RFA: Fix check for no-saved-pc

[Michael Snyder <msnyder at specifix dot com>]

There's a check in get_prev_frame to see if the next saved pc
is zero.  I think it has an off-by-one error, and is checking 
for the pc of the wrong frame.

To test this, I took the corefile that's generated by the
testsuite (gdb.base/corefile.exp), edited it with khexedit, 
and nulled out one of the saved return addresses on the stack.

This is the gdb output before my change:

Core was generated by `gdb/testsuite/gdb.base/coremaker'.
Program terminated with signal 6, Aborted.
#0  0x40000402 in __kernel_vsyscall ()
(gdb) bt
#0  0x40000402 in __kernel_vsyscall ()
#1  0x00a7bfa0 in raise () from /lib/libc.so.6
#2  0x00a7d8b1 in abort () from /lib/libc.so.6
#3  0x080486ce in func2 () at gdb/testsuite/gdb.base/coremaker.c:127
#4  0x080486d9 in func1 () at gdb/testsuite/gdb.base/coremaker.c:133
#5  0x00000000 in ?? ()
(gdb) 

And this is the output with the attached patch:

(gdb) bt
#0  0x40000402 in __kernel_vsyscall ()
#1  0x00a7bfa0 in raise () from /lib/libc.so.6
#2  0x00a7d8b1 in abort () from /lib/libc.so.6
#3  0x080486ce in func2 () at gdb/testsuite/gdb.base/coremaker.c:127
#4  0x080486d9 in func1 () at gdb/testsuite/gdb.base/coremaker.c:133
Backtrace stopped: frame did not save the PC
(gdb) 

No other test suite changes, tests run on native i386 linux.


2007-11-30  Michael Snyder  <msnyder@specifix.com>

	* frame.c (get_prev_frame): Remove unused local variable.
	(get_prev_frame): Check for null saved pc in the following
	("prev") frame, not the current (already valid) frame.
	Set up stop_reason conditions for printing stop reason.

Index: frame.c
===================================================================
RCS file: /cvs/src/src/gdb/frame.c,v
retrieving revision 1.235
diff -u -p -r1.235 frame.c
--- frame.c	2 Nov 2007 14:47:27 -0000	1.235
+++ frame.c	30 Nov 2007 22:48:47 -0000
@@ -1355,8 +1355,6 @@ inside_entry_func (struct frame_info *th
 struct frame_info *
 get_prev_frame (struct frame_info *this_frame)
 {
-  struct frame_info *prev_frame;
-
   /* Return the inner-most frame, when the caller passes in NULL.  */
   /* NOTE: cagney/2002-11-09: Not sure how this would happen.  The
      caller should have previously obtained a valid frame using
@@ -1469,9 +1467,12 @@ get_prev_frame (struct frame_info *this_
   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_pc_unwind (this_frame) == 0)
     {
       frame_debug_got_null_frame (gdb_stdlog, this_frame, "zero PC");
+      this_frame->stop_reason = UNWIND_NO_SAVED_PC;
+      this_frame->prev_p = 1;
+      this_frame->prev = NULL;
       return NULL;
     }