[commit] Fix backtrace past "clone" on powerpc

["Ulrich Weigand" <uweigand@de.ibm.com>]

Hello,

backtrace in multi-threaded applications would tend to throw an error:

where^M
#0  0x0fcfdb34 in sem_wait@GLIBC_2.0 () from /lib/libpthread.so.0^M
#1  0x100008f0 in spin (vp=0x0) at /home/uweigand/fsf/gdb-head/gdb/testsuite/gdb.threads/tls.c:97^M
#2  0x0fcf6764 in start_thread () from /lib/libpthread.so.0^M
#3  0x0ff2c604 in clone () from /lib/libc.so.6^M
Backtrace stopped: previous frame inner to this frame (corrupt stack?)^M

because clone was not recognized to terminate the stack.

The patch below fixes this by having rs6000_frame_this_id return the null
frame ID in that case (just like many other targets do already).

Tested on powerpc-linux and powerpc64-linux; committed to mainline.

Bye,
Ulrich


ChangeLog:

	* rs6000-tdep.c (rs6000_frame_this_id): If info->base is 0,
	return the null frame ID to terminate the backtrace.

diff -urNp gdb-orig/gdb/rs6000-tdep.c gdb-head/gdb/rs6000-tdep.c
--- gdb-orig/gdb/rs6000-tdep.c	2008-05-04 02:07:36.026688000 +0200
+++ gdb-head/gdb/rs6000-tdep.c	2008-05-04 02:08:56.461342375 +0200
@@ -2550,6 +2550,10 @@ rs6000_frame_this_id (struct frame_info 
 {
   struct rs6000_frame_cache *info = rs6000_frame_cache (this_frame,
 							this_cache);
+  /* This marks the outermost frame.  */
+  if (info->base == 0)
+    return;
+
   (*this_id) = frame_id_build (info->base, get_frame_func (this_frame));
 }
 
-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com