[llvm] r294615 - Object: pad out BSD archive members to 8-bytes

[Rafael Avila de Espindola via llvm-commits]

I am pretty sure this is working around a bug in ld64.

We were already aligning the objects themselves. There is no point in
requiring the member header to be aligned.

Also, this has the *very* bad property that the file you put in the .a
is not the file you get out: it might have '\n' added to the end.

If we absolutely must do this, we should add a new archive format
(K_APPLE?). We already check if we are adding macho files to the
archive, so we could use that.

Cheers,
Rafael


Saleem Abdulrasool via llvm-commits <llvm-commits at lists.llvm.org>
writes:

> Author: compnerd
> Date: Thu Feb  9 13:29:35 2017
> New Revision: 294615
>
> URL: http://llvm.org/viewvc/llvm-project?rev=294615&view=rev
> Log:
> Object: pad out BSD archive members to 8-bytes
>
> ld64 requires its archive members to be 8-byte aligned for 64-bit
> content and 4-byte aligned for 32-bit content.  Opt for the larger
> alignment requirement.  This ensures that ld64 can consume archives
> generated by llvm-ar.
>
> Thanks to Kevin Enderby for the hint about the ld64/cctools behaviours!
>
> Resolves PR28361!
>
> Modified:
>     llvm/trunk/lib/Object/ArchiveWriter.cpp
>     llvm/trunk/test/Object/archive-format.test
>
> Modified: llvm/trunk/lib/Object/ArchiveWriter.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Object/ArchiveWriter.cpp?rev=294615&r1=294614&r2=294615&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Object/ArchiveWriter.cpp (original)
> +++ llvm/trunk/lib/Object/ArchiveWriter.cpp Thu Feb  9 13:29:35 2017
> @@ -395,18 +395,28 @@ llvm::writeArchive(StringRef ArcName,
>    std::vector<unsigned> MemberOffset;
>    for (const NewArchiveMember &M : NewMembers) {
>      MemoryBufferRef File = M.Buf->getMemBufferRef();
> +    unsigned Padding = 0;
>  
>      unsigned Pos = Out.tell();
>      MemberOffset.push_back(Pos);
>  
> +    // ld64 expects the members to be 8-byte aligned for 64-bit content and at
> +    // least 4-byte aligned for 32-bit content.  Opt for the larger encoding
> +    // uniformly.  This matches the behaviour with cctools and ensures that ld64
> +    // is happy with archives that we generate.
> +    if (Kind == object::Archive::K_BSD)
> +      Padding = OffsetToAlignment(M.Buf->getBufferSize(), 8);
> +
>      printMemberHeader(Out, Kind, Thin,
>                        sys::path::filename(M.Buf->getBufferIdentifier()),
>                        StringMapIndexIter, M.ModTime, M.UID, M.GID, M.Perms,
> -                      M.Buf->getBufferSize());
> +                      M.Buf->getBufferSize() + Padding);
>  
>      if (!Thin)
>        Out << File.getBuffer();
>  
> +    while (Padding--)
> +      Out << '\n';
>      if (Out.tell() % 2)
>        Out << '\n';
>    }
>
> Modified: llvm/trunk/test/Object/archive-format.test
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Object/archive-format.test?rev=294615&r1=294614&r2=294615&view=diff
> ==============================================================================
> --- llvm/trunk/test/Object/archive-format.test (original)
> +++ llvm/trunk/test/Object/archive-format.test Thu Feb  9 13:29:35 2017
> @@ -32,10 +32,12 @@ RUN: llvm-ar --format=bsd rc %t.a 012345
>  RUN: cat %t.a | FileCheck -strict-whitespace --check-prefix=BSD %s
>  
>  BSD:      !<arch>
> -BSD-NEXT: #1/20           0           0     0     644     24        `
> -BSD-NEXT: 0123456789abcde{{.....}}bar.
> -BSD-SAME: #1/16           0           0     0     644     20        `
> -BSD-NEXT: 0123456789abcdefzed.
> +BSD-NEXT: #1/20           0           0     0     644     28        `
> +Each [[:space:]] matches a newline.  We explicitly match 3 newlines, as the
> +fourth newline is implicitly consumed by FileCheck and cannot be matched.
> +BSD-NEXT: 0123456789abcde{{.....}}bar.{{[[:space:]][[:space:]][[:space:]]}}
> +BSD-NEXT: #1/20           0           0     0     644     28        `
> +BSD-NEXT: 0123456789abcdef{{....}}zed.
>  
>  RUN: rm -f test.a
>  RUN: llvm-ar --format=gnu rcT test.a 0123456789abcde 0123456789abcdef
>
>
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