[commit] Move zero PC check to frame.c; Was: [RFC] Infinite backtraces...

[Andrew Cagney <cagney@gnu.org>]

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Randolph Chung wrote:
>>I had the same analysis that it should never happen. If Andrew agrees,
>>I would recommend simply putting an assertion instead. Putting a dummy
>>value is not that satisfactory, as you don't know what this is going
>>to be used for.
> 
> 
> i've committed the following
> 
> 2004-12-05  Randolph Chung  <tausq@debian.org>
> 
> 	* hppa-tdep.c (hppa_stub_Frame_unwind_cache): Stop unwinding if 
> 	unwinding from a frame with pc == 0.
> 	(hppa_stub_frame_this_id): Likewise.
> 	(hppa_stub_frame_prev_register): Only provide real values if the frame
> 	cache is not NULL.

FYI,

> Index: hppa-tdep.c
> ===================================================================
> RCS file: /cvs/src/src/gdb/hppa-tdep.c,v
> retrieving revision 1.185
> diff -u -p -r1.185 hppa-tdep.c
> --- hppa-tdep.c	6 Dec 2004 03:32:26 -0000	1.185
> +++ hppa-tdep.c	8 Dec 2004 01:41:08 -0000
> @@ -2111,17 +2124,21 @@ hppa_stub_frame_unwind_cache (struct fra
>    struct gdbarch *gdbarch = get_frame_arch (next_frame);
>    struct hppa_stub_unwind_cache *info;
>    struct unwind_table_entry *u;
>  
>    if (*this_cache)
>      return *this_cache;
>  
> +  if (frame_pc_unwind (next_frame) == 0)
> +    return NULL;
> +

I've checked in the attached.  This test is generic so might as well 
live in frame.c (you'll note that I've made the conditions on which it 
triggers more robust).

committed,
Andrew


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2004-12-12  Andrew Cagney  <cagney@gnu.org>

	* frame.c (get_prev_frame): When unwinding normal frames, check
	that the PC isn't zero.
	* hppa-tdep.c (hppa_stub_frame_unwind_cache): Delete check for a
	zero PC.

Index: frame.c
===================================================================
RCS file: /cvs/src/src/gdb/frame.c,v
retrieving revision 1.196
diff -p -u -r1.196 frame.c
--- frame.c	8 Dec 2004 01:56:16 -0000	1.196
+++ frame.c	12 Dec 2004 16:23:55 -0000
@@ -1257,6 +1257,18 @@ get_prev_frame (struct frame_info *this_
       return NULL;
     }
 
+  /* Assume that the only way to get a zero PC is through something
+     like a SIGSEGV or a dummy frame, and hence that NORMAL frames
+     will never unwind a zero PC.  */
+  if (this_frame->level > 0
+      && get_frame_type (this_frame) == NORMAL_FRAME
+      && get_frame_type (get_next_frame (this_frame)) == NORMAL_FRAME
+      && get_frame_pc (this_frame) == 0)
+    {
+      frame_debug_got_null_frame (gdb_stdlog, this_frame, "zero PC");
+      return NULL;
+    }
+
   return get_prev_frame_1 (this_frame);
 }
 
Index: hppa-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/hppa-tdep.c,v
retrieving revision 1.189
diff -p -u -r1.189 hppa-tdep.c
--- hppa-tdep.c	8 Dec 2004 06:12:40 -0000	1.189
+++ hppa-tdep.c	12 Dec 2004 16:23:57 -0000
@@ -2105,9 +2105,6 @@ hppa_stub_frame_unwind_cache (struct fra
   if (*this_cache)
     return *this_cache;
 
-  if (frame_pc_unwind (next_frame) == 0)
-    return NULL;
-
   info = FRAME_OBSTACK_ZALLOC (struct hppa_stub_unwind_cache);
   *this_cache = info;
   info->saved_regs = trad_frame_alloc_saved_regs (next_frame);