[patch] Fix segfault on a failed watchpoint update

[Jan Kratochvil <jan dot kratochvil at redhat dot com>]

Hi,

currently GDB HEAD segfaults during one case for the PIE inferiors (failing as
it is the unpatched CVS HEAD), segfault fix attached.


Regards,
Jan


crash reproducibility:

$ runtest --target_board=unix/-fPIE/-pie gdb.base/watchpoint.exp
WARNING: Couldn't find the global config file.
Test Run By jkratoch on Sun Mar  2 09:31:14 2008
Native configuration is x86_64-unknown-linux-gnu

                === gdb tests ===

Schedule of variations:
    unix/-fPIE/-pie

Running target unix/-fPIE/-pie
Using /usr/share/dejagnu/baseboards/unix.exp as board description file for target.
Using /usr/share/dejagnu/config/unix.exp as generic interface file for target.
Using ../.././gdb/testsuite/config/unix.exp as tool-and-target-specific interface file.
Running ../.././gdb/testsuite/gdb.base/watchpoint.exp ...
FAIL: gdb.base/watchpoint.exp: run to marker1 in test_simple_watchpoint
ERROR: Process no longer exists
ERROR: Couldn't send disable 3 to GDB.
ERROR: Delete all breakpoints in delete_breakpoints (timeout)
ERROR: Delete all breakpoints in delete_breakpoints (timeout)
FAIL: gdb.base/watchpoint.exp: watch tests suppressed
FAIL: gdb.base/watchpoint.exp: (timeout) disable fast watches
FAIL: gdb.base/watchpoint.exp: (timeout) show disable fast watches
FAIL: gdb.base/watchpoint.exp: (timeout) set slow conditional watch
FAIL: gdb.base/watchpoint.exp: (timeout) trigger slow conditional watch
FAIL: gdb.base/watchpoint.exp: (timeout) rwatch disallowed when can-use-hw-watchpoints cleared
ERROR: Delete all breakpoints in delete_breakpoints (timeout)

                === gdb Summary ===

# of expected passes            7
# of unexpected failures        7
# of unresolved testcases       5
.../sources/gdb/testsuite/../../gdb/gdb version  6.8.50.20080302-cvs -nx


...
(gdb) PASS: gdb.base/watchpoint.exp: disable watchpoint in test_simple_watchpoint
run
Starting program: /home/jkratoch/redhat/sources/gdb/testsuite/gdb.base/watchpoint
Error in re-setting breakpoint 1: Cannot access memory at address 0x86c
Error in re-setting breakpoint 2: Cannot access memory at address 0x872
Error in re-setting breakpoint 3: Cannot access memory at address 0x20127c
Error in re-setting breakpoint 1: Cannot access memory at address 0x86c
Error in re-setting breakpoint 2: Cannot access memory at address 0x872
Error in re-setting breakpoint 3: Cannot access memory at address 0x20127c
Error in re-setting breakpoint 1: Cannot access memory at address 0x86c
Error in re-setting breakpoint 2: Cannot access memory at address 0x872
Error in re-setting breakpoint 3: Cannot access memory at address 0x20127c

Program exited normally.
(gdb) FAIL: gdb.base/watchpoint.exp: run to marker1 in test_simple_watchpoint
info watch
*** glibc detected *** /home/jkratoch/redhat/sources/gdb/testsuite/../../gdb/gdb: double free or corruption (!prev): 0x00000000023f9d20 ***
======= Backtrace: =========
/lib64/libc.so.6[0x3b98672832]
/lib64/libc.so.6(cfree+0x8c)[0x3b98675f2c]
/home/jkratoch/redhat/sources/gdb/testsuite/../../gdb/gdb(xfree+0x1c)[0x44efb6]
/home/jkratoch/redhat/sources/gdb/testsuite/../../gdb/gdb(free_all_values+0x2a)[0x4cd65a]
/home/jkratoch/redhat/sources/gdb/testsuite/../../gdb/gdb(execute_command+0x26)[0x44b9df]
...

2008-03-02  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* breakpoint.c (update_watchpoint): Move B->VAL setting behind the
	VALUE_CONTENTS call.

--- ./gdb/breakpoint.c	27 Feb 2008 20:27:49 -0000	1.304
+++ ./gdb/breakpoint.c	2 Mar 2008 08:27:20 -0000
@@ -913,13 +917,15 @@ update_watchpoint (struct breakpoint *b,
 	 during evaluation, and set watchoints at addresses as needed.
 	 Those values are explicitly deleted here.  */
       v = evaluate_expression (b->exp);
+      /* Fetch the value first as if ti fails and breaks out by the exception
+         there will be no stale V left in B->VAL.  */
+      value_contents (v);
       /* Avoid setting b->val if it's already set.  The meaning of
 	 b->val is 'the last value' user saw, and we should update
 	 it only if we reported that last value to user.  As it
 	 happens, the code that reports it updates b->val directly.  */
       if (b->val == NULL)
 	b->val = v;
-      value_contents (v);
       value_release_to_mark (mark);
 
       /* Look at each value on the value chain.  */