2006-08-09 17:49:04

by Forrest Voight

Subject: [PATCH] arch/i386/kernel/cpu/transmeta.c, kernel 2.6.17.8

Corrects warning:

CC arch/i386/kernel/cpu/centaur.o
CC arch/i386/kernel/cpu/transmeta.o
arch/i386/kernel/cpu/transmeta.c: In function 'init_transmeta':
arch/i386/kernel/cpu/transmeta.c:12: warning: 'cpu_freq' may be used
uninitialized in this function
CC arch/i386/kernel/cpu/intel.o



--- linux-2.6.17.8/arch/i386/kernel/cpu/transmeta.c 2006-08-07
00:18:54.000000000 -0400
+++ linux/arch/i386/kernel/cpu/transmeta.c 2006-08-09
13:32:05.000000000 -0400
@@ -9,7 +9,7 @@
{
unsigned int cap_mask, uk, max, dummy;
unsigned int cms_rev1, cms_rev2;
- unsigned int cpu_rev, cpu_freq, cpu_flags, new_cpu_rev;
+ unsigned int cpu_rev, cpu_freq = 0, cpu_flags, new_cpu_rev;
char cpu_info[65];

get_model_name(c); /* Same as AMD/Cyrix */

2006-08-09 20:18:40

by Michael Tokarev

Subject: Re: [PATCH] arch/i386/kernel/cpu/transmeta.c, kernel 2.6.17.8

Forrest Voight wrote:
> Corrects warning:
>
> CC arch/i386/kernel/cpu/centaur.o
> CC arch/i386/kernel/cpu/transmeta.o
> arch/i386/kernel/cpu/transmeta.c: In function 'init_transmeta':
> arch/i386/kernel/cpu/transmeta.c:12: warning: 'cpu_freq' may be used
> uninitialized in this function
> CC arch/i386/kernel/cpu/intel.o
>

This is a false alarm.
Here's the code (details omitted):

if ( max >= 0x80860001 ) {
cpuid(0x80860001, &dummy, &cpu_rev, &cpu_freq, &cpu_flags);
^^^^^^^^^
}
if ( max >= 0x80860002 ) {
printk(KERN_INFO "CPU: Processor %u MHz\n", cpu_freq);
}

Note the two conditions: if second is true, the first is
true too, so both branches are executed, so first cpu_freq
is initialized (by cpuid() call) and next it's used in printk.

The same thing will be done by the following code:

if ( max >= 0x80860001 ) {
cpuid(0x80860001, &dummy, &cpu_rev, &cpu_freq, &cpu_flags);
if ( max >= 0x80860002 ) {
printk(KERN_INFO "CPU: Processor %u MHz\n", cpu_freq);
}
}

and in this case gcc will not (hopefully) issue the warning.

BTW, cpu_rev gets initialized to 0 here as well - looks like
it's done also just to prevent warning message.

/mjt

2006-08-09 23:45:09

by Oleg Verych

Subject: Re: [PATCH] arch/i386/kernel/cpu/transmeta.c, kernel 2.6.17.8

Forrest Voight:
> Corrects warning:
> arch/i386/kernel/cpu/transmeta.c: In function 'init_transmeta':
> arch/i386/kernel/cpu/transmeta.c:12: warning: 'cpu_freq' may be used
> uninitialized in this function
> - unsigned int cpu_rev, cpu_freq, cpu_flags, new_cpu_rev;
> + unsigned int cpu_rev, cpu_freq = 0, cpu_flags, new_cpu_rev;

If one doesn't want to add more init code, but variable indeed used
uninitialazed, in GCC 3.X struct may be used, GCC 4.X needs 'volatile'.