< August 2008 >
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Tue, 05 Aug 2008:

Frustration is my fuel. I spent an all nighter re-doing up one of my old valgrind patches to work with valgrind-3.3.1. This one was a doozy to patch up the first time (stealing rwalsh's code), but not quite very hard to keep up with the releases. The patch needs to be applied to the 3.3.1 source tree and memcheck rebuilt. It also requires the target code to be instrumented.

#include "valgrind/memcheck.h"

static int foobar = 1;

int main()
	int *x = malloc(sizeof(int));
	int wpid = VALGRIND_SET_WATCHPOINT(x, sizeof(int), &foobar);
	*x = 10;
	foobar = 0;
	*x = 10;

What has been added anew is the foobar conditional (you could just pass in NULL, if you always want an error). In this case the error is thrown only in first line modifying x. Setting the conditional to zero turns off the error reporting.

With the new APC-3.1 branch, I'm again hitting new race conditions whenever I change around stuff. I have no real way of debugging it in a controlled environment. But this patch will let me protect the entire shared memory space and turn on error flag as soon as control exits APC. Just being able to log all unlocked writes from Zend should go a long way in being able to track down race conditions.

Yup, frustration is my fuel.

An intellectual is someone whose mind watches itself.
                -- Albert Camus

posted at: 05:44 | path: /hacks | permalink | Tags: , ,