From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757869AbYFTUFq (ORCPT ); Fri, 20 Jun 2008 16:05:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756943AbYFTUFf (ORCPT ); Fri, 20 Jun 2008 16:05:35 -0400 Received: from gw.goop.org ([64.81.55.164]:54838 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755454AbYFTUFe (ORCPT ); Fri, 20 Jun 2008 16:05:34 -0400 Message-ID: <485C0D8A.6030500@goop.org> Date: Fri, 20 Jun 2008 13:05:30 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: Ingo Molnar CC: Linus Torvalds , benh@kernel.crashing.org, xen-devel , Peter Zijlstra , kvm-devel , x86@kernel.org, LKML , Virtualization Mailing List , Hugh Dickins , Thomas Gleixner Subject: Re: [PATCH 1 of 4] mm: add a ptep_modify_prot transaction abstraction References: <4859AA47.2020903@goop.org> <20080619115832.GM15228@elte.hu> <20080619164708.GA32190@elte.hu> <20080620101028.GA23664@elte.hu> <485BFFC4.3070902@goop.org> <20080620195620.GA20183@elte.hu> In-Reply-To: <20080620195620.GA20183@elte.hu> X-Enigmail-Version: 0.95.6 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Ingo Molnar wrote: > * Linus Torvalds wrote: > > >> On Fri, 20 Jun 2008, Jeremy Fitzhardinge wrote: >> >>> Blows up on "gcc version 3.4.4 20050314 (prerelease) (Debian 3.4.3-13)": >>> >> Yeah, I was a bit worried about that. Gcc sometimes does insane >> things. >> >> We literally just tested that the asm should only _ever_ be generated >> with a constant value, but if some gcc dead-code removal thing doesn't >> work, it will then screw up and try to generate the asm even for a >> non-constant thing. >> >> The fairly trivial fix is probably to just change the "i" to "ir", >> safe in the knowledge that any _sane_ case will never use the "r" >> possibility. I suspect even your insane case will end up then killing >> the bad choice later. >> > > okay - Jeremy, could you try the fix below? (or tip/master, i just > pushed this out) > > Hm. On 32-bit I get these, but they're warnings. On 64-bit they're errors. {standard input}: Assembler messages: {standard input}:1609: Warning: using `%dl' instead of `%edx' due to `b' suffix vs {standard input}: Assembler messages: {standard input}:20511: Error: Incorrect register `%eax' used with `b' suffix > (i dont use gcc 3.x myself to build the kernel, had way too many > miscompilations in randconfig tests in the past.) > I do it mainly to pick up these kinds of problems. > Ingo > > --------------> > commit b68b80b8ab39c42707dc126c41e87d46edc97c27 > Author: Ingo Molnar > Date: Fri Jun 20 21:50:20 2008 +0200 > > x86, bitops: make constant-bit set/clear_bit ops faster, gcc workaround > > Jeremy Fitzhardinge reported this compiler bug: > > Suggestion from Linus: add "r" to the input constraint of the > set_bit()/clear_bit()'s constant 'nr' branch: > > Blows up on "gcc version 3.4.4 20050314 (prerelease) (Debian 3.4.3-13)": > > CC init/main.o > include2/asm/bitops.h: In function `start_kernel': > include2/asm/bitops.h:59: warning: asm operand 1 probably doesn't match constraints > include2/asm/bitops.h:59: warning: asm operand 1 probably doesn't match constraints > include2/asm/bitops.h:59: warning: asm operand 1 probably doesn't match constraints > include2/asm/bitops.h:59: error: impossible constraint in `asm' > include2/asm/bitops.h:59: error: impossible constraint in `asm' > include2/asm/bitops.h:59: error: impossible constraint in `asm' > > Reported-by: Jeremy Fitzhardinge > Signed-off-by: Ingo Molnar > > diff --git a/include/asm-x86/bitops.h b/include/asm-x86/bitops.h > index 6c50548..4575de4 100644 > --- a/include/asm-x86/bitops.h > +++ b/include/asm-x86/bitops.h > @@ -58,7 +58,7 @@ static inline void set_bit(unsigned int nr, volatile unsigned long *addr) > if (IS_IMMEDIATE(nr)) { > asm volatile(LOCK_PREFIX "orb %1,%0" > : CONST_MASK_ADDR(nr, addr) > - : "i" (CONST_MASK(nr)) > + : "ir" (CONST_MASK(nr)) > : "memory"); > } else { > asm volatile(LOCK_PREFIX "bts %1,%0" > @@ -95,7 +95,7 @@ static inline void clear_bit(int nr, volatile unsigned long *addr) > if (IS_IMMEDIATE(nr)) { > asm volatile(LOCK_PREFIX "andb %1,%0" > : CONST_MASK_ADDR(nr, addr) > - : "i" (~CONST_MASK(nr))); > + : "ir" (~CONST_MASK(nr))); > } else { > asm volatile(LOCK_PREFIX "btr %1,%0" > : BITOP_ADDR(addr) >