[lld] r301833 - Add comments about how we handle mergeable sections with relocations.

[Rafael Avila de Espindola via llvm-commits]

Thanks!

Rui Ueyama via llvm-commits <llvm-commits at lists.llvm.org> writes:

> Author: ruiu
> Date: Mon May  1 15:49:09 2017
> New Revision: 301833
>
> URL: http://llvm.org/viewvc/llvm-project?rev=301833&view=rev
> Log:
> Add comments about how we handle mergeable sections with relocations.
>
> Also factored out code.
>
> Modified:
>     lld/trunk/ELF/InputFiles.cpp
>
> Modified: lld/trunk/ELF/InputFiles.cpp
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputFiles.cpp?rev=301833&r1=301832&r2=301833&view=diff
> ==============================================================================
> --- lld/trunk/ELF/InputFiles.cpp (original)
> +++ lld/trunk/ELF/InputFiles.cpp Mon May  1 15:49:09 2017
> @@ -361,6 +361,15 @@ InputSectionBase *elf::ObjectFile<ELFT>:
>    return Target;
>  }
>  
> +// Create a regular InputSection class that has the same contents
> +// as a given section.
> +InputSectionBase *toRegularSection(MergeInputSection *Sec) {
> +  auto *Ret = make<InputSection>(Sec->Flags, Sec->Type, Sec->Alignment,
> +                                 Sec->Data, Sec->Name);
> +  Ret->File = Sec->File;
> +  return Ret;
> +}
> +
>  template <class ELFT>
>  InputSectionBase *
>  elf::ObjectFile<ELFT>::createInputSection(const Elf_Shdr &Sec,
> @@ -398,12 +407,15 @@ elf::ObjectFile<ELFT>::createInputSectio
>      if (Target->FirstRelocation)
>        fatal(toString(this) +
>              ": multiple relocation sections to one section are not supported");
> -    if (isa<MergeInputSection>(Target)) {
> -      this->Sections[Sec.sh_info] =
> -          make<InputSection>(Target->Flags, Target->Type, Target->Alignment,
> -                             Target->Data, Target->Name);
> -      this->Sections[Sec.sh_info]->File = Target->File;
> -      Target = this->Sections[Sec.sh_info];
> +
> +    // Mergeable sections with relocations are tricky because relocations
> +    // need to be taken into account when comparing section contents for
> +    // merging. The MergeInputSection class currently doesn't care about
> +    // relocations, and it's unlikely to support it in future because such
> +    // sections are rare. We simply handle such sections as non-mergeable.
> +    if (auto *MS = dyn_cast<MergeInputSection>(Target)) {
> +      Target = toRegularSection(MS);
> +      this->Sections[Sec.sh_info] = Target;
>      }
>  
>      size_t NumRelocations;
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits