[PATCH] D77779: [ELF] Find files relative to the current linker script for INPUT() and GROUP()

[Fangrui Song via Phabricator via llvm-commits]

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

Notation: CWD => current working directory
For a relative pathname in INPUT() or GROUP(),

- GNU ld searches in CWD then in -L
- gold searches in the parent directory of the current linker script then in -L. This behavior makes it convenient to replace a .so or .a with a linker script with additional input.

For example, glibc

  % cat /usr/lib/x86_64-linux-gnu/libm.a
  /* GNU ld script
  */
  OUTPUT_FORMAT(elf64-x86-64)
  GROUP ( /usr/lib/x86_64-linux-gnu/libm-2.29.a /usr/lib/x86_64-linux-gnu/libmvec.a )

could be simplified as `GROUP(libm-2.29.a libmvec.a)`.

This patch changes lld to searches in the parent directory of the current linker script,
next in CWD, then in -L. I filed a feature request for GNU ld: https://sourceware.org/bugzilla/show_bug.cgi?id=25806

I plan to add a configuration which makes libc++.a a linker script:

  INPUT(libc++.a.1 libc++abi.a)

If libc++.a does not include libc++abi.a (or other C++ ABI like libcxxrt.a),
`clang -static -stdlib=libc++` is currently broken (-stdlib= affects
both compiler and linker options).

`clang -static -stdlib=libc++ -lc++abi` translates to `-lc++abi ...
-lc++` which does not work with traditional Unix linkers.

Making libc++.a a linker script is one way to fix `clang -static -stdlib=libc++`
With this feature, libc++.a does not need "relocation" when it is moved
to a different directory..


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D77779

Files:
  lld/ELF/ScriptLexer.h
  lld/ELF/ScriptParser.cpp
  lld/test/ELF/linkerscript/input-relative.s

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