On Saturday 28 November 2009 01:06:30 Kevin Day wrote:
> On Fri, Nov 27, 2009 at 2:45 PM, Rob Landley <[email protected]> wrote:
> > On Friday 27 November 2009 11:45:50 Kevin Day wrote:
> >> I was looking at uClibc 0.9.28.3 to try and apply this patch and
> >> noticed:
> >>
> >> At the very end of your patch, the untouched code only has
> >> free(packet); while 0.9.28.3 has:
> >> if (packet)
> >> free(packet);
> >>
> >> Does anybody know why was this safety check removed?
> >
> > From the Single Unix Specification version 4 (I.E. SUSv4, I.E. POSIX
> > 2008):
> >
> > http://www.opengroup.org/onlinepubs/9699919799/functions/free.html
> >
> > > If ptr is a null pointer, no action shall occur.
> >
> > I.E. free() has a null check built-in, as required by POSIX.
> >
> > Rob
> > --
> > Latency is more important than throughput. It's that simple. - Linus
> > Torvalds
>
> So you are saying a double-free cannot happen here?
I'm saying that freeing a NULL pointer is a NOP, so testing for NULL before
calling free() is a waste of bytes.
What does a double-free have to do with this? If the pointer is NULL, then
there's nothing to free. If the pointer isn't NULL, the test isn't relevant.
Legal (and pointless) code:
void does_nothing(void)
{
x=NULL;
free(x);
free(x);
free(x);
}
Rob
--
Latency is more important than throughput. It's that simple. - Linus Torvalds
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