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Non-preemptible IFUNC are placed in in.iplt (.glink on EM_PPC64). If there is a non-GOT non-PLT relocation, for pointer equality, we change the type of the symbol from STT_IFUNC and STT_FUNC and bind it to the .glink entry. On EM_386, EM_X86_64, EM_ARM, and EM_AARCH64, the PLT code sequence loads the address from its associated .got.plt slot. An IPLT also has an associated .got.plt slot and can use the same code sequence. On EM_PPC64, the PLT code sequence is actually a bl instruction in .glink . It jumps to `__glink_PLTresolve` (the PLT header). and `__glink_PLTresolve` computes the .plt slot (relocated by R_PPC64_JUMP_SLOT). An IPLT does not have an associated R_PPC64_JUMP_SLOT, so we cannot use `bl` in .iplt . Instead, create a call stub which has a similar code sequence as PPC64PltCallStub. We don't save the TOC pointer, so such scenarios will not work: a function pointer to a non-preemptible ifunc, which resolves to a function defined in another DSO. This is the restriction described by https://sourceware.org/glibc/wiki/GNU_IFUNC (though on many architectures it works in practice): Requirement (a): Resolver must be defined in the same translation unit as the implementations. If an ifunc is taken address but not called, technically we don't need an entry for it, but we currently do that. This patch makes // clang -fuse-ld=lld -fno-pie -no-pie a.c // clang -fuse-ld=lld -fPIE -pie a.c #include <stdio.h> static void impl(void) { puts("meow"); } void thefunc(void) __attribute__((ifunc("resolver"))); void *resolver(void) { return &impl; } int main(void) { thefunc(); void (*theptr)(void) = &thefunc; theptr(); } work on Linux glibc and FreeBSD. Calling a function pointer pointing to a Non-preemptible IFUNC never worked before. Differential Revision: https://reviews.llvm.org/D71509
The LLVM Compiler Infrastructure
This directory and its subdirectories contain source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and runtime environments.
The README briefly describes how to get started with building LLVM. For more information on how to contribute to the LLVM project, please take a look at the Contributing to LLVM guide.
Getting Started with the LLVM System
Taken from https://llvm.org/docs/GettingStarted.html.
Overview
Welcome to the LLVM project!
The LLVM project has multiple components. The core of the project is itself called "LLVM". This contains all of the tools, libraries, and header files needed to process intermediate representations and converts it into object files. Tools include an assembler, disassembler, bitcode analyzer, and bitcode optimizer. It also contains basic regression tests.
C-like languages use the Clang front end. This component compiles C, C++, Objective C, and Objective C++ code into LLVM bitcode -- and from there into object files, using LLVM.
Other components include: the libc++ C++ standard library, the LLD linker, and more.
Getting the Source Code and Building LLVM
The LLVM Getting Started documentation may be out of date. The Clang Getting Started page might have more accurate information.
This is an example workflow and configuration to get and build the LLVM source:
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Checkout LLVM (including related subprojects like Clang):
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git clone https://github.com/llvm/llvm-project.git -
Or, on windows,
git clone --config core.autocrlf=false https://github.com/llvm/llvm-project.git
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Configure and build LLVM and Clang:
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cd llvm-project -
mkdir build -
cd build -
cmake -G <generator> [options] ../llvmSome common generators are:
Ninja--- for generating Ninja build files. Most llvm developers use Ninja.Unix Makefiles--- for generating make-compatible parallel makefiles.Visual Studio--- for generating Visual Studio projects and solutions.Xcode--- for generating Xcode projects.
Some Common options:
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-DLLVM_ENABLE_PROJECTS='...'--- semicolon-separated list of the LLVM subprojects you'd like to additionally build. Can include any of: clang, clang-tools-extra, libcxx, libcxxabi, libunwind, lldb, compiler-rt, lld, polly, or debuginfo-tests.For example, to build LLVM, Clang, libcxx, and libcxxabi, use
-DLLVM_ENABLE_PROJECTS="clang;libcxx;libcxxabi". -
-DCMAKE_INSTALL_PREFIX=directory--- Specify for directory the full pathname of where you want the LLVM tools and libraries to be installed (default/usr/local). -
-DCMAKE_BUILD_TYPE=type--- Valid options for type are Debug, Release, RelWithDebInfo, and MinSizeRel. Default is Debug. -
-DLLVM_ENABLE_ASSERTIONS=On--- Compile with assertion checks enabled (default is Yes for Debug builds, No for all other build types).
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Run your build tool of choice!
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The default target (i.e.
ninjaormake) will build all of LLVM. -
The
check-alltarget (i.e.ninja check-all) will run the regression tests to ensure everything is in working order. -
CMake will generate build targets for each tool and library, and most LLVM sub-projects generate their own
check-<project>target. -
Running a serial build will be slow. To improve speed, try running a parallel build. That's done by default in Ninja; for
make, usemake -j NNN(NNN is the number of parallel jobs, use e.g. number of CPUs you have.)
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For more information see CMake
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Consult the Getting Started with LLVM page for detailed information on configuring and compiling LLVM. You can visit Directory Layout to learn about the layout of the source code tree.