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llvm / llvm-project / e665cf397686e881cfb0728d896d2f375c0aead5
commite665cf397686e881cfb0728d896d2f375c0aead5[log] [tgz]
authorMaksim Panchenko <maks@fb.com>Mon Aug 25 17:13:30 2025 -0700
committerGitHub <noreply@github.com>Mon Aug 25 17:13:30 2025 -0700
tree8ba0eaa010aa408c9ec4160952984b8a17c20284
parentdc8596d5485a52abee2967cec72f81ef4872270c [diff]
[BOLT] Fix handling of ambiguous jump table entries (#155291)

Jump tables may contain entries that point immediately past the end of
their parent function. Normally, such entries are generated by the
compiler as a result of builtin_unreachable() case. We used to replace
those entries with a label belonging to their parent function assuming
the destination doesn't matter if it's an undefined behavior.

However, if such entry is at the end of the jump table, it could be a
real function pointer, not a jump table entry. We rely on heuristics to
detect such cases and can drop the trailing function pointer entries
from the table.

The problem presents when the "unreachable" ambiguous entry is followed
by another ambiguous entry corresponding to the start of the parent
function. In this case we accept pointers as entries and may incorrectly
update the function pointer.

The solution is to keep ambiguous "unreachable" jump table entries
identical to the original input, i.e. point to the same function. This
change does not affect CFG, but results in the entries being updated
with the new function address if it gets relocated.
4 files changed
tree: 8ba0eaa010aa408c9ec4160952984b8a17c20284
  1. .ci/
  2. .github/
  3. bolt/
  4. clang/
  5. clang-tools-extra/
  6. cmake/
  7. compiler-rt/
  8. cross-project-tests/
  9. flang/
  10. flang-rt/
  11. libc/
  12. libclc/
  13. libcxx/
  14. libcxxabi/
  15. libsycl/
  16. libunwind/
  17. lld/
  18. lldb/
  19. llvm/
  20. llvm-libgcc/
  21. mlir/
  22. offload/
  23. openmp/
  24. orc-rt/
  25. polly/
  26. runtimes/
  27. third-party/
  28. utils/
  29. .clang-format
  30. .clang-format-ignore
  31. .clang-tidy
  32. .git-blame-ignore-revs
  33. .gitattributes
  34. .gitignore
  35. .mailmap
  36. CODE_OF_CONDUCT.md
  37. CONTRIBUTING.md
  38. LICENSE.TXT
  39. pyproject.toml
  40. README.md
  41. SECURITY.md
README.md

The LLVM Compiler Infrastructure

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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.

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

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