
+
+    for (i64 j = i - 1; j >= 0; j--) {
+      TimerRecord &outer = *records[j];
+      if (outer.start <= inner.start && inner.end <= outer.end) {
+        inner.parent = &outer;
+        outer.children.push_back(&inner);
+        break;
+      }
+    }
+  }
+
+  std::cout << "     User   System     Real  Name\n";
+
+  for (std::unique_ptr<TimerRecord> &rec : records)
+    if (!rec->parent)
+      print_rec(*rec, 0);
+
+  std::cout << std::flush;
+}
+
+} // namespace mold

lib/random.cc

@@ -0,0 +1,20 @@
+#include "common.h"
+
+#include <random>
+
+namespace mold {
+
+void get_random_bytes(u8 *buf, i64 size) {
+  std::random_device rand;
+  i64 i = 0;
+
+  for (; i < size - 4; i += 4) {
+    u32 val = rand();
+    memcpy(buf + i, &val, 4);
+  }
+
+  u32 val = rand();
+  memcpy(buf + i, &val, size - i);
+}
+
+} // namespace mold

lib/signal-unix.cc

@@ -0,0 +1,88 @@
+#include "common.h"
+
+#include <csignal>
+#include <tbb/version.h>
+
+#ifdef __FreeBSD__
+# include <sys/sysctl.h>
+# include <unistd.h>
+#endif
+
+namespace mold {
+
+std::string errno_string() {
+  // strerror is not thread-safe, so guard it with a lock.
+  static std::mutex mu;
+  std::scoped_lock lock(mu);
+  return strerror(errno);
+}
+
+void cleanup() {
+  if (output_tmpfile)
+    unlink(output_tmpfile);
+}
+
+// mold mmap's an output file, and the mmap succeeds even if there's
+// no enough space left on the filesystem. The actual disk blocks are
+// not allocated on the mmap call but when the program writes to it
+// for the first time.
+//
+// If a disk becomes full as a result of a write to an mmap'ed memory
+// region, the failure of the write is reported as a SIGBUS or structured
+// exeption with code EXCEPTION_IN_PAGE_ERROR on Windows. This
+// signal handler catches that signal and prints out a user-friendly
+// error message. Without this, it is very hard to realize that the
+// disk might be full.
+static std::string sigabrt_msg;
+
+static void sighandler(int signo, siginfo_t *info, void *ucontext) {
+  static std::mutex mu;
+  std::scoped_lock lock{mu};
+
+  // Handle disk full error
+  switch (signo) {
+  case SIGSEGV:
+  case SIGBUS:
+    if (output_buffer_start <= info->si_addr &&
+        info->si_addr < output_buffer_end) {
+      const char msg[] = "mold: failed to write to an output file. Disk full?\n";
+      (void)!write(STDERR_FILENO, msg, sizeof(msg) - 1);
+    }
+    break;
+  case SIGABRT: {
+    (void)!write(STDERR_FILENO, &sigabrt_msg[0], sigabrt_msg.size());
+    break;
+  }
+  }
+
+  // Re-throw the signal
+  signal(SIGSEGV, SIG_DFL);
+  signal(SIGBUS, SIG_DFL);
+  signal(SIGABRT, SIG_DFL);
+
+  cleanup();
+  raise(signo);
+}
+
+void install_signal_handler() {
+  struct sigaction action;
+  action.sa_sigaction = sighandler;
+  sigemptyset(&action.sa_mask);
+  action.sa_flags = SA_SIGINFO;
+
+  sigaction(SIGSEGV, &action, NULL);
+  sigaction(SIGBUS, &action, NULL);
+
+  // OneTBB 2021.9.0 has the interface version 12090.
+  if (TBB_runtime_interface_version() < 12090) {
+    sigabrt_msg = "mold: aborted\n"
+      "mold: mold with libtbb version 2021.9.0 or older is known to be unstable "
+      "under heavy load. Your libtbb version is " +
+      std::string(TBB_runtime_version()) +
+      ". Please upgrade your libtbb library and try again.\n";
+
+    sigaction(SIGABRT, &action, NULL);
+  }
+}
+
+} // namespace mold

