Today I was debugging a development branch of Freecell Solver (I see Muli is
preparing the graggers) and had to deal with a problem that the scanning dump
deviated from that in the stable version. Comparing the two dumps yielded that
some derived states were not followed. But I wanted to know what generates
them?
I decided to use gdb and its scripting facilities to automate the lookup. The
end result was this script:
{{{{{{{{{{{{{{{
set args -l gi -s -i -p -t 1941.board
# Breakpoint 1
b main
r
# Breakpoint 2
b scans.c:1127 if instance->num_times == 3150
b scans.c:1139 if instance->num_times == 3150
c
# Now we are before the check.
SET $VERDICT = 0
while ($VERDICT == 0)
set $START = derived.num_states
c
set $END = derived.num_states
set $I = $START
while (($VERDICT == 0) && ($I < $END))
call fc_solve_state_as_string(derived.states[$I], 4, 8, 1, 1, 0, 1)
SET $STATE_STR = $
call strstr($STATE_STR , ": 9D 6S 4D AH\n")
SET $IS_SUBSTRING1 = $
call strstr($STATE_STR, "Freecells: 4S AC KH")
SET $IS_SUBSTRING2 = $
if ( $IS_SUBSTRING1 && $IS_SUBSTRING2 )
SET $VERDICT = 1
else
set $I = $I + 1
end
end
if ($VERDICT == 0)
c
end
end
}}}}}}}}}}}}}}}
(it operates against revision 1223 of:
http://svn.berlios.de/svnroot/repos/fc-solve/trunk/fc-solve/source/
)
This is the first time I learned about gdb's $NAME variables and assignment to
them using "set". Ideas for improvements in the next time I'm writing such
scripts would be welcome.
The end result? This patchlet:
{{{{{{{{{{{{{
Index: scans.c
===================================================================
--- scans.c (revision 1222)
+++ scans.c (revision 1223)
@@ -1250,8 +1250,8 @@
pack = (fcs_standalone_state_ptrs_t *)malloc(sizeof(*pack));
- pack->key = ptr_state_with_locations_key;
- pack->val = ptr_state_with_locations_val;
+ pack->key = derived.states[derived_index].key;
+ pack->val = derived.states[derived_index].val;
fc_solve_PQueuePush(
a_star_pqueue,
}}}}}}}}}}}}}
A small copy-and-paste error that was the difference between failure and
success.
According to http://tromey.com/blog/?p=412 , there is an upcoming Python
support in gdb, which should allow even more awesome debugger scripting. We're
so lucky to have gdb which is command-line and scriptable, because many
debuggers are neither.
Now if gdb switched away from CVS so I can contribute to it with ease. (That
or git-cvsimport won't get stuck trying to import its CVS repository.).
Regards,
Shlomi Fish
--
-----------------------------------------------------------------
Shlomi Fish http://www.shlomifish.org/
Why I Love Perl - http://xrl.us/bjn88
God gave us two eyes and ten fingers so we will type five times as much as we
read.
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