[lld] r280630 - [ELF][MIPS] Do not emit DT_REL[A]COUNT for MIPS targets

[Rafael Espíndola via llvm-commits]

"does not support" sounds like it would just ignore the tag, which is
fine. Do you mean that it refuses to load DSOs with the tag present?

Cheers,
Rafael


On 4 September 2016 at 13:40, Simon Atanasyan via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: atanasyan
> Date: Sun Sep  4 12:40:12 2016
> New Revision: 280630
>
> URL: http://llvm.org/viewvc/llvm-project?rev=280630&view=rev
> Log:
> [ELF][MIPS] Do not emit DT_REL[A]COUNT for MIPS targets
>
> It looks like MIPS dynamic loader does not support RELCOUNT tag.
> Both gold/bfd linkers does not emit this tag on MIPS. I will investigate
> the problem further but for now it is better to behave like GNU linkers.
>
> Modified:
>     lld/trunk/ELF/OutputSections.cpp
>     lld/trunk/test/ELF/mips-32.s
>
> Modified: lld/trunk/ELF/OutputSections.cpp
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/OutputSections.cpp?rev=280630&r1=280629&r2=280630&view=diff
> ==============================================================================
> --- lld/trunk/ELF/OutputSections.cpp (original)
> +++ lld/trunk/ELF/OutputSections.cpp Sun Sep  4 12:40:12 2016
> @@ -671,9 +671,14 @@ template <class ELFT> void DynamicSectio
>      Add({IsRela ? DT_RELAENT : DT_RELENT,
>           uintX_t(IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel))});
>
> -    size_t NumRelativeRels = Out<ELFT>::RelaDyn->getRelativeRelocCount();
> -    if (Config->ZCombreloc && NumRelativeRels)
> -      Add({IsRela ? DT_RELACOUNT : DT_RELCOUNT, NumRelativeRels});
> +    // MIPS dynamic loader does not support RELCOUNT tag.
> +    // The problem is in the tight relation between dynamic
> +    // relocations and GOT. So do not emit this tag on MIPS.
> +    if (Config->EMachine != EM_MIPS) {
> +      size_t NumRelativeRels = Out<ELFT>::RelaDyn->getRelativeRelocCount();
> +      if (Config->ZCombreloc && NumRelativeRels)
> +        Add({IsRela ? DT_RELACOUNT : DT_RELCOUNT, NumRelativeRels});
> +    }
>    }
>    if (Out<ELFT>::RelaPlt && Out<ELFT>::RelaPlt->hasRelocs()) {
>      Add({DT_JMPREL, Out<ELFT>::RelaPlt});
>
> Modified: lld/trunk/test/ELF/mips-32.s
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/mips-32.s?rev=280630&r1=280629&r2=280630&view=diff
> ==============================================================================
> --- lld/trunk/test/ELF/mips-32.s (original)
> +++ lld/trunk/test/ELF/mips-32.s Sun Sep  4 12:40:12 2016
> @@ -52,10 +52,11 @@ v2:
>  # REL-NEXT:   }
>  # REL-NEXT: ]
>
> -# REL: DynamicSection [
> -# REL:   Tag        Type                 Name/Value
> -# REL:   0x00000012 RELSZ                16 (bytes)
> -# REL:   0x00000013 RELENT               8 (bytes)
> +# REL:   DynamicSection [
> +# REL:     Tag        Type                 Name/Value
> +# REL:     0x00000012 RELSZ                16 (bytes)
> +# REL:     0x00000013 RELENT               8 (bytes)
> +# REL-NOT: 0x6FFFFFFA RELCOUNT
>
>  # REL:      Primary GOT {
>  # REL-NEXT:   Canonical gp value:
>
>
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