lib/signal-win32.cc

@@ -0,0 +1,55 @@
+#include "common.h"
+
+#include <windows.h>
+
+namespace mold {
+
+void cleanup() {
+  if (output_tmpfile)
+    _unlink(output_tmpfile);
+}
+
+std::string errno_string() {
+  LPVOID buf;
+  DWORD dw = GetLastError();
+
+  FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
+                FORMAT_MESSAGE_FROM_SYSTEM |
+                FORMAT_MESSAGE_IGNORE_INSERTS,
+                nullptr, dw,
+                MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
+                (LPTSTR)&buf, 0, nullptr);
+
+  std::string ret = (char *)buf;
+  LocalFree(buf);
+  return ret;
+}
+
+static LONG WINAPI vectored_handler(_EXCEPTION_POINTERS *exception_info) {
+  static std::mutex mu;
+  std::scoped_lock lock{mu};
+
+  PEXCEPTION_RECORD rec = exception_info->ExceptionRecord;
+  ULONG_PTR *p = rec->ExceptionInformation;
+
+  if (rec->ExceptionCode == EXCEPTION_IN_PAGE_ERROR &&
+      (ULONG_PTR)output_buffer_start <= p[1] &&
+      p[1] < (ULONG_PTR)output_buffer_end) {
+    static const char msg[] =
+      "mold: failed to write to an output file. Disk full?\n";
+    (void)!_write(_fileno(stderr), msg, sizeof(msg) - 1);
+  } else if (rec->ExceptionCode == EXCEPTION_STACK_OVERFLOW) {
+    static const char msg[] =
+      "mold: stack overflow\n";
+    (void)!_write(_fileno(stderr), msg, sizeof(msg) - 1);
+  }
+
+  cleanup();
+  _exit(1);
+}
+
+void install_signal_handler() {
+  AddVectoredExceptionHandler(0, vectored_handler);
+}
+
+} // namespace mold

lib/siphash.h

@@ -0,0 +1,144 @@
+// This is a header-only C++20 implementation of SipHash based on the
+// reference implementation. To use, just copy this header file into
+// your project and #include it.
+//
+// https://github.com/rui314/siphash/blob/main/siphash.h
+
+#include <bit>
+#include <cstdint>
+#include <cstring>
+
+template <int C_ROUNDS, int D_ROUNDS, int OUTLEN>
+class SipHashTmpl {
+public:
+  static_assert(OUTLEN == 64 || OUTLEN == 128);
+
+  SipHashTmpl(void *key) {
+    uint64_t k0 = read64(key);
+    uint64_t k1 = read64((char *)key + 8);
+
+    v0 = 0x736f6d6570736575 ^ k0;
+    v1 = 0x646f72616e646f6d ^ k1;
+    v2 = 0x6c7967656e657261 ^ k0;
+    v3 = 0x7465646279746573 ^ k1;
+
+    if (OUTLEN == 128)
+      v1 ^= 0xee;
+  }
+
+  void update(void *msgp, int64_t msglen) {
+    char *msg = (char *)msgp;
+    sum += msglen;
+
+    if (buflen) {
+      if (buflen + msglen < 8) {
+        memcpy(buf + buflen, msg, msglen);
+        buflen += msglen;
+        return;
+      }
+
+      int j = 8 - buflen;
+      memcpy(buf + buflen, msg, j);
+      compress(read64(buf));
+
+      msg += j;
+      msglen -= j;
+      buflen = 0;
+    }
+
+    while (msglen >= 8) {
+      compress(read64(msg));
+      msg += 8;
+      msglen -= 8;
+    }
+
+    memcpy(buf, msg, msglen);
+    buflen = msglen;
+  }
+
+  void finish(void *out) {
+    memset(buf + buflen, 0, 8 - buflen);
+    compress(((uint64_t)sum << 56) | read64(buf));
+
+    v2 ^= (OUTLEN == 128) ? 0xee : 0xff;
+    finalize();
+    write64(out, v0 ^ v1 ^ v2 ^ v3);
+
+    if (OUTLEN == 128) {
+      v1 ^= 0xdd;
+      finalize();
+      write64((char *)out + 8, v0 ^ v1 ^ v2 ^ v3);
+    }
+  }
+
+  static void hash(void *out, void *key, void *in, int inlen) {
+    SipHashTmpl<C_ROUNDS, D_ROUNDS, OUTLEN> h(key);
+    h.update(in, inlen);
+    h.finish(out);
+  }
+
+private:
+  uint64_t v0, v1, v2, v3;
+  uint8_t buf[8];
+  uint8_t buflen = 0;
+  uint8_t sum = 0;
+
+  uint64_t read64(void *loc) {
+    uint64_t val;
+    memcpy(&val, loc, 8);
+    if (std::endian::native == std::endian::big)
+      val = bswap(val);
+    return val;
+  }
+
+  void write64(void *loc, uint64_t val) {
+    if (std::endian::native == std::endian::big)
+      val = bswap(val);
+    memcpy(loc, &val, 8);
+  }
+
+  uint64_t bswap(uint64_t val) {
+    return ((val << 56) & 0xff00000000000000) |
+           ((val << 40) & 0x00ff000000000000) |
+           ((val << 24) & 0x0000ff0000000000) |
+           ((val << 8)  & 0x000000ff00000000) |
+           ((val >> 8)  & 0x00000000ff000000) |
+           ((val >> 24) & 0x0000000000ff0000) |
+           ((val >> 40) & 0x000000000000ff00) |
+           ((val >> 56) & 0x00000000000000ff);
+  }
+
+  void round() {
+    v0 += v1;
+    v1 = std::rotl(v1, 13);
+    v1 ^= v0;
+    v0 = std::rotl(v0, 32);
+    v2 += v3;
+    v3 = std::rotl(v3, 16);
+    v3 ^= v2;
+    v0 += v3;
+    v3 = std::rotl(v3, 21);
+    v3 ^= v0;
+    v2 += v1;
+    v1 = std::rotl(v1, 17);
+    v1 ^= v2;
+    v2 = std::rotl(v2, 32);
+  }
+
+  void compress(uint64_t m) {
+    v3 ^= m;
+    for (int i = 0; i < C_ROUNDS; i++)
+      round();
+    v0 ^= m;
+  }
+
+  void finalize() {
+    for (int i = 0; i < D_ROUNDS; i++)
+      round();
+  }
+};
+
+using SipHash = SipHashTmpl<2, 4, 64>;
+using SipHash128 = SipHashTmpl<2, 4, 128>;
+using SipHash13 = SipHashTmpl<1, 3, 64>;
+using SipHash13_128 = SipHashTmpl<1, 3, 128>;

