Google Git
Sign in
llvm / llvm-project / refs/heads/users/MaskRay/spr/main.elf-place-lbsslrodataldata-after-bss
commitce1484089c1271b386a7fe720194796b6263244f[log] [tgz]
authorFangrui Song <i@maskray.me>Tue Feb 20 13:53:29 2024 -0800
committerGitHub <noreply@github.com>Tue Feb 20 13:53:29 2024 -0800
tree8de6c34e5ce03b1da25588bb8e060e5d2adf141f
parent819ebcf2bbc3dfc80f949d4bfebcd1cb797e3a01 [diff]
[ELF] Support placing .lbss/.lrodata/.ldata after .bss (#81224)

https://reviews.llvm.org/D150510 places .lrodata before .rodata to
minimize the number of permission transitions in the memory image.
However, this layout is less ideal for -fno-pic code (which is still
important).

Small code model -fno-pic code has R_X86_64_32S relocations with a range
of `[0,2**31)` (if we ignore the negative area). Placing `.lrodata`
earlier exerts relocation pressure on such code. Non-x86 64-bit
architectures generally have a similar `[0,2**31)` limitation if they
don't use PC-relative relocations.

If we place .lrodata later, we will need one extra PT_LOAD. Two layouts
are appealing:

* .bss/.lbss/.lrodata/.ldata (GNU ld)
* .bss/.ldata/.lbss/.lrodata

The GNU ld layout has the nice property that there is only one BSS
(except .tbss/.relro_padding). Add -z lrodata-after-bss to support
this layout.

Since a read-only PT_LOAD segment (for large data sections) may appear
after RW PT_LOAD segments. The placement of `_etext` has to be adjusted.
6 files changed
tree: 8de6c34e5ce03b1da25588bb8e060e5d2adf141f
  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. openmp/
  21. polly/
  22. pstl/
  23. runtimes/
  24. third-party/
  25. utils/
  26. .arcconfig
  27. .arclint
  28. .clang-format
  29. .clang-tidy
  30. .git-blame-ignore-revs
  31. .gitattributes
  32. .gitignore
  33. .mailmap
  34. CODE_OF_CONDUCT.md
  35. CONTRIBUTING.md
  36. LICENSE.TXT
  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.