[PATCH] D96837: Add !retain metadata to represent SHF_GNU_RETAIN on ELF platforms

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
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!retain may be attached to a function/global variable definition.
Its section will be marked as a linker GC root.

We don't restrict the feature to ELFOSABI_GNU and ELFOSABI_FREEBSD for
now. See the rationale in D95749 <https://reviews.llvm.org/D95749>.

The integrated assembler has supported SHF_GNU_RETAIN since D95730 <https://reviews.llvm.org/D95730>.
GNU as>=2.36 supports section flag 'R'.
We don't need to worry about GNU ld support because older GNU ld just ignores
the unknown SHF_GNU_RETAIN.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D96837

Files:
  llvm/docs/LangRef.rst
  llvm/include/llvm/IR/FixedMetadataKinds.def
  llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
  llvm/test/CodeGen/X86/elf-retain.ll

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