[PATCH] D63309: [llvm-objcopy][MachO] Rebuild the symbol/string table in the writer

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added a comment.
Herald added a subscriber: abrachet.

>From https://developer.apple.com/documentation/kernel/relocation_info?changes=latest_major&language=ob_7:

> r_symbolnum
> 
> Indicates either an index into the symbol table (when the r_extern field is set to 1) or a section number (when the r_extern field is set to 0). As previously mentioned, sections are ordered from 1 to 255 in the order in which they appear in the LC_SEGMENT load commands. This field is set to R_ABS for relocation entries for absolute symbols, which need no relocation.

The current Mach-O reader and writer do not handle r_extern=0 relocations.

  // MachO/MachOReader
  void MachOReader::setSymbolInRelocationInfo(Object &O) const {
    for (auto &LC : O.LoadCommands)
      for (auto &Sec : LC.Sections)
        for (auto &Reloc : Sec.Relocations)
          if (!Reloc.Scattered) {
            auto *Info = reinterpret_cast<MachO::relocation_info *>(&Reloc.Info);
            Reloc.Symbol = O.SymTable.getSymbolByIndex(Info->r_symbolnum);  //// this can reference a section when r_extern=0
          }
  }


Repository:
  rL LLVM

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  https://reviews.llvm.org/D63309/new/

https://reviews.llvm.org/D63309