[cfe-dev] Linker error and obfuscated name: Part II

Edward Diener eldlistmailingz at tropicsoft.com
Thu Aug 6 13:21:52 PDT 2015


On 8/6/2015 12:44 PM, Reid Kleckner wrote:
> Hm, GCC never tries to import RTTI, so maybe it makes sense that we
> never export it. Anyway, there's a bug here. Maybe David knows what's up.

I tried this simple example:

// ex_aclass.hpp

#ifndef EX_ACLASS_HPP
#define EX_ACLASS_HPP
#if defined(BLD_EX_EXAMPLE)
  	#define EX_DECL __attribute__((__dllexport__))
#else
	#define EX_DECL __attribute__((__dllimport__))
#endif
class EX_DECL ex_aclass
{
public:
     int a_function(long);
};
#endif // EX_ACLASS_HPP

// ex_aclass.cpp

#define BLD_EX_EXAMPLE
#include "ex_aclass.hpp"
int ex_aclass::a_function(long amt)
	{
	return(amt > 1000000 ? 10 : 20);
	}

// Compile ex_aclass

clang++.exe -c -x c++ -D__MINGW_FORCE_SYS_INTRINS -O0 -g -fno-inline 
-Wall -g -march=i686 -m32 -o "ex_aclass.obj" "ex_aclass.cpp"

// Link to ex_ac dll

clang++.exe -o "ex_ac.dll" -Wl,-soname -Wl,ex_ac.dll -shared 
-Wl,--start-group "ex_aclass.obj" -Wl,-Bstatic -Wl,-Bdynamic 
-Wl,--end-group -g -march=i686 -m32

// ex_use_aclass.cpp

#include "ex_aclass.hpp"
int main(int argc,char * argv[])
	{
	ex_aclass aclass;
	int ret(aclass.a_function(10000));
	return ret;
	}

// Compile ex_use_aclass

clang++.exe -c -x c++ -D__MINGW_FORCE_SYS_INTRINS -O0 -g -fno-inline 
-Wall -g -march=i686 -m32 -o "ex_use_aclass.obj" "ex_use_aclass.cpp"

// Link ex_use_ac executable

clang++.exe -Wl,-R -Wl,"." -Wl,-rpath-link -Wl,"." -o "ex_use_ac.exe" 
-Wl,--start-group "ex_use_aclass.obj" "ex_ac.dll" -Wl,-Bstatic 
-Wl,-Bdynamic -Wl,--end-group -g -march=i686 -m32

All of this worked with no problems.

So the basic ability to access functionality in a class in a DLL from 
outside that DLL works fine using clang on Windows. It is something 
specific in my original example below that is causing linking problems, 
whether I export entire classes or whether I export individual member 
functions. Just thought I would let you know. Needless to say I need to 
solve my original problem because that code mimics the design of a very 
small portion of the Boost serialization library and is the cause why 
the Boost serialization library will not build with clang on Windows 
targeting gcc.

