linux-kernel - Re: [PATCH] x86, kvm: Remove incorrect redundant assembly constraint

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Date:	Mon, 26 Nov 2012 08:22:45 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>
CC:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	Gleb Natapov <gleb@...hat.com>,
	Linux KVM mailing list <kvm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86, kvm: Remove incorrect redundant assembly constraint

Il 21/11/2012 23:41, H. Peter Anvin ha scritto:
> From: "H. Peter Anvin" <hpa@...ux.intel.com>
> 
> In __emulate_1op_rax_rdx, we use "+a" and "+d" which are input/output
> constraints, and *then* use "a" and "d" as input constraints.  This is
> incorrect, but happens to work on some versions of gcc.
> 
> However, it breaks gcc with -O0 and icc, and may break on future
> versions of gcc.
> 
> Reported-and-tested-by: Melanie Blower <melanie.blower@...el.com>
> Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
> Link: http://lkml.kernel.org/r/B3584E72CFEBED439A3ECA9BCE67A4EF1B17AF90@FMSMSX107.amr.corp.intel.com
> ---
>  arch/x86/kvm/emulate.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 39171cb..bba39bf 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -426,8 +426,7 @@ static void invalidate_registers(struct x86_emulate_ctxt *ctxt)
>  			_ASM_EXTABLE(1b, 3b)				\
>  			: "=m" ((ctxt)->eflags), "=&r" (_tmp),		\
>  			  "+a" (*rax), "+d" (*rdx), "+qm"(_ex)		\
> -			: "i" (EFLAGS_MASK), "m" ((ctxt)->src.val),	\
> -			  "a" (*rax), "d" (*rdx));			\
> +			: "i" (EFLAGS_MASK), "m" ((ctxt)->src.val));	\
>  	} while (0)
>  
>  /* instruction has only one source operand, destination is implicit (e.g. mul, div, imul, idiv) */
> 

Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
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