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Date: Fri, 26 Apr 2013 14:47:02 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Kees Cook <keescook@...omium.org>
CC: linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
x86@...nel.org, Jarkko Sakkinen <jarkko.sakkinen@...el.com>,
Matthew Garrett <mjg@...hat.com>,
Matt Fleming <matt.fleming@...el.com>,
Eric Northup <digitaleric@...gle.com>,
Dan Rosenberg <drosenberg@...curity.com>,
Julien Tinnes <jln@...gle.com>, Will Drewry <wad@...omium.org>
Subject: Re: [PATCH 2/6] x86: kaslr: move CPU flags out of cpucheck
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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