[PATCH] D80487: [ELF] Refine --export-dynamic-symbol semantics to be compatible GNU ld 2.35

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: grimar, psmith, ruiu.
Herald added subscribers: llvm-commits, arichardson, emaste.
Herald added a reviewer: espindola.
Herald added a project: LLVM.

GNU ld from binutils 2.35 onwards will likely support
--export-dynamic-symbol but with different semantics.
https://sourceware.org/pipermail/binutils/2020-May/111229.html

Differences:

1. -export-dynamic-symbol is not supported
2. --export-dynamic-symbol takes a glob argument
3. --export-dynamic-symbol can suppress local bind if -shared and (-Bsymbolic or -Bsymbolic-functions)
4. --export-dynamic-symbol does not imply -u

I don't think the first three points can affect any user.
For the first point, Not implying -u can lead to some archive members unfetched.
Some -u foo may be needed.

Exact semantics:

- -no-pie or -pie: symbols matching glob will be added to the dynamic symbol table.
- -shared: matched symbols will not be bound locally (non-preemptible) even if they would otherwise be due to -Bsymbolic, -Bsymbolic-functions, or --dynamic-list.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D80487

Files:
  lld/ELF/Config.h
  lld/ELF/Driver.cpp
  lld/ELF/Options.td
  lld/ELF/ScriptParser.cpp
  lld/ELF/Symbols.cpp
  lld/docs/ReleaseNotes.rst
  lld/docs/ld.lld.1
  lld/test/ELF/export-dynamic-symbol.s
  lld/test/ELF/warn-backrefs.s

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