From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932576AbcFOJdi (ORCPT ); Wed, 15 Jun 2016 05:33:38 -0400 Received: from lb2-smtp-cloud3.xs4all.net ([194.109.24.26]:34706 "EHLO lb2-smtp-cloud3.xs4all.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932485AbcFOJdg (ORCPT ); Wed, 15 Jun 2016 05:33:36 -0400 Message-ID: <1465983212.9515.35.camel@tiscali.nl> Subject: Re: linux-next: build failure after merge of the akpm-current tree From: Paul Bolle To: Andrew Morton , Arnd Bergmann Cc: Stephen Rothwell , linux-next@vger.kernel.org, linux-kernel@vger.kernel.org Date: Wed, 15 Jun 2016 11:33:32 +0200 In-Reply-To: <20160505224429.3b8f3837bcb0281932cfe03f@linux-foundation.org> References: <20160506145810.04a319d3@canb.auug.org.au> <20160505224429.3b8f3837bcb0281932cfe03f@linux-foundation.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.16.5 (3.16.5-3.fc22) Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On do, 2016-05-05 at 22:44 -0700, Andrew Morton wrote: > From: Arnd Bergmann > Subject: byteswap: try to avoid __builtin_constant_p gcc bug > > This is another attempt to avoid a regression in wwn_to_u64() after that > started using get_unaligned_be64(), which in turn ran into a bug on > gcc-4.9 through 6.1. > > The regression got introduced due to the combination of two separate > workarounds (e3bde9568d99 ("include/linux/unaligned: force inlining of > byteswap operations") and ef3fb2422ffe ("scsi: fc: use get/put_unaligned64 > for wwn access")) that each try to sidestep distinct problems with gcc > behavior (code growth and increased stack usage). Unfortunately after > both have been applied, a more serious gcc bug has been uncovered, leading > to incorrect object code that discards part of a function and causes > undefined behavior. > > As part of this problem is how __builtin_constant_p gets evaluated on an > argument passed by reference into an inline function, this avoids the use > of __builtin_constant_p() for all architectures that set > CONFIG_ARCH_USE_BUILTIN_BSWAP. Most architectures do not set > ARCH_SUPPORTS_OPTIMIZED_INLINING, which means they probably do not suffer > from the problem in the qla2xxx driver, but they might still run into it > elsewhere. > > Both of the original workarounds were only merged in the 4.6 kernel, and > the bug that is fixed by this patch should only appear if both are there, > so we probably don't need to backport the fix. On the other hand, it > works by simplifying the code path and should not have any negative > effects. > > [arnd@arndb.de: fix older gcc warnings] > (http://lkml.kernel.org/r/12243652.bxSxEgjgfk@wuerfel) > Link: https://lkml.org/lkml/headers/2016/4/12/1103 > Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66122 > Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70232 > Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646 > Fixes: e3bde9568d99 ("include/linux/unaligned: force inlining of byteswap operations") > Fixes: ef3fb2422ffe ("scsi: fc: use get/put_unaligned64 for wwn access") > Link: http://lkml.kernel.org/r/1780465.XdtPJpi8Tt@wuerfel > Signed-off-by: Arnd Bergmann > Reviewed-by: Josh Poimboeuf > Tested-by: Josh Poimboeuf # on gcc-5.3 > Tested-by: Quinn Tran > Cc: Martin Jambor > Cc: "Martin K. Petersen" > Cc: James Bottomley > Cc: Denys Vlasenko > Cc: Thomas Graf > Cc: Peter Zijlstra > Cc: David Rientjes > Cc: Ingo Molnar > Cc: Himanshu Madhani > Cc: Jan Hubicka > Signed-off-by: Andrew Morton This became commit 7322dd755e7d ("byteswap: try to avoid __builtin_constant_p gcc bug"). That commit was included in v4.6-rc7. Ever since that rc I see this warning when building for x86_64: net/netfilter/ipvs/ip_vs_sync.c: In function ‘ip_vs_proc_sync_conn’: net/netfilter/ipvs/ip_vs_sync.c:1069:33: warning: ‘opt.init_seq’ may be used uninitialized in this function [-Wmaybe-uninitialized] struct ip_vs_sync_conn_options opt; ^ net/netfilter/ipvs/ip_vs_sync.c:1069:33: warning: ‘opt.delta’ may be used uninitialized in this function [-Wmaybe-uninitialized] net/netfilter/ipvs/ip_vs_sync.c:1069:33: warning: ‘opt.previous_delta’ may be used uninitialized in this function [-Wmaybe-uninitialized] net/netfilter/ipvs/ip_vs_sync.c:1069:33: warning: ‘*((void *)&opt+12).init_seq’ may be used uninitialized in this function [-Wmaybe-uninitialized] net/netfilter/ipvs/ip_vs_sync.c:1069:33: warning: ‘*((void *)&opt+12).delta’ may be used uninitialized in this function [-Wmaybe-uninitialized] net/netfilter/ipvs/ip_vs_sync.c:1069:33: warning: ‘*((void *)&opt+12).previous_delta’ may be used uninitialized in this function [-Wmaybe-uninitialized] (It doesn't show up when building for 32 bits x86. Perhaps there's an int/long mismatch somewhere in the related code.) Anyone else seeing this? It looks like a false positive. I can make it disappear by making sure ip_vs_proc_seqopt() isn't inlined. But that's not something I dare to put into a patch for a false positive. Anyone sitting on a better fix? Paul Bolle