>
> On Thu, Aug 6, 2015 at 9:36 AM, Reid Kleckner
> <rnk-hpIqsD4AKlfQT0dZR+AlfA at public.gmane.org
> <mailto:rnk-hpIqsD4AKlfQT0dZR+AlfA at public.gmane.org>> wrote:
>
>     I reproduced your example, and it looks like we are forgetting to
>     export RTTI with dllexport in Itanium. We only export the vtable.
>     This is what each compiler exports for ex_xml_exception.obj:
>
>     $ dumpbin -directives ex_xml_exception.clang.obj | grep -export:_ZT
>     | c++filt --no-strip-underscore
>         -export:virtual thunk to ex_xml_exception::~ex_xml_exception()
>         -export:virtual thunk to ex_xml_exception::~ex_xml_exception()
>         -export:vtable for ex_xml_exception,data
>
>     $ dumpbin -directives ex_xml_exception.gcc.obj | grep -export:_ZT |
>     c++filt --no-strip-underscore
>         -export:typeinfo for ex_exception,data
>         -export:typeinfo for ex_xml_exception,data
>         -export:construction vtable for
>     ex_exception-in-ex_xml_exception,data
>         -export:VTT for ex_xml_exception,data
>         -export:vtable for ex_xml_exception,data
>         -export:virtual thunk to ex_xml_exception::~ex_xml_exception()
>         -export:virtual thunk to ex_xml_exception::~ex_xml_exception()
>
>     In your previous example where the whole class wasn't exported, I
>     think we might be doing the wrong thing when the key function is
>     dllimport / dllexport. We think that it will provide exported
>     symbols for vtables and RTTI but it doesn't. This is something we
>     didn't run into because the MSVC ABI doesn't have key functions.
>
>     On Thu, Aug 6, 2015 at 6:16 AM, Edward Diener
>     <eldlistmailingz at tropicsoft.com
>     <mailto:eldlistmailingz-5p0dqD/c5LGWd6l5hS35sQ at public.gmane.org>> wrote:
>
>         Using clang on Windows targeting mingw(-64)/gcc since it does
>         not appear possible to export individual member functions of a
>         class, as well as export the RTTI of the class, without
>         exporting the entire class, I have changed my example in my post
>         "Linker error and obfuscated name" to export the entire class
>         itself. But I am still seeing a linker error, Here is the
>         changed code and command lines:
>
>         // ex_decl.hpp
>
>         #ifndef EX_DECL_HPP
>         #define EX_DECL_HPP
>         #if defined(BLD_EX_EXAMPLE)
>              #define EX_DECL __attribute__((__dllexport__))
>         #else
>              #define EX_DECL __attribute__((__dllimport__))
>         #endif
>         #endif // EX_DECL_HPP
>
>         // ex_exception.hpp
>
>         #ifndef EX_EXCEPTION_HPP
>         #define EX_EXCEPTION_HPP
>         #include <exception>
>         #include "ex_decl.hpp"
>         class EX_DECL ex_exception :
>              public virtual std::exception
>         {
>         private:
>              char m_buffer[128];
>         protected:
>              unsigned int append(unsigned int l, const char * a);
>              ex_exception() ;
>         public:
>              typedef enum {
>                no_exception,
>                other_exception
>              } ex_exception_code;
>              ex_exception_code code;
>              ex_exception(ex_exception_code c,const char * e1 = 0,const
>         char * e2 = 0) ;
>              ex_exception(ex_exception const &) ;
>              virtual ~ex_exception() throw() ;
>              virtual const char * what() const throw() ;
>         };
>         #endif // EX_EXCEPTION_HPP
>
>         // ex_exception.cpp
>
>         #include <exception>
>         #include <cstring>
>         #define BLD_EX_EXAMPLE
>         #include "ex_exception.hpp"
>         unsigned int ex_exception::append(unsigned int l, const char * a){
>              while(l < (sizeof(m_buffer) - 1)){
>                  char c = *a++;
>                  if('\0' == c)
>                      break;
>                  m_buffer[l++] = c;
>              }
>              m_buffer[l] = '\0';
>              return l;
>         }
>         ex_exception::ex_exception(ex_exception_code c,const char *
>         e1,const char * e2) : code(c)
>         {
>            unsigned int length = 0;
>              switch(code){
>              case no_exception:
>                  length = append(length, "uninitialized exception");
>                  break;
>              case other_exception:
>                  length = append(length, "unknown derived exception");
>                  break;
>              default:
>                  length = append(length, "programming error");
>                  break;
>              }
>         }
>         ex_exception::ex_exception(ex_exception const & oth) :
>         std::exception(oth),code(oth.code)
>         {
>              std::memcpy(m_buffer,oth.m_buffer,sizeof m_buffer);
>         }
>         ex_exception::~ex_exception() throw() {}
>         const char * ex_exception::what() const throw() { return
