[all-commits] [llvm/llvm-project] 079429: [llvm-objcopy] Add --compress-sections

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 07942987b58558a8bcb2cfb7d8bc3d46b1cb1d2b
      https://github.com/llvm/llvm-project/commit/07942987b58558a8bcb2cfb7d8bc3d46b1cb1d2b
  Author: Fangrui Song <i at maskray.me>
  Date:   2024-04-15 (Mon, 15 Apr 2024)

  Changed paths:
    M llvm/docs/CommandGuide/llvm-objcopy.rst
    M llvm/docs/ReleaseNotes.rst
    M llvm/include/llvm/ObjCopy/CommonConfig.h
    M llvm/lib/ObjCopy/ELF/ELFObjcopy.cpp
    M llvm/lib/ObjCopy/ELF/ELFObject.cpp
    A llvm/test/tools/llvm-objcopy/ELF/compress-sections-within-segment.s
    A llvm/test/tools/llvm-objcopy/ELF/compress-sections.s
    M llvm/test/tools/llvm-objcopy/ELF/decompress-sections.test
    M llvm/tools/llvm-objcopy/ObjcopyOptions.cpp
    M llvm/tools/llvm-objcopy/ObjcopyOpts.td

  Log Message:
  -----------
  [llvm-objcopy] Add --compress-sections

--compress-sections is similar to --compress-debug-sections but applies
to arbitrary sections.

* `--compress-sections <section>=none`: decompress sections
* `--compress-sections <section>=[zlib|zstd]`: compress sections with zlib/zstd

Like `--remove-section`, the pattern is by default a glob, but a regex
when --regex is specified.

For `--remove-section` like options, `!` prevents matches and is not
dependent on ordering (see `ELF/wildcard-syntax.test`). Since
`--compress-sections a=zlib --compress-sections a=none` naturally allows
overriding, having an order-independent `!` would be confusing.
Therefore, `!` is disallowed.

Sections within a segment are effectively immutable. Report an error for
an attempt to (de)compress them. `SHF_ALLOC` sections in a relocatable
file can be compressed, but linkers usually reject them.

Note: Before this patch, a compressed relocation section is recognized
as a `RelocationSectionBase` as well and `removeSections` `!ToRemove(*ToRelSec)`
may incorrectly interpret a `CompressedSections` as `RelocationSectionBase`,
leading to ubsan failure for the new test. Fix this by setting
`OriginalFlags` in CompressedSection::CompressedSection.

Link: https://discourse.llvm.org/t/rfc-compress-arbitrary-sections-with-ld-lld-compress-sections/71674

Pull Request: https://github.com/llvm/llvm-project/pull/85036



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