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

[Rafael Avila de Espindola via llvm-commits]

Ping. Are you working on this? I really don't think we should have
llvm-ar modifying the files stored in .a in cases it doesn't have to
work around a ld64 bug.

Cheers,
Rafael

Rafael Avila de Espindola <rafael.espindola at gmail.com> writes:

> 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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