linux-kernel - Re: [PATCH] x86/perf : Add check for CPUID instruction before using

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Date:   Fri, 2 Feb 2018 15:37:31 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Matthew Whitehead <tedheadster@...il.com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/perf : Add check for CPUID instruction before using

On Fri, Feb 02, 2018 at 09:30:51AM -0500, Matthew Whitehead wrote:
> We still officially support the ancient i486 cpu. First generation
> versions of this processor do not have the CPUID instruction, though
> later versions do. Therefore you must check that the cpu supports
> it before using it. At present it fails with an "Illegal Instruction"
> signal on the early processors.
> 
> This code was based on similar code in the gcc package.
> 
> Signed-off-by: Matthew Whitehead <tedheadster@...il.com>
> ---
>  tools/perf/arch/x86/util/header.c | 51 +++++++++++++++++++++++++++++++++++++++
>  tools/perf/util/header.h          |  2 ++
>  2 files changed, 53 insertions(+)
> 
> diff --git a/tools/perf/arch/x86/util/header.c b/tools/perf/arch/x86/util/header.c
> index fb0d71afee8b..d4d12894c64d 100644
> --- a/tools/perf/arch/x86/util/header.c
> +++ b/tools/perf/arch/x86/util/header.c
> @@ -7,6 +7,54 @@
>  
>  #include "../../util/header.h"
>  
> +/* This code based on gcc cpuid.h __get_cpuid_max() */
> +unsigned int have_cpuid(void)

You could've copied have_cpuid_p() from arch/x86/kernel/cpu/common.c

> +{
> +	unsigned int __eax, __ebx;
> +
> +#ifndef __x86_64__
> +/* See if we can use cpuid.  On AMD64 we always can.  */
> +#if __GNUC__ >= 3
> +	__asm__ ("pushf{l|d}\n\t"
> +		"pushf{l|d}\n\t"
> +		"pop{l}\t%0\n\t"
> +		"mov{l}\t{%0, %1|%1, %0}\n\t"
> +		"xor{l}\t{%2, %0|%0, %2}\n\t"
> +		"push{l}\t%0\n\t"
> +		"popf{l|d}\n\t"
> +		"pushf{l|d}\n\t"
> +		"pop{l}\t%0\n\t"
> +		"popf{l|d}\n\t"
> +		: "=&r" (__eax), "=&r" (__ebx)
> +		: "i" (0x00200000));
> +#else
> +/* Host GCCs older than 3.0 weren't supporting Intel asm syntax
> + * nor alternatives in i386 code.

We don't support gcc < 3

#if GCC_VERSION < 30200
# error Sorry, your compiler is too old - please upgrade it.
#endif

There's even talk currently to raise the minimum version to 4.9 or so.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.