Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755214AbZDNHqU (ORCPT ); Tue, 14 Apr 2009 03:46:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752264AbZDNHqE (ORCPT ); Tue, 14 Apr 2009 03:46:04 -0400 Received: from mtagate4.de.ibm.com ([195.212.29.153]:52092 "EHLO mtagate4.de.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751984AbZDNHqC (ORCPT ); Tue, 14 Apr 2009 03:46:02 -0400 Date: Tue, 14 Apr 2009 09:45:56 +0200 From: Martin Schwidefsky To: Linus Torvalds Cc: Al Viro , Ingo Molnar , Tejun Heo , Mike Travis , Christoph Lameter , Heiko Carstens , Linux Kernel Mailing List , Ivan Kokshaysky Subject: Re: [PATCH] unbreak alpha percpu Message-ID: <20090414094556.3af71358@skybase> In-Reply-To: References: <20090410151224.GM26366@ZenIV.linux.org.uk> <20090410154704.GN26366@ZenIV.linux.org.uk> Organization: IBM Corporation X-Mailer: Claws Mail 3.7.1 (GTK+ 2.14.7; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2541 Lines: 65 On Fri, 10 Apr 2009 09:21:08 -0700 (PDT) Linus Torvalds wrote: > > Hmm. I certainly personally _much_ prefer this version. > > It looks like this actually simplifies things for S390 too (no more > simple_identifier_##var games), and generally just looks better. And > seeing that the S390 special case is no longer S390-specific is also a > good sign, imho. > > Sorry for including the whole message, but I'm adding s390 and percpu > people to the cc. Guys - original uncorrupted patch on lkml. > > diff --git a/arch/s390/include/asm/percpu.h b/arch/s390/include/asm/percpu.h > > index 408d60b..6a71d73 100644 > > --- a/arch/s390/include/asm/percpu.h > > +++ b/arch/s390/include/asm/percpu.h > > @@ -13,20 +13,18 @@ > > */ > > #if defined(__s390x__) && defined(MODULE) > > > > -#define SHIFT_PERCPU_PTR(ptr,offset) (({ \ > > - extern int simple_identifier_##var(void); \ > > +#define SHIFT_PERCPU_PTR(var,offset) (({ \ > > unsigned long *__ptr; \ > > asm ( "larl %0, %1@GOTENT" \ > > - : "=a" (__ptr) : "X" (ptr) ); \ > > - (typeof(ptr))((*__ptr) + (offset)); })) > > + : "=a" (__ptr) : "X" (&per_cpu_var(var)) ); \ > > + (typeof(&per_cpu_var(var)))((*__ptr) + (offset)); })) > > > > #else > > > > -#define SHIFT_PERCPU_PTR(ptr, offset) (({ \ > > - extern int simple_identifier_##var(void); \ > > +#define SHIFT_PERCPU_PTR(var, offset) (({ \ > > unsigned long __ptr; \ > > - asm ( "" : "=a" (__ptr) : "0" (ptr) ); \ > > - (typeof(ptr)) (__ptr + (offset)); })) > > + asm ( "" : "=a" (__ptr) : "0" (&per_cpu_var(var)) ); \ > > + (typeof(&per_cpu_var(var))) (__ptr + (offset)); })) > > > > #endif > > I would like to get rid of that SHIFT_PERCPU_PTR mess. The patch from Ivan will allow this, it uses a dummy variable to void the effect of a static modifier for percpu variables in modules. The percpu variable itself will be defined non-static, my gut feeling is that this is a dirty little trick that might bite us in the future. Another solution which I personally would prefer is to ban the use of static percpu variables. Then the compiler will use the GOT to get the address of percpu variables without any dirty tricks. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/