[cfe-dev] Linker error and obfuscated name: Part II
David Majnemer
david.majnemer at gmail.com
Thu Aug 6 13:58:37 PDT 2015
On Thu, Aug 6, 2015 at 1:21 PM, Edward Diener <
eldlistmailingz at tropicsoft.com> wrote:
> 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.
>
Should be fixed in r244266.
>
>
>> 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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