gdbtk: Patch for terrible slow stepping

[Roland Schwingel <Roland dot Schwingel at onevision dot de>]

Hi....

I today found this mailing list... I found a bug in gdbtk which made it 
terribly slow using it (especially when running on cygwin).
I posted this problem 2 days ago to the gdb mailing list. Yesterday I 
was able to fix this problem in my own.

For details to the problem please look here:
http://sources.redhat.com/ml/gdb/2003-05/msg00298.html

I made a patch to gdb/gdbtk/generic/gdbtk-cmds.c (based on current GDB 
current CVS head) which I want to supply here
now. Maybe someone can check this in, after validation?
(Btw. the fix description I posted to standard gdb mailinglist yesterday 
was slightly incorrect - sorry, due to technical problems I couldn't
supply a diff yesterday. The fix here is totally correct - from my point 
of view ;-)

This fix bypasses unneeded calls to lookup_symtab() which appears to be 
evil slow, at least in many cases.

Thanks,

Roland

--- gdbtk-cmds.c	2003-05-23 09:02:15.000000000 +0200
+++ gdbtk-cmds.c.patched	2003-05-23 11:22:29.000000000 +0200
@@ -35,6 +35,7 @@
 #include "top.h"
 #include "annotate.h"
 #include "block.h"
+#include "filenames.h"
 
 /* tcl header files includes varargs.h unless HAS_STDARG is defined,
    but gdb uses stdarg.h, so make sure HAS_STDARG is defined.  */
@@ -1036,7 +1037,7 @@
 		       int objc, Tcl_Obj *CONST objv[])
 {
   struct symtab *st;
-  char *filename, *fullname;
+  char *filename, *fullname = NULL;
 
   if (objc != 2)
     {
@@ -1045,20 +1046,36 @@
     }
 
   filename = Tcl_GetStringFromObj (objv[1], NULL);
-  st = lookup_symtab (filename);
+  
+  if (IS_ABSOLUTE_PATH (filename))
+  {
+  	 struct stat st;
+  	 const int status = stat (filename, &st);
 
-  /* We should always get a symtab. */
-  if (!st)
+	 if (status == 0)
+	 {
+  		if (S_ISREG (st.st_mode))
+  			fullname = filename;
+	 }
+  }
+  
+  if (fullname == NULL)
+  {
+  	st = lookup_symtab (filename);
+
+  	/* We should always get a symtab. */
+  	if (!st)
     {
       gdbtk_set_result (interp, "File not found in symtab (2)");
       return TCL_ERROR;
     }
 
-  if (st->fullname == NULL)
+  	if (st->fullname == NULL)
     fullname = symtab_to_filename (st);
-  else
+  	else
     fullname = st->fullname;
-
+  }
+  
   /* We may not be able to open the file (not available). */
   if (fullname == NULL)
     {