IRSymTab: Record _GLOBAL_OFFSET_TABLE_ for ELF x86

In ELF, relocatable files generated for x86-32 and some code models of
x86-64 (medium, large) may reference the special symbol
`_GLOBAL_OFFSET_TABLE_` that is not used in the IR. In an LTO link, if
there is no regular relocatable file referencing the special symbol, the
linker may not define the symbol and lead to a spurious "undefined
symbol" error.

Fix #61101: record that `_GLOBAL_OFFSET_TABLE_` is used in the IR symbol
table.

Note: The `PreservedSymbols` mechanism
(https://reviews.llvm.org/D112595) that just sets `FB_used` is not
applicable.
The `getRuntimeLibcallSymbols` for extracting lazy runtime library
symbols is for symbols that are "always" potentially used, but linkers
don't have the code model information to make a precise decision.

Pull Request: https://github.com/llvm/llvm-project/pull/89463
8 files changed
tree: 3ca5bfe2b7d20cd4ee35df6fd9cc5244863d29db
  1. .ci/
  2. .github/
  3. bolt/
  4. clang/
  5. clang-tools-extra/
  6. cmake/
  7. compiler-rt/
  8. cross-project-tests/
  9. flang/
  10. libc/
  11. libclc/
  12. libcxx/
  13. libcxxabi/
  14. libunwind/
  15. lld/
  16. lldb/
  17. llvm/
  18. llvm-libgcc/
  19. mlir/
  20. offload/
  21. openmp/
  22. polly/
  23. pstl/
  24. runtimes/
  25. third-party/
  26. utils/
  27. .clang-format
  28. .clang-tidy
  29. .git-blame-ignore-revs
  30. .gitattributes
  31. .gitignore
  32. .mailmap
  33. CODE_OF_CONDUCT.md
  34. CONTRIBUTING.md
  35. LICENSE.TXT
  36. pyproject.toml
  37. README.md
  38. SECURITY.md
README.md

The LLVM Compiler Infrastructure

OpenSSF Scorecard OpenSSF Best Practices libc++

Welcome to the LLVM project!

This repository contains the source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and run-time environments.

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 convert them into object files. Tools include an assembler, disassembler, bitcode analyzer, and bitcode optimizer.

C-like languages use the Clang frontend. 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

Consult the Getting Started with LLVM page for information on building and running LLVM.

For information on how to contribute to the LLVM project, please take a look at the Contributing to LLVM guide.

Getting in touch

Join the LLVM Discourse forums, Discord chat, LLVM Office Hours or Regular sync-ups.

The LLVM project has adopted a code of conduct for participants to all modes of communication within the project.