Index: i386-tdep.c
===================================================================
RCS file: /gnat.dev/cvs/Dev/gdb/gdb-6.4/gdb/i386-tdep.c,v
retrieving revision 1.4
retrieving revision 1.5
diff -u -p -r1.4 -r1.5
--- i386-tdep.c	10 Aug 2006 22:18:30 -0000	1.4
+++ i386-tdep.c	22 Aug 2006 21:45:53 -0000	1.5
@@ -1029,6 +1029,41 @@ i386_frameless_adjust_cache_hack (struct
     }
 }
 
+/* Return non-zero if the function starting at START_PC has a prologue
+   that sets up a standard frame.  */
+
+static int
+i386_function_has_frame (CORE_ADDR start_pc)
+{
+  struct i386_frame_cache cache;
+
+  cache.locals = -1;
+  i386_analyze_prologue (start_pc, 0xffffffff, &cache);
+
+  return (cache.locals >= 0);
+}
+
+/* Return non-zero if PC is inside one of the inferior's DLLs.  */
+
+static int
+i386_in_dll (CORE_ADDR pc)
+{
+   char *so_name = solib_address (pc);
+   int len;
+
+   if (so_name == NULL)
+     return 0;
+
+   len = strlen (so_name);
+   if (len < 5)
+     return 0;
+
+   return ((so_name[len - 1] == 'l' || so_name[len - 1] == 'L')
+           && (so_name[len - 2] == 'l' || so_name[len - 2] == 'L')
+           && (so_name[len - 3] == 'd' || so_name[len - 3] == 'D')
+           && so_name[len - 4] == '.');
+}
+
 /* Normal frames.  */
 
 static struct i386_frame_cache *
@@ -1075,10 +1110,38 @@ i386_frame_cache (struct frame_info *nex
 	 frame by looking at the stack pointer.  For truly "frameless"
 	 functions this might work too.  */
 
-      i386_frameless_adjust_cache_hack (cache, frame_pc_unwind (next_frame));
+      if (i386_in_dll (cache->pc)
+          && !i386_function_has_frame (cache->pc))
+        {
+          /* Functions in DLL for which do not seem to create a standard
+             frame are unwound using %ebp.  This is actually the caller's
+             frame base instead of our own, but there are some functions
+             such as WaitForSingleObjectEx in one of the Windows system
+             DLLs for which the frame base cannot possibly be determined
+             from the stack pointer.  As a consequence, our caller will be
+             missing from the backtrace, but this is better than having
+             an aborted backtrace due to a bogus frame base.
+             
+             We use this approach only for functions in DLLs because
+             this is the only place where we have seen the type of
+             highly optimized code that cause us trouble.  In other
+             cases, we expect the code to come with frame debugging
+             information, making prologue scanning unnecessary.
+             
+             We also avoid blindly following %ebp if we are midway through
+             setting up a standard frame.  In that case, we know how to
+             determine the frame base using the stack pointer.  */
 
-      frame_unwind_register (next_frame, I386_ESP_REGNUM, buf);
-      cache->base = extract_unsigned_integer (buf, 4) + cache->sp_offset;
+          cache->saved_regs[I386_EBP_REGNUM] = 0;
+        }
+      else
+        {
+          i386_frameless_adjust_cache_hack (cache,
+                                            frame_pc_unwind (next_frame));
+ 
+          frame_unwind_register (next_frame, I386_ESP_REGNUM, buf);
+          cache->base = extract_unsigned_integer (buf, 4) + cache->sp_offset;
+        }
     }
 
   /* Now that we have the base address for the stack frame we can