x86: Correct index_cpu_LZCNT [BZ # 23456]

Message ID 20180726164650.6543-1-hjl.tools@gmail.com
State New
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Series
  • x86: Correct index_cpu_LZCNT [BZ # 23456]
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Commit Message

H.J. Lu July 26, 2018, 4:46 p.m.
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(-)

-- 
2.17.1

Comments

Carlos O'Donell July 26, 2018, 6:05 p.m. | #1
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

>
H.J. Lu July 26, 2018, 6:13 p.m. | #2
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.


-- 
H.J.

Patch

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