[lld] r268945 - Document and test the first few .got.plt entries.

[Sean Silva via llvm-commits]

On Mon, May 9, 2016 at 11:12 AM, Rafael Espindola via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: rafael
> Date: Mon May  9 13:12:15 2016
> New Revision: 268945
>
> URL: http://llvm.org/viewvc/llvm-project?rev=268945&view=rev
> Log:
> Document and test the first few .got.plt entries.
>
> Added:
>     lld/trunk/test/ELF/got-plt-header.s
> Modified:
>     lld/trunk/ELF/Target.cpp
>     lld/trunk/ELF/Target.h
>
> Modified: lld/trunk/ELF/Target.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Target.cpp?rev=268945&r1=268944&r2=268945&view=diff
>
> ==============================================================================
> --- lld/trunk/ELF/Target.cpp (original)
> +++ lld/trunk/ELF/Target.cpp Mon May  9 13:12:15 2016
> @@ -531,6 +531,10 @@ RelExpr X86_64TargetInfo::getRelExpr(uin
>  }
>
>  void X86_64TargetInfo::writeGotPltHeader(uint8_t *Buf) const {
> +  // The first entry holds the value of _DYNAMIC. It is not clear why
> that is
> +  // required, but it is documented in the psabi and the glibc dynamic
> linker
> +  // seems to use it (not that this is relevant for linking ld.so, not any
> +  // other program).
>

Could you reword "not that this is relevant for linking ld.so, not any
other program"? There's something awkward about the two "not"'s.

-- Sean Silva


>    write64le(Buf, Out<ELF64LE>::Dynamic->getVA());
>  }
>
>
> Modified: lld/trunk/ELF/Target.h
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Target.h?rev=268945&r1=268944&r2=268945&view=diff
>
> ==============================================================================
> --- lld/trunk/ELF/Target.h (original)
> +++ lld/trunk/ELF/Target.h Mon May  9 13:12:15 2016
> @@ -78,7 +78,11 @@ public:
>    uint32_t TlsOffsetRel;
>    unsigned PltEntrySize = 8;
>    unsigned PltZeroSize = 0;
> +
> +  // At least on x86_64 positions 1 and 2 are used by the first plt entry
> +  // to support lazy loading.
>    unsigned GotPltHeaderEntriesNum = 3;
> +
>    uint32_t ThunkSize = 0;
>    bool UseLazyBinding = false;
>
>
> Added: lld/trunk/test/ELF/got-plt-header.s
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/got-plt-header.s?rev=268945&view=auto
>
> ==============================================================================
> --- lld/trunk/test/ELF/got-plt-header.s (added)
> +++ lld/trunk/test/ELF/got-plt-header.s Mon May  9 13:12:15 2016
> @@ -0,0 +1,30 @@
> +// RUN: llvm-mc %s -o %t.o -filetype=obj -triple=x86_64-pc-linux
> +// RUN: ld.lld %t.o -o %t.so -shared
> +// RUN: llvm-readobj -s -section-data %t.so | FileCheck %s
> +
> +        call foo at plt
> +
> +// Check that the first .got.plt entry has the address of the dynamic
> table.
> +
> +// CHECK:      Type: SHT_DYNAMIC
> +// CHECK-NEXT: Flags [
> +// CHECK-NEXT:   SHF_ALLOC
> +// CHECK-NEXT:   SHF_WRITE
> +// CHECK-NEXT: ]
> +// CHECK-NEXT: Address: 0x2000
> +
> +// CHECK:      Name: .got.plt
> +// CHECK-NEXT: Type: SHT_PROGBITS
> +// CHECK-NEXT: Flags [
> +// CHECK-NEXT:   SHF_ALLOC
> +// CHECK-NEXT:   SHF_WRITE
> +// CHECK-NEXT: ]
> +// CHECK-NEXT: Address: 0x3000
> +// CHECK-NEXT: Offset: 0x3000
> +// CHECK-NEXT: Size: 32
> +// CHECK-NEXT: Link: 0
> +// CHECK-NEXT: Info: 0
> +// CHECK-NEXT: AddressAlignment: 8
> +// CHECK-NEXT: EntrySize: 0
> +// CHECK-NEXT: SectionData (
> +// CHECK-NEXT:   0000: 00200000 00000000 00000000 00000000
>
>
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