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[MinGW] Clang issues with static libstdc++

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[MinGW] Clang issues with static libstdc++

Brian Cain via cfe-dev

Clang doesn't work very well with static libstdc++ build for MinGW resulting in "multiple definition ..." or "undefined reference" to the symbols.

Let's consider following code (removed includes and main for readability):

  1. multiple definition:

    std::string a = "a";
    std::string b = '@' + a;

    This simple code build with `-static` flag will cause this error:

    D:\msys64\mingw64\lib\gcc\x86_64-w64-mingw32\6.3.0\libstdc++.a(string-inst.o):(.text$_ZStplIcSt11char_traitsIcESaIcEENSt7__cxx1112basic_stringIT_T0_T1_EES5_RKS8_[_ZStplIcSt11char_traitsIcESaIcEENSt7__cxx1112basic_stringIT_T0_T1_EES5_RKS8_]+0x0): multiple definition of `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > std::operator+<char, std::char_traits<char>, std::allocator<char> >(char, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
    D:\msys64\tmp\string-e39e30.o:(.text[_ZStplIcSt11char_traitsIcESaIcEENSt7__cxx1112basic_stringIT_T0_T1_EES5_RKS8_]+0x0): first defined here
    clang++.exe: error: linker command failed with exit code 1 (use -v to see invocation)

  2. undefined reference

    std::u16string b;

    This time adding `-static` to clang arguments will cause this error (note: `__imp___cxa_call_unexpected` exists only in dynamic libstdc++):

    D:\msys64\tmp\string-7062fd.o:(.text[_ZNSt7__cxx1112basic_stringIDsSt11char_traitsIDsESaIDsEED2Ev]+0x4a): undefined reference to `__imp___cxa_call_unexpected'
    D:\msys64\tmp\string-7062fd.o:(.text[__clang_call_terminate]+0x7): undefined reference to `__imp___cxa_begin_catch'
    D:\msys64\tmp\string-7062fd.o:(.text[_ZNSt7__cxx1112basic_stringIDsSt11char_traitsIDsESaIDsEE10_M_destroyEy]+0x72): undefined reference to `__imp___cxa_call_unexpected'
    clang++.exe: error: linker command failed with exit code 1 (use -v to see invocation)

It is probably related to the way the symbols are build into static libstdc++ for MinGW.
Let's take a look at weak symbol from different test cases:

  1. MinGW, dynamic libstdc++:
    0000000000000000 I __imp__ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE12_M_constructIPKcEEvT_S8_St20forward_iterator_tag
    0000000000000000 T _ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE12_M_constructIPKcEEvT_S8_St20forward_iterator_tag

  2. MinGW, static libstdc++:
    0000000000000000 p .pdata$_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE12_M_constructIPKcEEvT_S8_St20forward_iterator_tag
    0000000000000000 t .text$_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE12_M_constructIPKcEEvT_S8_St20forward_iterator_tag
    0000000000000000 r .xdata$_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE12_M_constructIPKcEEvT_S8_St20forward_iterator_tag
    0000000000000000 T _ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE12_M_constructIPKcEEvT_S8_St20forward_iterator_tag

  3. Linux, static libstdc++:
    0000000000000000 W _ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE12_M_constructIPKcEEvT_S8_St20forward_iterator_tag

This greatly reduces Clang usefulness on Windows with MinGW.
All responses are welcome.

Best Regards,
Mateusz


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Re: [MinGW] Clang issues with static libstdc++

Brian Cain via cfe-dev
The __imp___cxa_begin_catch error seems related to this code in CodeGenModule::CreateRuntimeFunction:
      if (!Local && getTriple().isOSBinFormatCOFF() &&
          !getCodeGenOpts().LTOVisibilityPublicStd) {
        const FunctionDecl *FD = GetRuntimeFunctionDecl(Context, Name);
        if (!FD || FD->hasAttr<DLLImportAttr>()) {
          F->setDLLStorageClass(llvm::GlobalValue::DLLImportStorageClass);
          F->setLinkage(llvm::GlobalValue::ExternalLinkage);
        }
      }

This code assumes that all compiler-referenced runtime functions on COFF are dllimport, unless we happen to see a prototype for them during compilation that says otherwise. Saleem felt we shouldn't rely on the import thunks that the linker generates when you reference an imported function but forget to declare it as dllimport during compilation. It has some performance benefits, but it never really bothered me. Most users don't complain about the extra absolute branch imposed by the PLT on ELF, and those that do are getting -fno-plt soon.

