[all-commits] [llvm/llvm-project] c10218: [ELF] Synthesize STT_FILE if necessary (#209087)

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: c102184cbdcb8467ce1caf384ecd4e36d97fa37c
      https://github.com/llvm/llvm-project/commit/c102184cbdcb8467ce1caf384ecd4e36d97fa37c
  Author: Fangrui Song <i at maskray.me>
  Date:   2026-07-15 (Wed, 15 Jul 2026)

  Changed paths:
    M lld/ELF/SyntheticSections.cpp
    M lld/ELF/SyntheticSections.h
    M lld/ELF/Writer.cpp
    M lld/test/ELF/local-symbols-order.s
    M lld/test/ELF/lto/parallel-internalize.ll
    M lld/test/ELF/ppc64-local-entry.s
    M lld/test/ELF/relocatable-comdat-multiple.s
    M lld/test/ELF/relocatable-comdat2.s
    M lld/test/ELF/relocatable-discard-locals.s
    M lld/test/ELF/relocatable-gc.s
    M lld/test/ELF/relocatable.s
    M lld/test/ELF/strtab-nodedup.s

  Log Message:
  -----------
  [ELF] Synthesize STT_FILE if necessary (#209087)

lld groups local symbols in .symtab by input file, appending a symbol
converted to STB_LOCAL (hidden visibility, version script `local:`, or
--exclude-libs) to its file's group. The nearest preceding STT_FILE then
claims the symbol, but the attribution can be wrong: the file may
contain multiple STT_FILE symbols (-r output), or lack an STT_FILE for
the symbol's unit.

```
FILE    LOCAL  DEFAULT   ABS a.c
NOTYPE  LOCAL  DEFAULT     7 a_local
FILE    LOCAL  DEFAULT   ABS b.c
NOTYPE  LOCAL  DEFAULT     7 b_local
NOTYPE  LOCAL  DEFAULT     7 a_localized
```

Follow GNU ld:

- If the output contains an STT_FILE symbol, place at the end of the
  local part, after a synthetic STT_FILE with an empty name, every local
  that cannot be attributed to a file: symbols converted to STB_LOCAL,
  linker-synthesized symbols such as `_DYNAMIC`, and range-extension
  thunks (parented to the internal file, which has no STT_FILE).
- For -r output, synthesize an STT_FILE named after the input file for
an input that outputs local symbols but no STT_FILE, so that its locals
  are not attributed to a preceding file. We use the basename instead of
  the full name for local determinism (#47367).

GNU ld synthesizes this per-input STT_FILE for executable and
shared-object output as well. Restrict it to -r for now to minimize test
updates.

Close #47367 and #191478



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