Re: [Xen-devel] [PATCH] libxc/pm: Fix NULL pointer checks.

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2013-09-10 at 13:23 +0100, Jan Beulich wrote:
> >>> On 10.09.13 at 11:29, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> > --- a/tools/libxc/xc_pm.c
> > +++ b/tools/libxc/xc_pm.c
> > @@ -285,7 +285,7 @@ int xc_set_cpufreq_gov(xc_interface *xch, int cpuid, 
> > char *govname)
> >      DECLARE_SYSCTL;
> >      char *scaling_governor = sysctl.u.pm_op.u.set_gov.scaling_governor;
> >  
> > -    if ( (xch < 0) || (!govname) )
> > +    if ( !xch || !govname )
> 
> I'm very surprised the compiler didn't reject this - I'm unaware of
> an extension that would allow pointers to be compared by other
> than == and != (plus it's all but clear what e.g. a "negative"
> pointer really is).

We were just discussing this at lunch and couldn't work it out either,
but indeed both gcc 4.7.[23] and clang 3.2 accept this when building
with -Wall:
int main(int argc, char **argv)
{
        if ( argv[1] < 0 )
                printf("ARGV[1] < 0\n");
        else
                printf("ARGV[1] >= 0\n");
        return 0;
}

Ian.


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