llvm dev - Jul 2018 - LLD COFF library: crashes when lld::coff::link is called twice

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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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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+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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