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llvm / llvm-project / 61069bd5a3954076018ed30c77094d6259bcbc90
commit61069bd5a3954076018ed30c77094d6259bcbc90[log] [tgz]
authorAhmed Bougacha <ahmed@bougacha.org>Fri Jun 14 17:57:12 2024 -0700
committerGitHub <noreply@github.com>Fri Jun 14 17:57:12 2024 -0700
tree22e3b9607aae02c4727fa07b2850d43392027eda
parenta0cef2bf71c5fb7a643656371d8e6cc58271fbe6 [diff]
[Support] Add SipHash-based 16-bit ptrauth ABI-stable hash. (#93902)

This finally wraps the now-lightly-modified SipHash C reference
implementation, for the main interface we need (16-bit ptrauth
discriminators).

The exact algorithm is the little-endian interpretation of the
non-doubled (i.e. 64-bit) result of applying a SipHash-2-4 using the
constant seed `b5d4c9eb79104a796fec8b1b428781d4` (big-endian), with the
result reduced by modulo to the range of non-zero discriminators (i.e.
`(rawHash % 65535) + 1`).

By "stable" we mean that the result of this hash algorithm will the same
across different compiler versions and target platforms.

The 16-bit hashes are used extensively for the AArch64 ptrauth ABI,
because AArch64 can efficiently load a 16-bit immediate into the high
bits of a register without disturbing the remainder of the value, which
serves as a nice blend operation.

16 bits is also sufficiently compact to not inflate a loader relocation.
We disallow zero to guarantee a different discriminator from the places
in the ABI that use a constant zero.

Co-authored-by: John McCall <rjmccall@apple.com>
3 files changed
tree: 22e3b9607aae02c4727fa07b2850d43392027eda
  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

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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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