[llvm-dev] LLD COFF library: crashes when lld::coff::link is called twice

[Hans Wennborg via llvm-dev]

+Rui and Peter

On Wed, Jul 25, 2018 at 8:34 AM, Andrew Kelley via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Here's a fix:
>
> --- a/lld/COFF/Driver.cpp
> +++ b/lld/COFF/Driver.cpp
> @@ -72,6 +72,9 @@ bool link(ArrayRef<const char *> Args, bool CanExitEarly,
> raw_ostream &Diag) {
>      exitLld(errorCount() ? 1 : 0);
>
>    freeArena();
> +  ObjFile::Instances.clear();
> +  ImportFile::Instances.clear();
> +  BitcodeFile::Instances.clear();
>    return !errorCount();
>  }
>
> I don't know how to make a test for this, since it depends on running LLD
> twice in the same process.
>
> Can I get some assistance trying to get this fix upstreamed?
>
> On Wed, Jul 25, 2018 at 2:18 AM, Andrew Kelley <superjoe30 at gmail.com> wrote:
>>
>> If you call lld::coff::link twice, the second time gives this backtrace:
>>
>>      msvcp140d.dll!00007ffc35830806()    Unknown
>> >    zig.exe!std::_Debug_pointer<lld::coff::Chunk * __ptr64
>> > const>(lld::coff::Chunk * const * _Ptr, const wchar_t * _File, unsigned int
>> > _Line) Line 926    C++
>>      zig.exe!std::_Debug_range2<lld::coff::Chunk * __ptr64 const *
>> __ptr64>(lld::coff::Chunk * const * _First, lld::coff::Chunk * const *
>> _Last, const wchar_t * _File, unsigned int _Line,
>> std::random_access_iterator_tag __formal) Line 958    C++
>>      zig.exe!std::_Debug_range<lld::coff::Chunk * __ptr64 const *
>> __ptr64>(lld::coff::Chunk * const * _First, lld::coff::Chunk * const *
>> _Last, const wchar_t * _File, unsigned int _Line) Line 968    C++
>>      zig.exe!std::vector<lld::coff::Chunk *
>> __ptr64,std::allocator<lld::coff::Chunk * __ptr64>
>> >::_Insert<lld::coff::Chunk * __ptr64 const *
>> __ptr64>(std::_Vector_const_iterator<std::_Vector_val<std::_Simple_types<lld::coff::Chunk
>> *> > > _Where, lld::coff::Chunk * const * _First, lld::coff::Chunk * const *
>> _Last, std::forward_iterator_tag __formal) Line 1421    C++
>>      zig.exe!std::vector<lld::coff::Chunk *
>> __ptr64,std::allocator<lld::coff::Chunk * __ptr64>
>> >::insert<lld::coff::Chunk * __ptr64 const *
>> __ptr64>(std::_Vector_const_iterator<std::_Vector_val<std::_Simple_types<lld::coff::Chunk
>> *> > > _Where, lld::coff::Chunk * const * _First, lld::coff::Chunk * const *
>> _Last) Line 1376    C++
>>      zig.exe!lld::coff::SymbolTable::getChunks() Line 311    C++
>>      zig.exe!`anonymous namespace'::Writer::createSections() Line 340
>> C++
>>      zig.exe!`anonymous namespace'::Writer::run() Line 288    C++
>>      zig.exe!lld::coff::writeResult() Line 166    C++
>>      zig.exe!lld::coff::LinkerDriver::link(llvm::ArrayRef<char const *>
>> ArgsArr) Line 1331    C++
>>      zig.exe!lld::coff::link(llvm::ArrayRef<char const *> Args, bool
>> CanExitEarly, llvm::raw_ostream & Diag) Line 71    C++
>>      zig.exe!ZigLLDLink(ZigLLVM_ObjectFormatType oformat, const char * *
>> args, unsigned __int64 arg_count, void(*)(void *, const char *, unsigned
>> __int64) append_diagnostic, void * context) Line 837    C++
>>      zig.exe!zig_lld_link(ZigLLVM_ObjectFormatType oformat, const char * *
>> args, unsigned __int64 arg_count, Buf * diag) Line 435    C++
>>      zig.exe!codegen_link(CodeGen * g, const char * out_file) Line 1020
>> C++
>>      zig.exe!main(int argc, char * * argv) Line 909    C++
>>      [External Code]
>>
>> It appears that in this code, ObjFile::Instance is garbage data:
>>
>> std::vector<Chunk *> SymbolTable::getChunks() {
>>   std::vector<Chunk *> Res;
>>   for (ObjFile *File : ObjFile::Instances) {
>>     ArrayRef<Chunk *> V = File->getChunks();
>>     Res.insert(Res.end(), V.begin(), V.end());
>>   }
>>   return Res;
>> }
>>
>> When I go to the definition of ObjFile::Instances, it appears to be static
>> data:
>>
>>   static std::vector<ObjFile *> Instances;
>>
>> It appears that LLD is not resetting this data between calls. On the other
>> hand, lld::elf::link and lld::macho::link work no problem when called
>> multiple times in the same process.
>>
>> My understanding is that there is supposed to be an arena allocator, which
>> is freed here:
>>
>> bool link(ArrayRef<const char *> Args, bool CanExitEarly, raw_ostream
>> &Diag) {
>>   // ...
>>
>>   Driver = make<LinkerDriver>();
>>   Driver->link(Args);
>>
>>   // Call exit() if we can to avoid calling destructors.
>>   if (CanExitEarly)
>>     exitLld(errorCount() ? 1 : 0);
>>
>>   freeArena();  // <------ here
>>   return !errorCount();
>> }
>>
>> Is there a simple fix for this?
>>
>> Downstream issue reference: https://github.com/ziglang/zig/issues/1289
>>
>> Thanks,
>> Andrew
>
>
>
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