[lld] r194349 - [ELF] Un-break undef-from-main-dso.test on MSVC 2012.

[Chandler Carruth]

On Sun, Nov 10, 2013 at 12:06 AM, Rui Ueyama <ruiu at google.com> wrote:

> What was proposed? Is that something that might have helped me find the
> issue? It actually took a whole day to find it and workaround, so any help
> would have been appreciated...
>

I'm not sure we have looked at anything that would have helped in this
specific case. =/

Essentially, when Warren was working on the record layout in Clang to be
compatible with MSVC he found a lot of cases where the behavior might be
"buggy" from the perspective of the application developer. We'd like to
have warnings in Clang for when these situations arise, but haven't yet
implemented them.


>
>
> On Sat, Nov 9, 2013 at 11:56 PM, Chandler Carruth <chandlerc at google.com>wrote:
>
>> This commit might help motivate the warnings we've discussed surrounding
>> MSVC record layout...
>>
>>
>> On Sat, Nov 9, 2013 at 11:48 PM, Rui Ueyama <ruiu at google.com> wrote:
>>
>>> Author: ruiu
>>> Date: Sun Nov 10 01:48:33 2013
>>> New Revision: 194349
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=194349&view=rev
>>> Log:
>>> [ELF] Un-break undef-from-main-dso.test on MSVC 2012.
>>>
>>> The result of sizeof(SymbolTable<ELFT>::SymbolEntry) in
>>> DynamicSymbolTable
>>> <ELFT>::write() was different from the same expression in RelocationTable
>>> <ELFT>::write(), although the same template parameters were passed. They
>>> were
>>> 40 and 32, respectively. As a result, the same vector was treated as a
>>> vector of 40 byte values in some places and a vector of 32 values in
>>> other
>>> places. That caused an weird issue, resulting in collapse of the rela.dyn
>>> section.
>>>
>>> I suspect that this is a padding size calculation bug in MSVC 2012, but I
>>> may be wrong. Reordering the fields to eliminate padding seems to fix the
>>> issue.
>>>
>>> Modified:
>>>     lld/trunk/lib/ReaderWriter/ELF/SectionChunks.h
>>>
>>> Modified: lld/trunk/lib/ReaderWriter/ELF/SectionChunks.h
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/ELF/SectionChunks.h?rev=194349&r1=194348&r2=194349&view=diff
>>>
>>> ==============================================================================
>>> --- lld/trunk/lib/ReaderWriter/ELF/SectionChunks.h (original)
>>> +++ lld/trunk/lib/ReaderWriter/ELF/SectionChunks.h Sun Nov 10 01:48:33
>>> 2013
>>> @@ -614,12 +614,12 @@ class SymbolTable : public Section<ELFT>
>>>    struct SymbolEntry {
>>>      SymbolEntry(const Atom *a, const Elf_Sym &sym,
>>>                  const lld::AtomLayout *layout)
>>> -        : _atom(a), _symbol(sym), _atomLayout(layout) {}
>>> +        : _atom(a), _atomLayout(layout), _symbol(sym) {}
>>>      SymbolEntry() : _atom(nullptr) {}
>>>
>>>      const Atom *_atom;
>>> -    Elf_Sym _symbol;
>>>      const lld::AtomLayout *_atomLayout;
>>> +    Elf_Sym _symbol;
>>>    };
>>>
>>>  public:
>>>
>>>
>>> _______________________________________________
>>> llvm-commits mailing list
>>> llvm-commits at cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>>>
>>
>>
>
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