Erick Mattos wrote:
> 2010/6/10 Thomas Rast <trast@xxxxxxxxxxxxxxx>
> > -int log_ref_setup(const char *ref_name, char **log_file)
> > +int log_ref_setup(const char *ref_name, char *logfile, int bufsize)
> > {
> > int logfd, oflags = O_APPEND | O_WRONLY;
> > - char logfile[PATH_MAX];
> >
> > - git_snpath(logfile, sizeof(logfile), "logs/%s", ref_name);
> > - *log_file = logfile;
> > + git_snpath(logfile, bufsize, "logs/%s", ref_name);
[...]
> I don't see any improvement here. Unless you want to get rid of using
> references on calling functions which is only going to add another
> buffer to the stack, sized PATH_MAX, once that log_file is going to be
> really allocated in the heap after git_snpath(). As folks use to say
> here: "changing six by half a dozen".
What the - side of the hunk above does is returning a local (stack
allocated) variable, in the form of a pointer to logfile. Once those
go out of scope, you have zero guarantees on what happens with them.
Try the following snippet, it should cause a similar problem:
#include <stdio.h>
int* f()
{
int i;
i = 42;
return &i;
}
int main()
{
int *p = f();
if (1) {
char buf[1024];
memset(buf, 0, sizeof(buf));
}
printf("I got: %d\n", *p);
}
Only in this case the issue is so obvious that the compiler will warn
(at least mine does).
> I haven't ever seen this happening so I think you have found some
> particularity of valgrind which could route a patch to it.
Admittedly my experience is somewhat limited since I don't do C coding
outside of git and some teaching. But so far I have not had a single
false alarm with valgrind (when compiled without optimizations;
otherwise the compiler may do some magic).
--
Thomas Rast
trast@{inf,student}.ethz.ch
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