Re: [PATCH 2/6] x86: kaslr: move CPU flags out of cpucheck

[H. Peter Anvin]

On 04/26/2013 12:03 PM, Kees Cook wrote:
> +
> +static inline void cpuid(u32 id, u32 *a, u32 *b, u32 *c, u32 *d)
> +{
> +	/* Handle x86_32 PIC using ebx. */
> +	asm volatile("movl %%ebx, %%edi	\n\t"
> +		     "cpuid		\n\t"
> +		     "xchgl %%edi, %%ebx\n\t"
> +		    : "=a" (*a),
> +		      "=D" (*b),
> +		      "=c" (*c),
> +		      "=d" (*d)
> +		    : "a" (id)
> +	);
> +}

Please don't constrain registers unnecessarily.

You can use "=r" there and let gcc assign whatever free register it pleases.

You can also limit that to only:

#if defined(__i386__) && defined(__PIC__)

	-hpa

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