mingw/libxml2 issue

问题:

I'm trying to use libxml2 (v2.2.6.0) with mingw under win7 I added the lib -llibmlx2, but each time I compile I get :

error: undefined reference to `imp_xmlFree'

On Google I found this: http://osdir.com/ml/gnome.lib.xml.ge.../msg00003.html
But still doesn't work.

Any idea ?

thanks...

回答1:

I believe that this problem only happens when using precompiled libxml2 binaries prepared by Igor Zlatovic. I suspect that the problem goes away if using libxml2 lib natively compiled with mingw.

Here is the declaration of xmlFree in libxml/globals.h:

#else /* !LIBXML_THREAD_ALLOC_ENABLED */ XMLPUBVAR xmlMallocFunc xmlMalloc; XMLPUBVAR xmlMallocFunc xmlMallocAtomic; XMLPUBVAR xmlReallocFunc xmlRealloc; XMLPUBVAR xmlFreeFunc xmlFree; XMLPUBVAR xmlStrdupFunc xmlMemStrdup; #endif /* LIBXML_THREAD_ALLOC_ENABLED */ 

and XMLPUBVAR is expanded by

#define XMLPUBVAR __declspec(dllimport) extern 

from libxml/xmlexports.h

First observation. xmlFree is not a function but a variable. This is an exceptional occurrence as almost all the other libxml2 functions are real exported functions. This explain why xmlFree() is the only problematic function encountered by people.

mingw compiler change the imported symbol name from xmlFree to _imp__xmlFree which is not found in libxml2.lib. I am guessing that with other compilers such as MSVC, the linker is instead searching for the correct symbol _xmlFree found inside libxml2.lib:

C:\MinGW\msys\1.0\home\100517891\embedded\ext\libxml2\lib>"c:\Program Files\Microsoft Visual Studio 9.0\VC\bin\dumpbin.exe" /exports libxml2.lib | grep xmlFree               _xmlFree               _xmlFreeAttributeTable               _xmlFreeAutomata               _xmlFreeCatalog               _xmlFreeDoc               _xmlFreeDocElementContent               _xmlFreeDtd               _xmlFreeElementContent               _xmlFreeElementTable               _xmlFreeEntitiesTable               _xmlFreeEnumeration               _xmlFreeIDTable               _xmlFreeInputStream               _xmlFreeMutex               _xmlFreeNode               _xmlFreeNodeList               _xmlFreeNotationTable               _xmlFreeNs               _xmlFreeNsList               _xmlFreeParserCtxt               _xmlFreeParserInputBuffer               _xmlFreePattern               _xmlFreePatternList               _xmlFreeProp               _xmlFreePropList               _xmlFreeRMutex               _xmlFreeRefTable               _xmlFreeStreamCtxt               _xmlFreeTextReader               _xmlFreeTextWriter               _xmlFreeURI               _xmlFreeValidCtxt 

I have not found any way to fix the linkage error but a simple and safe way to workaround the problem is to acknowledge the fact that xmlFree is a simple function pointer variable initialized to the address of the standard free() function in globals.c and the only way to change that assignation is to recompile the dll with some debug switches.

Feel free to replace calls to xmlFree() with calls to free(). Everything should be fine and the linkage error will go away.

回答2:

This can be fixed by using the "--disable-shared" flag to configure, e.g.:

./configure --prefix=/mingw --disable-shared

回答3:

You've probably long since fixed this but just in case, try it with -lxml2. That is drop the lib prefix from the library name. You might also need to use the -L option to set the search path. Specify -L before -l on the command line.

回答4:

Try adding -DIN_LIBXML to your compile flags (from related issue).

文章来源: mingw/libxml2 issue