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Date: Wed, 20 Jun 2007 12:46:34 -0400
From: "Larry Hall (Cygwin)" <reply-to-list-only-lh AT cygwin DOT com>
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To: cygwin AT cygwin DOT com
Subject: Re: shared library - undefined symbols
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Dan O'Brien wrote:
> I'm porting a C++ application that builds and runs on linux.  This application allows for "plugins" and will dynamically load any shared object found in its plugin directory.  This works fine on linux.  The trouble I'm having is getting the plugin "shared library" are in to build.  I'm running into undefined references (which should be allowed because they will be resolved when the shared library is loaded -- these symbols exist in the main application).
> 
> The failing g++ line:
> 
> g++ -o build/unknown-pc-cygwin/debug/plugin.so -shared -Wl,--allow-shlib-undefined build/unknown-pc-cygwin/debug/.objs/plugin.o build/unknown-pc-cygwin/debug/.objs/NullFilter.o build/unknown-pc-cygwin/debug/.objs/NullFilterFactory.o
> 
> The failing output:
> 
> build/unknown-pc-cygwin/debug/.objs/NullFilter.o: In function `_ZN10NullFilter7processERSt4listI14MatchingPeriodSaIS1_EE':
> /home/OBrienDM/gpm/src/NullFilter.cpp:32: undefined reference to `getLoggerVerbosity()'
> /home/OBrienDM/gpm/src/NullFilter.cpp:32: undefined reference to `isLoggerEnabledFor(int)'
> /home/OBrienDM/gpm/src/NullFilter.cpp:32: undefined reference to `TimeStamp::TimeStamp()'
> /home/OBrienDM/gpm/src/NullFilter.cpp:32: undefined reference to `operator<<(std::basic_ostream<char, std::char_traits<char> >&, TimeStamp const&)'
> /home/OBrienDM/gpm/src/NullFilter.cpp:32: undefined reference to `TimeStamp::~TimeStamp()'
> build/unknown-pc-cygwin/debug/.objs/NullFilter.o: In function `_ZN10NullFilter7processERSt4listI14MatchingPeriodSaIS1_EE':
> /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/sstream:511: undefined reference to `log(int, std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, char const*, unsigned int)'
> build/unknown-pc-cygwin/debug/.objs/NullFilter.o: In function `_ZN10NullFilter7processERSt4listI14MatchingPeriodSaIS1_EE':
> /home/OBrienDM/gpm/src/NullFilter.cpp:32: undefined reference to `TimeStamp::~TimeStamp()'
> build/unknown-pc-cygwin/debug/.objs/NullFilterFactory.o: In function `_ZN17NullFilterFactoryC1Ev':
> /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/ext/new_allocator.h:62: undefined reference to `MatcherFactory::instance()'
> /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/ext/new_allocator.h:62: undefined reference to `MatcherFactory::registerFilterFactory(std::basic_string<char, std::char_traits<char>, std::allocator<char> >, FilterFactoryAdapter*)'
> build/unknown-pc-cygwin/debug/.objs/NullFilterFactory.o: In function `_ZN17NullFilterFactoryC2Ev':
> /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/ext/new_allocator.h:62: undefined reference to `MatcherFactory::instance()'
> /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/ext/new_allocator.h:62: undefined reference to `MatcherFactory::registerFilterFactory(std::basic_string<char, std::char_traits<char>, std::allocator<char> >, FilterFactoryAdapter*)'
> collect2: ld returned 1 exit status
> 
> These missing references are found in the executable:
> 
>  nm --demangle  ./build/unknown-pc-cygwin/debug/gpm.exe |grep 'getLoggerVerbosity()'
> 00456820 T getLoggerVerbosity()
>  nm --demangle  ./build/unknown-pc-cygwin/debug/gpm.exe |grep 'TimeStamp::~TimeStamp()'
> 004b4470 T TimeStamp::~TimeStamp()
> 004b4460 T TimeStamp::~TimeStamp()
> 
> And will get resolved at load time.
> 
> The g++ line works fine under linux.
> 
> Any other flags I'm missing?
> 

DLLs are not SOs.  DLLs must resolve all symbols at link time.  That's why
Windows has the concept of export libraries.  See MSDN documentation for
a discussion of this.  So essentially, you'll need to have one or more
export libraries with stubs to the missing symbols in them.  List them
when compiling your plugin.  That will resolve the issue.

-- 
Larry Hall                              http://www.rfk.com
RFK Partners, Inc.                      (508) 893-9779 - RFK Office
216 Dalton Rd.                          (508) 893-9889 - FAX
Holliston, MA 01746

_____________________________________________________________________

A: Yes.
 > Q: Are you sure?
 >> A: Because it reverses the logical flow of conversation.
 >>> Q: Why is top posting annoying in email?

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