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Date: Wed, 03 Aug 2005 20:06:32 -0700
From: Zachary Amsden <zach@vmware.com>
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To: "H. Peter Anvin" <hpa@zytor.com>
Cc: akpm@osdl.org, chrisl@vmware.com, davej@codemonkey.org.uk,
       linux-kernel@vger.kernel.org, pratap@vmware.com, Riley@Williams.Name
Subject: Re: [PATCH] 1/5 more-asm-cleanup
References: <200508040043.j740h4wB004166@zach-dev.vmware.com> <42F165BC.9030504@zytor.com>
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Please explain why this is a reject after looking at the cpuid macro.  
It changed recently.  Note 0 -> %ecx.

Would you prefer that I call cpuid_count and pass an explicit zero 
parameter for ecx?


/*
 * Generic CPUID function
 * clear %ecx since some cpus (Cyrix MII) do not set or clear %ecx
 * resulting in stale register contents being returned.
 */
static inline void cpuid(unsigned int op, unsigned int *eax, unsigned 
int *ebx, unsigned int *ecx, unsigned int *edx)
{
        __asm__("cpuid"
                : "=a" (*eax),
                  "=b" (*ebx),
                  "=c" (*ecx),
                  "=d" (*edx)
                : "0" (op), "c"(0));
}


H. Peter Anvin wrote:

> zach@vmware.com wrote:
>
>> Some more assembler cleanups I noticed along the way.
>
>
>> Index: linux-2.6.13/arch/i386/kernel/cpu/intel.c
>> ===================================================================
>> --- linux-2.6.13.orig/arch/i386/kernel/cpu/intel.c    2005-08-03 
>> 15:18:18.000000000 -0700
>> +++ linux-2.6.13/arch/i386/kernel/cpu/intel.c    2005-08-03 
>> 15:19:39.000000000 -0700
>> @@ -82,16 +82,12 @@
>>   */
>>  static int __devinit num_cpu_cores(struct cpuinfo_x86 *c)
>>  {
>> -    unsigned int eax;
>> +    unsigned int eax, ebx, ecx, edx;
>>  
>>      if (c->cpuid_level < 4)
>>          return 1;
>>  
>> -    __asm__("cpuid"
>> -        : "=a" (eax)
>> -        : "0" (4), "c" (0)
>> -        : "bx", "dx");
>> -
>> +    cpuid(4, &eax, &ebx, &ecx, &edx);
>>      if (eax & 0x1f)
>>          return ((eax >> 26) + 1);
>
>
> Reject!  This is a bogus patch; Intel's CPUID level 4 has a 
> nonstandard dependency on ECX (idiots...) and therefore this needs 
> special handling.
>
>     -hpa
>