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Date:   Fri, 2 Feb 2018 11:54:48 -0300
From:   Arnaldo Carvalho de Melo <acme@kernel.org>
To:     Matthew Whitehead <tedheadster@gmail.com>
Cc:     peterz@infradead.org, mingo@redhat.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/perf : Add check for CPUID instruction before using
Message-ID: <20180202145448.GD26905@kernel.org>
References: <1517581851-6600-1-git-send-email-tedheadster@gmail.com>
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Em Fri, Feb 02, 2018 at 09:30:51AM -0500, Matthew Whitehead escreveu:
> 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.

Can you provide an URL for the code used as a reference, please?

- Arnaldo
 
> Signed-off-by: Matthew Whitehead <tedheadster@gmail.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)
> +{
> +	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.
> + */
> +	__asm__ ("pushfl\n\t"
> +		"pushfl\n\t"
> +		"popl\t%0\n\t"
> +		"movl\t%0, %1\n\t"
> +		"xorl\t%2, %0\n\t"
> +		"pushl\t%0\n\t"
> +		"popfl\n\t"
> +		"pushfl\n\t"
> +		"popl\t%0\n\t"
> +		"popfl\n\t"
> +		: "=&r" (__eax), "=&r" (__ebx)
> +		: "i" (0x00200000));
> +#endif
> +
> +	if (!((__eax ^ __ebx) & 0x00200000))
> +		return 0;
> +	else
> +		return 1;
> +#endif
> +
> +/* All x86_64 support cpuid */
> +	return 1;
> +}
> +
>  static inline void
>  cpuid(unsigned int op, unsigned int *a, unsigned int *b, unsigned int *c,
>        unsigned int *d)
> @@ -28,6 +76,9 @@ __get_cpuid(char *buffer, size_t sz, const char *fmt)
>  	int nb;
>  	char vendor[16];
>  
> +	if (!have_cpuid())
> +		return -1;
> +
>  	cpuid(0, &lvl, &b, &c, &d);
>  	strncpy(&vendor[0], (char *)(&b), 4);
>  	strncpy(&vendor[4], (char *)(&d), 4);
> diff --git a/tools/perf/util/header.h b/tools/perf/util/header.h
> index f28aaaa3a440..ce31fca36077 100644
> --- a/tools/perf/util/header.h
> +++ b/tools/perf/util/header.h
> @@ -171,6 +171,8 @@ int write_padded(struct feat_fd *fd, const void *bf,
>  /*
>   * arch specific callback
>   */
> +unsigned int have_cpuid(void);
> +
>  int get_cpuid(char *buffer, size_t sz);
>  
>  char *get_cpuid_str(struct perf_pmu *pmu __maybe_unused);
> -- 
> 2.13.6