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Re: [Xen-devel] [PATCH] libxc/pm: Fix NULL pointer checks.
- To: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
- From: Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>
- Date: Tue, 10 Sep 2013 15:03:49 +0200
- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 10 Sep 2013 13:09:06 +0000
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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@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;
}
-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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Fujitsu Technology Solutions e-mail: juergen.gross@xxxxxxxxxxxxxx
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