Anyway, you can see the code difference easily here:

$ cat t.cpp
void g();
void f() {
  try {
    g();
  } catch (...) {
  }
}

$ clang -O1 -S t.cpp --target=x86_64-windows-gnu -o - | grep __cxa
        callq   *__imp___cxa_begin_catch(%rip)
        rex64 jmpq      *__imp___cxa_end_catch(%rip) # TAILCALL

$ gcc -O1 -S t.cpp -o - | grep __cxa
        call    __cxa_begin_catch
        call    __cxa_end_catch
        .def    __cxa_begin_catch;      .scl    2;      .type   32;     .endef
        .def    __cxa_end_catch;        .scl    2;      .type   32;     .endef

The other error looks like some kind of COMDAT disagreement between GCC and Clang that will require further investigation. It might relate to our choice to stop using ".text$function_name" for the section.

On Mon, Apr 17, 2017 at 11:06 AM, Mateusz Mikuła via cfe-dev <[hidden email]> wrote:

Clang doesn't work very well with static libstdc++ build for MinGW resulting in "multiple definition ..." or "undefined reference" to the symbols.

Let's consider following code (removed includes and main for readability):

  1. multiple definition:

    std::string a = "a";
    std::string b = '@' + a;

    This simple code build with `-static` flag will cause this error:

    D:\msys64\mingw64\lib\gcc\x86_64-w64-mingw32\6.3.0\libstdc++.a(string-inst.o):(.text$_ZStplIcSt11char_traitsIcESaIcEENSt7__cxx1112basic_stringIT_T0_T1_EES5_RKS8_[_ZStplIcSt11char_traitsIcESaIcEENSt7__cxx1112basic_stringIT_T0_T1_EES5_RKS8_]+0x0): multiple definition of `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > std::operator+<char, std::char_traits<char>, std::allocator<char> >(char, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
    D:\msys64\tmp\string-e39e30.o:(.text[_ZStplIcSt11char_traitsIcESaIcEENSt7__cxx1112basic_stringIT_T0_T1_EES5_RKS8_]+0x0): first defined here
    clang++.exe: error: linker command failed with exit code 1 (use -v to see invocation)

  2. undefined reference

    std::u16string b;

    This time adding `-static` to clang arguments will cause this error (note: `__imp___cxa_call_unexpected` exists only in dynamic libstdc++):

    D:\msys64\tmp\string-7062fd.o:(.text[_ZNSt7__cxx1112basic_stringIDsSt11char_traitsIDsESaIDsEED2Ev]+0x4a): undefined reference to `__imp___cxa_call_unexpected'
    D:\msys64\tmp\string-7062fd.o:(.text[__clang_call_terminate]+0x7): undefined reference to `__imp___cxa_begin_catch'
    D:\msys64\tmp\string-7062fd.o:(.text[_ZNSt7__cxx1112basic_stringIDsSt11char_traitsIDsESaIDsEE10_M_destroyEy]+0x72): undefined reference to `__imp___cxa_call_unexpected'
    clang++.exe: error: linker command failed with exit code 1 (use -v to see invocation)

It is probably related to the way the symbols are build into static libstdc++ for MinGW.
Let's take a look at weak symbol from different test cases:

  1. MinGW, dynamic libstdc++:
    0000000000000000 I __imp__ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE12_M_constructIPKcEEvT_S8_St20forward_iterator_tag
    0000000000000000 T _ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE12_M_constructIPKcEEvT_S8_St20forward_iterator_tag

  2. MinGW, static libstdc++:
    0000000000000000 p .pdata$_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE12_M_constructIPKcEEvT_S8_St20forward_iterator_tag
    0000000000000000 t .text$_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE12_M_constructIPKcEEvT_S8_St20forward_iterator_tag
    0000000000000000 r .xdata$_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE12_M_constructIPKcEEvT_S8_St20forward_iterator_tag
    0000000000000000 T _ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE12_M_constructIPKcEEvT_S8_St20forward_iterator_tag

  3. Linux, static libstdc++:
    0000000000000000 W _ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE12_M_constructIPKcEEvT_S8_St20forward_iterator_tag

This greatly reduces Clang usefulness on Windows with MinGW.
All responses are welcome.

Best Regards,
Mateusz


_______________________________________________
cfe-dev mailing list
[hidden email]
http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev



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[hidden email]
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