lib/tar.cc

@@ -0,0 +1,114 @@
+// This file contains functions to create a tar file.
+
+#include "common.h"
+
+#ifdef _WIN32
+# define ftruncate _chsize_s
+#endif
+
+namespace mold {
+
+static constexpr i64 BLOCK_SIZE = 512;
+
+// A tar file consists of one or more Ustar header followed by data.
+// Each Ustar header represents a single file in an archive.
+//
+// tar is an old file format, and its `name` field is only 100 bytes long.
+// If `name` is longer than 100 bytes, we can emit a PAX header before a
+// Ustar header to store a long filename.
+//
+// For simplicity, we always emit a PAX header even for a short filename.
+struct UstarHeader {
+  char name[100];
+  char mode[8];
+  char uid[8];
+  char gid[8];
+  char size[12];
+  char mtime[12];
+  char checksum[8];
+  char typeflag[1];
+  char linkname[100];
+  char magic[6];
+  char version[2];
+  char uname[32];
+  char gname[32];
+  char devmajor[8];
+  char devminor[8];
+  char prefix[155];
+  char pad[12];
+};
+
+static_assert(sizeof(UstarHeader) == BLOCK_SIZE);
+
+static void finalize(UstarHeader &hdr) {
+  memset(hdr.checksum, ' ', sizeof(hdr.checksum));
+  memcpy(hdr.magic, "ustar", 5);
+  memcpy(hdr.version, "00", 2);
+
+  // Compute checksum
+  int sum = 0;
+  for (i64 i = 0; i < sizeof(hdr); i++)
+    sum += ((u8 *)&hdr)[i];
+
+  // We need to convince the compiler that sum isn't too big to silence
+  // -Werror=format-truncation.
+  if (sum >= 01'000'000)
+    unreachable();
+  snprintf(hdr.checksum, sizeof(hdr.checksum), "%06o", sum);
+}
+
+static std::string encode_path(std::string basedir, std::string path) {
+  path = path_clean(basedir + "/" + path);
+
+  // Construct a string which contains something like
+  // "16 path=foo/bar\n" where 16 is the size of the string
+  // including the size string itself.
+  i64 len = std::string(" path=\n").size() + path.size();
+  i64 total = std::to_string(len).size() + len;
+  total = std::to_string(total).size() + len;
+  return std::to_string(total) + " path=" + path + "\n";
+}
+
+std::unique_ptr<TarWriter>
+TarWriter::open(std::string output_path, std::string basedir) {
+  FILE *out = fopen(output_path.c_str(), "w");
+  if (!out)
+    return nullptr;
+  return std::unique_ptr<TarWriter>(new TarWriter(out, basedir));
+}
+
+TarWriter::~TarWriter() {
+  fclose(out);
+}
+
+void TarWriter::append(std::string path, std::string_view data) {
+  // Write PAX header
+  UstarHeader pax = {};
+
+  std::string attr = encode_path(basedir, path);
+  snprintf(pax.size, sizeof(pax.size), "%011zo", attr.size());
+  pax.name[0] = '/';
+  pax.typeflag[0] = 'x';
+  finalize(pax);
+  fwrite(&pax, sizeof(pax), 1, out);
+
+  // Write pathname
+  fwrite(attr.data(), attr.size(), 1, out);
+  fseek(out, align_to(ftell(out), BLOCK_SIZE), SEEK_SET);
+
+  // Write Ustar header
+  UstarHeader ustar = {};
+  memcpy(ustar.mode, "0000664", 8);
+  snprintf(ustar.size, sizeof(ustar.size), "%011zo", data.size());
+  finalize(ustar);
+  fwrite(&ustar, sizeof(ustar), 1, out);
+
+  // Write file contents
+  fwrite(data.data(), data.size(), 1, out);
+  fseek(out, align_to(ftell(out), BLOCK_SIZE), SEEK_SET);
+
+  // A tar file must ends with two empty blocks
+  (void)!ftruncate(fileno(out), ftell(out) + BLOCK_SIZE * 2);
+}
+
+} // namespace mold