[lld] r250463 - ELF2: Do not treat .strtab specially when creating sections.

[Rafael Espíndola via llvm-commits]

Hi,

This and previous patches add more walks over all the output sections.

A normal file normally has less than 100 output sections, so this is
not normally a problem, but it is possible to craft a file with an
arbitrary large number of output sections. I am not sure if we care
about it or not. I just wanted to make sure you know about the
possibility.

Cheers,
Rafael



On 15 October 2015 at 17:50, Rui Ueyama via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: ruiu
> Date: Thu Oct 15 16:50:30 2015
> New Revision: 250463
>
> URL: http://llvm.org/viewvc/llvm-project?rev=250463&view=rev
> Log:
> ELF2: Do not treat .strtab specially when creating sections.
>
> String table is added to end of the file so that all the other sections
> are finalized before string table. But we can just add section names to
> the string table before calling finalize() on any section instead.
>
> Modified:
>     lld/trunk/ELF/Writer.cpp
>
> Modified: lld/trunk/ELF/Writer.cpp
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=250463&r1=250462&r2=250463&view=diff
> ==============================================================================
> --- lld/trunk/ELF/Writer.cpp (original)
> +++ lld/trunk/ELF/Writer.cpp Thu Oct 15 16:50:30 2015
> @@ -470,7 +470,10 @@ template <class ELFT> void Writer<ELFT>:
>    }
>    addCommonSymbols(CommonSymbols);
>
> +  // This order is not the same as the final output order
> +  // because we sort the sections using their attributes below.
>    OutputSections.push_back(Out<ELFT>::SymTab);
> +  OutputSections.push_back(Out<ELFT>::StrTab);
>    if (isOutputDynamic()) {
>      OutputSections.push_back(Out<ELFT>::DynSymTab);
>      OutputSections.push_back(Out<ELFT>::HashTab);
> @@ -487,21 +490,19 @@ template <class ELFT> void Writer<ELFT>:
>    std::stable_sort(OutputSections.begin(), OutputSections.end(),
>                     compareOutputSections<ELFT>);
>
> -  // Always put StrTabSec last so that no section names are added to it after
> -  // it's finalized.
> -  OutputSections.push_back(Out<ELFT>::StrTab);
> -
>    for (unsigned I = 0, N = OutputSections.size(); I < N; ++I)
>      OutputSections[I]->SectionIndex = I + 1;
>
> -  // Fill the DynStrTab early.
> +  for (OutputSectionBase<ELFT::Is64Bits> *Sec : OutputSections)
> +    Out<ELFT>::StrTab->add(Sec->getName());
> +
> +  // Fill the DynStrTab early because Dynamic adds strings to
> +  // DynStrTab but .dynstr may appear before .dynamic.
>    Out<ELFT>::Dynamic->finalize();
>
> -  // Fix each section's header (e.g. sh_size, sh_link, etc.)
> -  for (OutputSectionBase<ELFT::Is64Bits> *Sec : OutputSections) {
> -    Out<ELFT>::StrTab->add(Sec->getName());
> +  // Fill other section headers.
> +  for (OutputSectionBase<ELFT::Is64Bits> *Sec : OutputSections)
>      Sec->finalize();
> -  }
>
>    // If we have a .opd section (used under PPC64 for function descriptors),
>    // store a pointer to it here so that we can use it later when processing
>
>
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