From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: [Patch 1/3 v2] x86/irq: local_irq_restore() should not blindly popf Date: Mon, 21 Oct 2013 19:37:49 +0100 Message-ID: References: <526572B6.3030803@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <526572B6.3030803@citrix.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: Andrew Cooper Cc: Jan Beulich , Xen-devel List-Id: xen-devel@lists.xenproject.org On 21/10/2013 19:30, "Andrew Cooper" wrote: >>> #define read_segment_register(name) \ >>> ({ u16 __sel; \ >>> @@ -159,15 +160,19 @@ static always_inline unsigned long __cmpxchg( >>> #define local_irq_restore(x) \ >>> ({ \ >>> BUILD_BUG_ON(sizeof(x) != sizeof(long)); \ >>> - asm volatile ( "push" __OS " %0 ; popf" __OS \ >>> - : : "g" (x) : "memory", "cc" ); \ >>> + asm volatile ( \ >>> + "pushf" __OS "\n\t" \ >>> + "and" __OS " %0, (%%" __OP "sp)\n\t" \ >>> + "orw %1, (%%" __OP "sp)\n\t" \ >>> + "popf" __OS "\n\t" : : "g" ( ~X86_EFLAGS_IF ), \ >> Would this be better as a constant constraint ("i")? > > I was wondering what the best practice for this would be. > > In most cases, I would imagine that an immediate would be used. > However, as this is a define and therefore forcibly inlined everywhere > it is used, it is just possible that the compiler could find a > ~X86_EFLAGS_IF already in context, and optimise down to an "and r64,r/m64". Oh, g includes i, I forgot that. Well your choice is best then. Acked-by: Keir Fraser > ~Andrew