x86: Correct index_cpu_LZCNT [BZ # 23456]

  cpu-features.h has

 #define bit_cpu_LZCNT		(1 << 5)
 #define index_cpu_LZCNT	COMMON_CPUID_INDEX_1
 #define reg_LZCNT

But the LZCNT feature bit is in COMMON_CPUID_INDEX_80000001:

Initial EAX Value: 80000001H
ECX Extended Processor Signature and Feature Bits:
Bit 05: LZCNT available

index_cpu_LZCNT should be COMMON_CPUID_INDEX_80000001, not
COMMON_CPUID_INDEX_1.  The VMX feature bit is in COMMON_CPUID_INDEX_1:

Initial EAX Value: 01H
Feature Information Returned in the ECX Register:
5 VMX

	[BZ # 23456]
	* sysdeps/x86/cpu-features.h (index_cpu_LZCNT): Set to
	COMMON_CPUID_INDEX_80000001.
---
 sysdeps/x86/cpu-features.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
  

On 07/26/2018 12:46 PM, H.J. Lu wrote:
> cpu-features.h has
> 
>  #define bit_cpu_LZCNT		(1 << 5)
>  #define index_cpu_LZCNT	COMMON_CPUID_INDEX_1
>  #define reg_LZCNT
> 
> But the LZCNT feature bit is in COMMON_CPUID_INDEX_80000001:
> 
> Initial EAX Value: 80000001H
> ECX Extended Processor Signature and Feature Bits:
> Bit 05: LZCNT available
> 
> index_cpu_LZCNT should be COMMON_CPUID_INDEX_80000001, not
> COMMON_CPUID_INDEX_1.  The VMX feature bit is in COMMON_CPUID_INDEX_1:
> 
> Initial EAX Value: 01H
> Feature Information Returned in the ECX Register:
> 5 VMX
> 
> 	[BZ # 23456]
> 	* sysdeps/x86/cpu-features.h (index_cpu_LZCNT): Set to
> 	COMMON_CPUID_INDEX_80000001.

OK for 2.28.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

> ---
>  sysdeps/x86/cpu-features.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/sysdeps/x86/cpu-features.h b/sysdeps/x86/cpu-features.h
> index 624e681e96..3807a9d611 100644
> --- a/sysdeps/x86/cpu-features.h
> +++ b/sysdeps/x86/cpu-features.h
> @@ -204,7 +204,7 @@ extern const struct cpu_features *__get_cpu_features (void)
>  # define index_cpu_HTT		COMMON_CPUID_INDEX_1
>  # define index_cpu_BMI1		COMMON_CPUID_INDEX_7
>  # define index_cpu_BMI2		COMMON_CPUID_INDEX_7
> -# define index_cpu_LZCNT	COMMON_CPUID_INDEX_1
> +# define index_cpu_LZCNT	COMMON_CPUID_INDEX_80000001

Confirmed.

CPUID.EAX=80000001H:ECX.LZCNT[bit 5]: if 1 indicates the processor supports the LZCNT instruction.

>  # define index_cpu_MOVBE	COMMON_CPUID_INDEX_1
>  # define index_cpu_POPCNT	COMMON_CPUID_INDEX_1
>  # define index_cpu_IBT		COMMON_CPUID_INDEX_7
>
  

On Thu, Jul 26, 2018 at 11:05 AM, Carlos O'Donell <carlos@redhat.com> wrote:
> On 07/26/2018 12:46 PM, H.J. Lu wrote:
>> cpu-features.h has
>>
>>  #define bit_cpu_LZCNT                (1 << 5)
>>  #define index_cpu_LZCNT      COMMON_CPUID_INDEX_1
>>  #define reg_LZCNT
>>
>> But the LZCNT feature bit is in COMMON_CPUID_INDEX_80000001:
>>
>> Initial EAX Value: 80000001H
>> ECX Extended Processor Signature and Feature Bits:
>> Bit 05: LZCNT available
>>
>> index_cpu_LZCNT should be COMMON_CPUID_INDEX_80000001, not
>> COMMON_CPUID_INDEX_1.  The VMX feature bit is in COMMON_CPUID_INDEX_1:
>>
>> Initial EAX Value: 01H
>> Feature Information Returned in the ECX Register:
>> 5 VMX
>>
>>       [BZ # 23456]
>>       * sysdeps/x86/cpu-features.h (index_cpu_LZCNT): Set to
>>       COMMON_CPUID_INDEX_80000001.
>
> OK for 2.28.
>
> Reviewed-by: Carlos O'Donell <carlos@redhat.com>

Done.  We also need this for 2.28:

https://sourceware.org/ml/libc-alpha/2018-07/msg00914.html

Otherwise, we fail to detect LZCNT on Intel CPUs.