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

[Juergen Gross <juergen.gross@ts.fujitsu.com>]

On 10.09.2013 14:48, Ian Campbell wrote:
> On Tue, 2013-09-10 at 13:23 +0100, Jan Beulich wrote:
>>>>> On 10.09.13 at 11:29, Andrew Cooper <andrew.cooper3@citrix.com> 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;
> }

-Wextra is needed to produce an error:
http://gcc.gnu.org/onlinedocs/gcc-4.7.3/gcc/Warning-Options.html#Warning-Options


Juergen

-- 
Juergen Gross                 Principal Developer Operating Systems
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