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

From: Borislav Petkov
Date: Fri Feb 02 2018 - 09:38:12 EST


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@xxxxxxxxx>
> ---
> 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.

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