[all-commits] [llvm/llvm-project] 66d443: [ELF] Combine foo at v1 and foo with the same version...

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 66d4430492131a2205f159071c15e90c10e2fced
      https://github.com/llvm/llvm-project/commit/66d4430492131a2205f159071c15e90c10e2fced
  Author: Fangrui Song <i at maskray.me>
  Date:   2021-08-04 (Wed, 04 Aug 2021)

  Changed paths:
    M lld/ELF/Driver.cpp
    A lld/test/ELF/symver-non-default.s
    M lld/test/ELF/version-script-symver.s
    M lld/test/ELF/version-symbol-undef.s

  Log Message:
  -----------
  [ELF] Combine foo at v1 and foo with the same versionId if both are defined

Due to an assembler design flaw (IMO), `.symver foo,foo at v1` produces two symbols `foo` and `foo at v1` if `foo` is defined.

* `v1 {};` produces both `foo` and `foo at v1`, but GNU ld only produces `foo at v1`
* `v1 { foo; };` produces both `foo@@v1` and `foo at v1`, but GNU ld only produces `foo at v1`
* `v2 { foo; };` produces both `foo@@v2` and `foo at v1`, matching GNU ld. (Tested by symver.s)

This patch implements the GNU ld behavior by reusing the symbol redirection mechanism
in D92259. The new test symver-non-default.s checks the first two cases.

Without the patch, the second case will produce `foo at v1` and `foo@@v1` which
looks weird and makes foo unnecessarily default versioned.

Note: `.symver foo,foo at v1,remove` exists but the unfortunate `foo` will not go
away anytime soon.

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D107235