diff mbox series

x86: Check if CPUID_INDEX_7_ECX_1 is supported first

Message ID CAMe9rOro-xjRjsaOsRcYrcyb5F-Lcs+gdBq-pYzwPE3UtiTsGw@mail.gmail.com (mailing list archive)
State Changes Requested
Headers
Series x86: Check if CPUID_INDEX_7_ECX_1 is supported first |

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Commit Message

H.J. Lu Aug. 25, 2026, 2:40 a.m. UTC 
  Since bits 31 - 00 in EAX from CPUID with EAX == 7 and ECX == 0 reports
the maximum input value for supported leaf 7 sub-leaves for CPUID with
EAX == 7, check it before invoking CPUID with EAX == 7 and ECX == 1.
This fixes BZ #34565.

Comments

Florian Weimer Aug. 25, 2026, 6:36 a.m. UTC | #1 
* H. J. Lu:

> diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
> index a453136827..0db33e0f35 100644
> --- a/sysdeps/x86/cpu-features.c
> +++ b/sysdeps/x86/cpu-features.c
> @@ -458,11 +458,13 @@ get_common_indices (struct cpu_features *cpu_features,
>  		     cpu_features->features[CPUID_INDEX_7].cpuid.ebx,
>  		     cpu_features->features[CPUID_INDEX_7].cpuid.ecx,
>  		     cpu_features->features[CPUID_INDEX_7].cpuid.edx);
> -      __cpuid_count (7, 1,
> -		     cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.eax,
> -		     cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.ebx,
> -		     cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.ecx,
> -		     cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.edx);
> +      if (cpu_features->features[CPUID_INDEX_7].cpuid.eax != 0)
> +	__cpuid_count
> +	  (7, 1,
> +	   cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.eax,
> +	   cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.ebx,
> +	   cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.ecx,
> +	   cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.edx);
>      }
>  
>    if (cpu_features->basic.max_cpuid >= 0xd)

If subleaf 1 is not support, should we zero the fields?

Thanks,
Florian
H.J. Lu Aug. 25, 2026, 7:03 a.m. UTC | #2 
On Tue, Aug 25, 2026 at 2:36 PM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu:
>
> > diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
> > index a453136827..0db33e0f35 100644
> > --- a/sysdeps/x86/cpu-features.c
> > +++ b/sysdeps/x86/cpu-features.c
> > @@ -458,11 +458,13 @@ get_common_indices (struct cpu_features *cpu_features,
> >                    cpu_features->features[CPUID_INDEX_7].cpuid.ebx,
> >                    cpu_features->features[CPUID_INDEX_7].cpuid.ecx,
> >                    cpu_features->features[CPUID_INDEX_7].cpuid.edx);
> > -      __cpuid_count (7, 1,
> > -                  cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.eax,
> > -                  cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.ebx,
> > -                  cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.ecx,
> > -                  cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.edx);
> > +      if (cpu_features->features[CPUID_INDEX_7].cpuid.eax != 0)
> > +     __cpuid_count
> > +       (7, 1,
> > +        cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.eax,
> > +        cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.ebx,
> > +        cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.ecx,
> > +        cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.edx);
> >      }
> >
> >    if (cpu_features->basic.max_cpuid >= 0xd)
>
> If subleaf 1 is not support, should we zero the fields?
>

_rtld_global_ro._dl_x86_cpu_features is initialized to 0.
diff mbox series

Patch

From 7f5f1bdc7fd97d165d1c41d7a83c426f4423cd1b Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Tue, 25 Aug 2026 09:43:26 +0800
Subject: [PATCH] x86: Check if CPUID_INDEX_7_ECX_1 is supported first

Since bits 31 - 00 in EAX from CPUID with EAX == 7 and ECX == 0 reports
the maximum input value for supported leaf 7 sub-leaves for CPUID with
EAX == 7, check it before invoking CPUID with EAX == 7 and ECX == 1.
This fixes BZ #34565.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
---
 sysdeps/x86/cpu-features.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index a453136827..0db33e0f35 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -458,11 +458,13 @@  get_common_indices (struct cpu_features *cpu_features,
 		     cpu_features->features[CPUID_INDEX_7].cpuid.ebx,
 		     cpu_features->features[CPUID_INDEX_7].cpuid.ecx,
 		     cpu_features->features[CPUID_INDEX_7].cpuid.edx);
-      __cpuid_count (7, 1,
-		     cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.eax,
-		     cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.ebx,
-		     cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.ecx,
-		     cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.edx);
+      if (cpu_features->features[CPUID_INDEX_7].cpuid.eax != 0)
+	__cpuid_count
+	  (7, 1,
+	   cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.eax,
+	   cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.ebx,
+	   cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.ecx,
+	   cpu_features->features[CPUID_INDEX_7_ECX_1].cpuid.edx);
     }
 
   if (cpu_features->basic.max_cpuid >= 0xd)
-- 
2.55.0