6b0eb5a672
Based on D70020 by serge-sans-paille. The ELF spec says: > Furthermore, there may be internal references among these sections that would not make sense if one of the sections were removed or replaced by a duplicate from another object. Therefore, such groups must be included or omitted from the linked object as a unit. A section cannot be a member of more than one group. GNU ld has 2 behaviors that we don't have: - Group members (nextInSectionGroup != nullptr) are subject to garbage collection. This includes non-SHF_ALLOC SHT_NOTE sections. In particular, discarding non-SHF_ALLOC SHT_NOTE sections is an expected behavior by the Annobin project. See https://developers.redhat.com/blog/2018/02/20/annobin-storing-information-binaries/ for more information. - Groups members are retained or discarded as a unit. Members may have internal references that are not expressed as SHF_LINK_ORDER, relocations, etc. It seems that we should be more conservative here: if a section is marked live, mark all the other member within the group. Both behaviors are reasonable. This patch implements them. A new field InputSectionBase::nextInSectionGroup tracks the next member within a group. on ELF64, this increases sizeof(InputSectionBase) froms 144 to 152. InputSectionBase::dependentSections tracks section dependencies, which is used by both --gc-sections and /DISCARD/. We can't overload it for the "next member" semantic, because we should allow /DISCARD/ to discard sections independent of --gc-sections (GNU ld behavior). This behavior may be reasonably used by `/DISCARD/ : { *(.ARM.exidx*) }` or `/DISCARD/ : { *(.note*) }` (new test `linkerscript/discard-group.s`). Reviewed By: ruiu Differential Revision: https://reviews.llvm.org/D70146 |
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|---|---|---|
| clang | ||
| clang-tools-extra | ||
| compiler-rt | ||
| debuginfo-tests | ||
| libc | ||
| libclc | ||
| libcxx | ||
| libcxxabi | ||
| libunwind | ||
| lld | ||
| lldb | ||
| llgo | ||
| llvm | ||
| openmp | ||
| parallel-libs | ||
| polly | ||
| pstl | ||
| .arcconfig | ||
| .clang-format | ||
| .clang-tidy | ||
| .git-blame-ignore-revs | ||
| .gitignore | ||
| README.md | ||
README.md
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.
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.