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llvm / llvm-project / lld / e3bd07d10234cb757755c3786cb4595cc4aba941
commite3bd07d10234cb757755c3786cb4595cc4aba941[log] [tgz]
authorFangrui Song <i@maskray.me>Tue Feb 20 13:59:49 2024 -0800
committerCopybara-Service <copybara-worker@google.com>Tue Feb 20 14:02:26 2024 -0800
tree88a3994fe4e3e2f36fd4d4546c56ca9e87e0c9bf
parent9c014ac94c0bfdb05da414ca6a16c882dfd9ce11 [diff]
[ELF] Support placing .lbss/.lrodata/.ldata after .bss

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.

Pull Request: https://github.com/llvm/llvm-project/pull/81224

GitOrigin-RevId: 78762357d449cfcd11426c8e152302a27f2e7d4d
6 files changed
tree: 88a3994fe4e3e2f36fd4d4546c56ca9e87e0c9bf
  1. cmake/
  2. COFF/
  3. Common/
  4. docs/
  5. ELF/
  6. include/
  7. MachO/
  8. MinGW/
  9. test/
  10. tools/
  11. unittests/
  12. utils/
  13. wasm/
  14. .clang-format
  15. .clang-tidy
  16. .gitignore
  17. CMakeLists.txt
  18. CODE_OWNERS.TXT
  19. LICENSE.TXT
  20. README.md
README.md

LLVM Linker (lld)

This directory and its subdirectories contain source code for the LLVM Linker, a modular cross platform linker which is built as part of the LLVM compiler infrastructure project.

lld is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt.

Benchmarking

In order to make sure various developers can evaluate patches over the same tests, we create a collection of self contained programs.

It is hosted at https://s3-us-west-2.amazonaws.com/linker-tests/lld-speed-test.tar.xz

The current sha256 is 10eec685463d5a8bbf08d77f4ca96282161d396c65bd97dc99dbde644a31610f.