[RFC] Unexpected automatic language switch - get_frame_language()

Joel Brobecker brobecker@gnat.com
Wed Dec 10 17:42:00 GMT 2003


> >2003-12-09  J. Brobecker  <brobecker@gnat.com>
> >
> >        * frame.c (select_frame): Get the current frame PC using
> >        get_frame_address_in_block() instead of get_frame_pc().
> >        * stack.c (get_frame_language): Likewise.
> >
> >Tested on x86-linux, with no regression.
> >
> >OK to apply?
> 
> Yes, but just add a comment at each point reminding us why the PC is 
> wrong before committing.

Thanks. Here is the patch that I ended up committing. Let me know if
somebody would like the comments to be worded differently.

-- 
Joel
-------------- next part --------------
Index: frame.c
===================================================================
RCS file: /cvs/src/src/gdb/frame.c,v
retrieving revision 1.152
diff -u -p -r1.152 frame.c
--- frame.c	23 Nov 2003 21:49:12 -0000	1.152
+++ frame.c	10 Dec 2003 17:21:46 -0000
@@ -917,7 +917,13 @@ select_frame (struct frame_info *fi)
      source language of this frame, and switch to it if desired.  */
   if (fi)
     {
-      s = find_pc_symtab (get_frame_pc (fi));
+      /* We retrieve the frame's symtab by using the frame PC.  However
+         we cannot use the frame pc as is, because it usually points to
+         the instruction following the "call", which is sometimes the
+         first instruction of another function.  So we rely on
+         get_frame_address_in_block() which provides us with a PC which
+         is guaranteed to be inside the frame's code block.  */
+      s = find_pc_symtab (get_frame_address_in_block (fi));
       if (s
 	  && s->language != current_language->la_language
 	  && s->language != language_unknown
Index: stack.c
===================================================================
RCS file: /cvs/src/src/gdb/stack.c,v
retrieving revision 1.97
diff -u -p -r1.97 stack.c
--- stack.c	23 Nov 2003 20:41:17 -0000	1.97
+++ stack.c	10 Dec 2003 17:21:47 -0000
@@ -2036,7 +2036,14 @@ get_frame_language (void)
 
   if (deprecated_selected_frame)
     {
-      s = find_pc_symtab (get_frame_pc (deprecated_selected_frame));
+      /* We determine the current frame language by looking up its
+         associated symtab.  To retrieve this symtab, we use the frame PC.
+         However we cannot use the frame pc as is, because it usually points
+         to the instruction following the "call", which is sometimes the first
+         instruction of another function.  So we rely on
+         get_frame_address_in_block(), it provides us with a PC which is
+         guaranteed to be inside the frame's code block.  */
+      s = find_pc_symtab (get_frame_address_in_block (deprecated_selected_frame));
       if (s)
 	flang = s->language;
       else


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