Build on hosts without 64-bit atomics

std has no AtomicU64 or AtomicI64 on hosts such as 32-bit PowerPC,
32-bit MIPS and pre-v6 ARM, so mold did not compile there, whereas the
C++ version fell back to libatomic. Take those two types from
portable-atomic, which uses the std types where they exist and falls
back to locks elsewhere. Also check the 32-bit PowerPC build in CI; the
existing armv7 check did not catch this because armv7 has 64-bit
atomics.

See https://github.com/rui314/mold/discussions/1643#discussioncomment-18603572.

.github/workflows/ci.yml

@@ -20,10 +20,12 @@ jobs:
         sudo ./install-test-deps.sh
         sudo .github/workflows/install-extras.sh
     - run: cargo build --locked
-    - name: check the build for a 32-bit host
+    - name: check the build for 32-bit hosts
       run: |
-        rustup target add armv7-unknown-linux-gnueabihf
+        rustup target add armv7-unknown-linux-gnueabihf powerpc-unknown-linux-gnu
         cargo check --locked --workspace --all-targets --target armv7-unknown-linux-gnueabihf
+        # 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 |

Cargo.lock

@@ -245,6 +245,7 @@ dependencies = [
  "libz-sys",
  "memchr",
  "memmap2",
+ "portable-atomic",
  "rayon",
  "rustc-demangle",
  "xxhash-rust",
@@ -433,6 +434,12 @@ version = "0.3.34"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f6b464fbc74e149a392436b17d523f769e057cb6877f6a5c4618bc6f11800548"
 
+[[package]]
+name = "portable-atomic"
+version = "1.15.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "05c8b63e8d9609db387f0324918f81d68fe27748f084ef092fb35954d0539a85"
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.107"

Cargo.toml

@@ -36,6 +36,8 @@ 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"
 xxhash-rust = { version = "0.8", features = ["xxh3"] }

src/icf.rs

@@ -65,8 +65,9 @@
 //! conditions.
 
 use std::collections::HashMap;
-use std::sync::atomic::{AtomicU64, Ordering};
+use std::sync::atomic::Ordering;
 
+use portable_atomic::AtomicU64;
 use rayon::prelude::*;
 
 use crate::cmdline::ReportOutput;

src/input_sections.rs

@@ -1,9 +1,10 @@
 //! Input sections and the records the linker parses out of them.
 
 use std::fmt::{self, Write};
-use std::sync::atomic::{AtomicBool, AtomicU8, AtomicU64, Ordering};
+use std::sync::atomic::{AtomicBool, AtomicU8, Ordering};
 
 use bstr::BStr;
+use portable_atomic::AtomicU64;
 
 use crate::chunks::OutputSectionId;
 use crate::chunks::merged::{MergedSection, MergedSectionId};

src/util/perf.rs

@@ -2,10 +2,12 @@
 
 // Counter is used to collect statistics numbers.
 
-use std::sync::atomic::{AtomicBool, AtomicI64, Ordering};
+use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{Arc, Mutex, Once};
 use std::time::Instant;
 
+use portable_atomic::AtomicI64;
+
 use crate::out;
 
 static COUNTERS_ENABLED: AtomicBool = AtomicBool::new(false);