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

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

[Forrest Voight]

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 */

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

[Michael Tokarev]

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

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

[Oleg Verych]

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'.