>         m_buffer; }
>         ex_exception::ex_exception() : code(no_exception) {}
>
>         // Compile ex_exception.cpp
>
>         clang++.exe -c -x c++ -D__MINGW_FORCE_SYS_INTRINS
>         -Wno-unused-local-typedef -Wno-dll-attribute-on-redeclaration
>         -O0 -g -fno-inline -Wall -g -march=i686 -m32 -o
>         "ex_exception.obj" "ex_exception.cpp"
>
>         // ex_xml_exception.hpp
>
>         #ifndef EX_XML_EXCEPTION_HPP
>         #define EX_XML_EXCEPTION_HPP
>         #include <exception>
>         #include "ex_decl.hpp"
>         #include "ex_exception.hpp"
>         class EX_DECL ex_xml_exception :
>              public virtual ex_exception
>         {
>         public:
>              typedef enum {
>                  xml_archive_parsing_error,
>                  xml_archive_tag_mismatch,
>                  xml_archive_tag_name_error
>              } ex_exception_code;
>              ex_xml_exception(ex_exception_code c,const char * e1 =
>         0,const char * e2 = 0);
>              ex_xml_exception(ex_xml_exception const &) ;
>              virtual ~ex_xml_exception() throw() ;
>         };
>         #endif // EX_XML_EXCEPTION_HPP
>
>         // ex_xml_exception.cpp
>
>         #include <exception>
>         #define BLD_EX_EXAMPLE
>         #include "ex_xml_exception.hpp"
>         ex_xml_exception::ex_xml_exception(ex_exception_code c,const
>         char * e1,const char * e2) :
>                  ex_exception(other_exception, e1, e2)
>              {
>                  switch(c){
>                  case xml_archive_parsing_error:
>                      ex_exception::append(0, "unrecognized XML syntax");
>                      break;
>                  case xml_archive_tag_mismatch:
>                      ex_exception::append(0, "XML start/end tag mismatch");
>                      if(0 != e1){
>                          ex_exception::append(0, " - ");
>                          ex_exception::append(0, e1);
>                      }
>                      break;
>                  case xml_archive_tag_name_error:
>                      ex_exception::append(0, "Invalid XML tag name");
>                      break;
>                  default:
>                      ex_exception::append(0, "programming error");
>                      break;
>                  }
>              }
>         ex_xml_exception::ex_xml_exception(ex_xml_exception const & oth)
>         : std::exception(oth),ex_exception(oth){}
>         ex_xml_exception::~ex_xml_exception() throw() {}
>
>         // Compile ex_xml_exception.cpp
>
>         clang++.exe -c -x c++ -D__MINGW_FORCE_SYS_INTRINS
>         -Wno-unused-local-typedef -Wno-dll-attribute-on-redeclaration
>         -O0 -g -fno-inline -Wall -g -march=i686 -m32 -o
>         "ex_xml_exception.obj" "ex_xml_exception.cpp"
>
>         // Link exmp-clang37-d-1_59.dll
>
>         clang++.exe -o "exmp-clang37-d-1_59.dll" -Wl,-soname
>         -Wl,exmp-clang37-d-1_59.dll -shared -Wl,--start-group
>         "ex_exception.obj" "ex_xml_exception.obj"  -Wl,-Bstatic
>         -Wl,-Bdynamic  -Wl,--end-group -g -march=i686 -m32
>
>         // throw_exception_ex.cpp
>
>         #include "ex_xml_exception.hpp"
>         template<class E> void throw_exception(E const & e) { throw e; }
>         int main(int argc,char * argv[])
>         {
>              if (argc > 1)
>                    {
>
>         throw_exception(ex_xml_exception(ex_xml_exception::xml_archive_parsing_error));
>
>                    }
>              return 0;
>         }
>
>         // Compile throw_exception_ex.cpp
>
>         clang++.exe -c -x c++ -D__MINGW_FORCE_SYS_INTRINS
>         -Wno-unused-local-typedef -Wno-dll-attribute-on-redeclaration
>         -O0 -g -fno-inline -Wall -g -march=i686 -m32 -o
>         "throw_exception_ex.obj" "throw_exception_ex.cpp"
>
>         // Link thr_exmp.exe
>
>         clang++.exe -Wl,-R -Wl,"." -Wl,-rpath-link -Wl,"." -o
>         "thr_exmp.exe" -Wl,--start-group "throw_exception_ex.obj"
>         "exmp-clang37-d-1_59.dll" -Wl,-Bstatic -Wl,-Bdynamic
>         -Wl,--end-group -g -march=i686 -m32
>
>         // Error message from this link
>
>         throw_exception_ex.obj: In function
>         `Z15throw_exceptionI16ex_xml_exceptionEvRKT_':
>         throw_exception_ex.cpp:2: undefined reference to
>         `_imp___ZTI16ex_xml_exception'
>         clang++.exe: error: linker command failed with exit code 1 (use
>         -v to see invocation)
>
>         So even when I export/import the entire class rather than
>         individual member functions, I can not link my final module
>         successfully as it is still looking for something in the shared
>         library that it says is not there.
>
>         This same code succeeds without problem with mingw(-64)/gcc on
>         Windows.




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