From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: [PATCH] x86/time: fix scale_delta() inline assembly Date: Mon, 26 Nov 2012 16:10:53 +0000 Message-ID: References: <50B3978F02000078000AB3A3@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <50B3978F02000078000AB3A3@nat28.tlf.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich , xen-devel List-Id: xen-devel@lists.xenproject.org On 26/11/2012 15:23, "Jan Beulich" wrote: > The way it was coded, it clobbered %rdx without telling the compiler. > This generally didn't cause any problems except when there are two back > to back invocations (as in plt_overflow()), as in that case the > compiler may validly assume that it can re-use for the second instance > the value loaded into %rdx before the first one. > > Once at it, also properly relax the second operand of "mul" (there's no > need for it to be in %rdx, or a register at all), and switch away from > using explicit register names in the instruction operands. > > Signed-off-by: Jan Beulich Ugh. Thank you very much, Jan! What a horrible bug. Acked-by: Keir Fraser > --- a/xen/arch/x86/time.c > +++ b/xen/arch/x86/time.c > @@ -127,8 +127,9 @@ static inline u64 scale_delta(u64 delta, > delta <<= scale->shift; > > asm ( > - "mul %%rdx ; shrd $32,%%rdx,%%rax" > - : "=a" (product) : "0" (delta), "d" ((u64)scale->mul_frac) ); > + "mul %2 ; shrd $32,%1,%0" > + : "=a" (product), "=d" (delta) > + : "rm" (delta), "0" ((u64)scale->mul_frac) ); > > return product; > } > > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xen.org > http://lists.xen.org/xen-devel