[PATCH] D91152: [obj2yaml] - Dump section offsets in some cases.

[George Rimar via Phabricator via llvm-commits]

grimar added a comment.

In D91152#2388491 <https://reviews.llvm.org/D91152#2388491>, @jhenderson wrote:

> Doesn't the behaviour of a SHT_NOBITS section depend on whether it is a non-last member of a segment? IIRC, SHT_NOBITS sections in a segment which are last do not need file space, but to ensure correct addresses for sections appearing after them in a segment, they are allocated filespace by a linker if non-NOBITS appear after them in the same segment. (The behaviour you're doing here looks fine for when such sections are not inside segments, e.g. for ET_REL objects).

True. But how much necessary to support this case now? The problem is that we at first dump sections and then dump program headers.
To implement the precise behavior, I think we need to delay assigning offsets to be able to call `shouldAllocateFileSpace`, which does the job:

  static bool shouldAllocateFileSpace(ArrayRef<ELFYAML::ProgramHeader> Phdrs,
                                      const ELFYAML::NoBitsSection &S) {
    for (const ELFYAML::ProgramHeader &PH : Phdrs) {
      auto It = llvm::find_if(
          PH.Chunks, [&](ELFYAML::Chunk *C) { return C->Name == S.Name; });
      if (std::any_of(It, PH.Chunks.end(), [](ELFYAML::Chunk *C) {
            return (isa<ELFYAML::Fill>(C) ||
                    cast<ELFYAML::Section>(C)->Type != ELF::SHT_NOBITS);
          }))
        return true;
    }
    return false;
  }

I wonder - do we want adding this complexity? I thought that nobits sections are usually placed after progbits anyways.


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