fixes for _XtInherit on cygwin.

1 files changed, 61 insertions, 1 deletions

diff --git a/lib/Xt/Initialize.c b/lib/Xt/Initialize.c
index fa4379987..9ad6522f6 100644
--- a/lib/Xt/Initialize.c
+++ b/lib/Xt/Initialize.c
@@ -32,7 +32,7 @@ OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION  WITH
 THE USE OR PERFORMANCE OF THIS SOFTWARE.
 
 ******************************************************************/
-/* $XFree86: xc/lib/Xt/Initialize.c,v 3.20 2002/04/10 16:20:07 tsi Exp $ */
+/* $XFree86: xc/lib/Xt/Initialize.c,v 3.21 2003/04/21 16:34:27 herrb Exp $ */
 
 /*
 
@@ -184,6 +184,66 @@ void _XtInherit()
 #define _XtInherit __XtInherit
 #endif
 
+
+#if defined(__CYGWIN__)
+/*
+ * The Symbol _XtInherit is used in two different manners.
+ * First it could be used as a generic function and second
+ * as an absolute address reference, which will be used to
+ * check the initialisation process of several other libraries.
+ * Because of this the symbol must be accessable by all
+ * client dll's and applications.  In unix environments
+ * this is no problem, because the used shared libraries
+ * format (elf) supports this immediatly.  Under Windows
+ * this isn't true, because a functions address in a dll
+ * is different from the same function in another dll or
+ * applications, because the used Portable Executable
+ * File adds a code stub to each client to provide the
+ * exported symbol name.  This stub uses an indirect
+ * pointer to get the original symbol address, which is
+ * then jumped to, like in this example: 
+ *
+ * --- client ---                                     --- dll ----
+ *  ... 
+ *  call foo 
+ * 
+ * foo: jmp (*_imp_foo)               ---->           foo: .... 
+ *      nop
+ *      nop       
+ * 
+ * _imp_foo: .long <index of foo in dll export table, is
+ *		    set to the real address by the runtime linker>
+ * 
+ * Now it is clear why the clients symbol foo isn't the same
+ * as in the dll and we can think about how to deal which
+ * this two above mentioned requirements, to export this
+ * symbol to all clients and to allow calling this symbol
+ * as a function.  The solution I've used exports the
+ * symbol _XtInherit as data symbol, because global data
+ * symbols are exported to all clients.  But how to deal
+ * with the second requirement, that this symbol should
+ * be used as function.  The Trick is to build a little
+ * code stub in the data section in the exact manner as
+ * above explained.  This is done with the assembler code 
+ * below.
+ * 
+ * Ralf Habacker
+ *
+ * References: 
+ * msdn          http://msdn.microsoft.com/msdnmag/issues/02/02/PE/PE.asp
+ * cygwin-xfree: http://www.cygwin.com/ml/cygwin-xfree/2003-10/msg00000.html
+ */
+
+asm (".data\n\
+ .globl __XtInherit        \n\
+ __XtInherit:      jmp *_y \n\
+  _y: .long ___XtInherit   \n\
+    .text                 \n"); 
+
+#define _XtInherit __XtInherit
+#endif
+
+
 void _XtInherit()
 {
     XtErrorMsg("invalidProcedure","inheritanceProc",XtCXtToolkitError,