Build the string table using StringTableBuilder, reassign symbol indices, and update symbol indices in relocations to allow adding/modifying/removing symbols from the object.
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I've got several stylistic comments, but don't have time to read up on Mach-O right now to review that aspect of it.
llvm/tools/llvm-objcopy/MachO/MachOWriter.cpp | ||
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124 ↗ | (On Diff #204670) | This shouldn't be auto. |
275 ↗ | (On Diff #204670) | Standard LLVM style says that you should put the end() evaluation in the initializer part of a for loop, unless it can change: for (auto Iter = O.SymTable.Symbols.begin(), End = O.SymTable.Symbols.end(); Iter != End; Iter++) |
277 ↗ | (On Diff #204670) | Can you just make this a raw pointer and do Iter->get()? |
561 ↗ | (On Diff #204670) | Maybe too much auto here. |
llvm/tools/llvm-objcopy/MachO/Object.h | ||
88 ↗ | (On Diff #204670) | Is int the right type here? It seems dubious to me without knowing anything about the file format. |
113 ↗ | (On Diff #204670) | Don't need struct here I believe. |
llvm/tools/llvm-objcopy/MachO/Object.h | ||
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88 ↗ | (On Diff #204670) | I was wrong. This should be uint32_t. Thanks. |
llvm/tools/llvm-objcopy/MachO/MachOReader.cpp | ||
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173 ↗ | (On Diff #205498) | StringRef(StrTable.data() + nlist.n_strx).str() |
186 ↗ | (On Diff #205498) | i think you don't need the explicit specification of the template parameter here, it'll be deduced from the type of the second argument |
llvm/tools/llvm-objcopy/MachO/Object.cpp | ||
10 ↗ | (On Diff #205498) | khm, why is this const_cast needed here ? |
llvm/tools/llvm-objcopy/MachO/Object.h | ||
100 ↗ | (On Diff #205498) | SymbolEntry *getSymbolByIndex(uint32_t Index) const; |
llvm/tools/llvm-objcopy/MachO/Object.h | ||
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227 ↗ | (On Diff #205733) | I'm wondering if MachOWriter would be a better place for StrTableBuilder ? |
llvm/tools/llvm-objcopy/MachO/Object.cpp | ||
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10 ↗ | (On Diff #205498) | First I thought we need to modify something in the SymbolEntry pointed from the RelocationInfo.Symbol, but I realized it is not necessary in this patch. FYI, I used the ELF implementation as reference: class SymbolTableSection : public SectionBase { ... public: const Symbol *getSymbolByIndex(uint32_t Index) const; Symbol *getSymbolByIndex(uint32_t Index); }; |
- Move StrTableBuilder into MachOWriter.
llvm/tools/llvm-objcopy/MachO/Object.h | ||
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227 ↗ | (On Diff #205733) | You're correct! I'll fix this. |
I am getting the compile warnings below when compiling on gcc version 7.3.1.
[1/4] Building CXX object tools/llvm-objcopy/CMakeFiles/llvm-objcopy.dir/MachO/MachOReader.cpp.o /home/anushabasana/local/llvm-project/llvm/tools/llvm-objcopy/MachO/MachOReader.cpp: In instantiation of ‘std::vector<llvm::objcopy::macho::Section> llvm::objcopy::macho::extractSections(const llvm::object::MachOObjectFile::LoadCommandInfo&, const llvm::object::MachOObjectFile&, size_t&) [with SectionType = llvm::MachO::section; SegmentType = llvm::MachO::segment_command; size_t = long unsigned int]’: /home/anushabasana/local/llvm-project/llvm/tools/llvm-objcopy/MachO/MachOReader.cpp:124:46: required from here /home/anushabasana/local/llvm-project/llvm/tools/llvm-objcopy/MachO/MachOReader.cpp:106:17: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing] reinterpret_cast<MachO::scattered_relocation_info *>(&R.Info) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ->r_scattered; ~~^~~~~~~~~~~ /home/anushabasana/local/llvm-project/llvm/tools/llvm-objcopy/MachO/MachOReader.cpp: In instantiation of ‘std::vector<llvm::objcopy::macho::Section> llvm::objcopy::macho::extractSections(const llvm::object::MachOObjectFile::LoadCommandInfo&, const llvm::object::MachOObjectFile&, size_t&) [with SectionType = llvm::MachO::section_64; SegmentType = llvm::MachO::segment_command_64; size_t = long unsigned int]’: /home/anushabasana/local/llvm-project/llvm/tools/llvm-objcopy/MachO/MachOReader.cpp:129:50: required from here /home/anushabasana/local/llvm-project/llvm/tools/llvm-objcopy/MachO/MachOReader.cpp:106:17: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
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 } }