[PATCH] D94323: [dsymutil] Support finding relocations in debug_addr for DWARF5

[Alexey Lapshin via Phabricator via llvm-commits]

avl added a comment.

If I understood correctly, It looks like this change is not enough to work properly for DWARF5.
Currently, relocation is checked using offsets to the attribute:

  bool DwarfLinkerForBinary::AddressManager::hasLiveAddressRange(
      const DWARFDie &DIE, CompileUnit::DIEInfo &MyInfo) {
    const auto *Abbrev = DIE.getAbbreviationDeclarationPtr();
  
    Optional<uint32_t> LowPcIdx = Abbrev->findAttributeIndex(dwarf::DW_AT_low_pc);
    if (!LowPcIdx)
      return false;
  
    uint64_t Offset = DIE.getOffset() + getULEB128Size(Abbrev->getCode());
    uint64_t LowPcOffset, LowPcEndOffset;
    std::tie(LowPcOffset, LowPcEndOffset) =
        getAttributeOffsets(Abbrev, *LowPcIdx, Offset, *DIE.getDwarfUnit());
  
    return hasValidRelocationAt(LowPcOffset, LowPcEndOffset, MyInfo);   <<<< check relocation inside debug_info
  }

i.e. we check whether relocation exists between LowPcOffset, LowPcEndOffset of dwarf::DW_AT_low_pc inside debug_info table.

If we would read relocations for "debug_addr" table instead of the "debug_info" table then we would check the wrong relocations. To work properly we would need to recognize offset inside "debug_addr". Something like this(I did not check whether it could be compiled or whether it is full enough):

  Optional<uint32_t> LowPcIdx = Abbrev->findAttributeIndex(dwarf::DW_AT_low_pc);
  if (!LowPcIdx)
    return false;
  
  if ( Abbrev->getFormByIndex(*LowPcIdx) == DW_FORM_addr ) {
    uint64_t Offset = DIE.getOffset() + getULEB128Size(Abbrev->getCode());
    uint64_t LowPcOffset, LowPcEndOffset;
    std::tie(LowPcOffset, LowPcEndOffset) =
      getAttributeOffsets(Abbrev, *LowPcIdx, Offset, *DIE.getDwarfUnit());
  
    return hasValidRelocationAt(LowPcOffset, LowPcEndOffset, MyInfo); <<<< check relocations inside debug_info
  } else ( Abbrev->getFormByIndex(*LowPcIdx) == DW_FORM_addrx) {
    Optional<DWARFFormValue> OffsetValue = DIE.find(dwarf::DW_AT_low_pc);
    if (OffsetValue) {
      uint64_t LowPcOffset = OffsetValue->getRawUValue();
      uint64_t LowPcEndOffset = LowPcOffset + 4;
      return hasValidRelocationAt(LowPcOffset, LowPcEndOffset, MyInfo); <<<< check relocations inside debug_addr
    }
  }

i.e. in case when we do "findValidRelocs(Section, Obj, DMO)" for "debug_addr" then we need to use other offsets(LowPcOffset/LowPcEndOffset) inside hasLiveMemoryLocation/hasLiveAddressRange.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D94323/new/

https://reviews.llvm.org/D94323