Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758021AbcDMMMa (ORCPT ); Wed, 13 Apr 2016 08:12:30 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56482 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751074AbcDMMM2 (ORCPT ); Wed, 13 Apr 2016 08:12:28 -0400 Message-ID: <570E37A9.2050503@redhat.com> Date: Wed, 13 Apr 2016 14:12:25 +0200 From: Denys Vlasenko User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Josh Poimboeuf CC: Ingo Molnar , Thomas Graf , Peter Zijlstra , David Rientjes , Andrew Morton , linux-kernel@vger.kernel.org, Arnd Bergmann Subject: Re: This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations) References: <1454615136-32308-1-git-send-email-dvlasenk@redhat.com> <1454615136-32308-2-git-send-email-dvlasenk@redhat.com> <20160413033649.7r3msnmo3trtq47z@treble> In-Reply-To: <20160413033649.7r3msnmo3trtq47z@treble> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3418 Lines: 90 On 04/13/2016 05:36 AM, Josh Poimboeuf wrote: > On Thu, Feb 04, 2016 at 08:45:35PM +0100, Denys Vlasenko wrote: >> Sometimes gcc mysteriously doesn't inline >> very small functions we expect to be inlined. See >> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66122 >> >> With this .config: >> http://busybox.net/~vda/kernel_config_OPTIMIZE_INLINING_and_Os, >> the following functions get deinlined many times. >> Examples of disassembly: >> >> (12 copies, 51 calls): >> 66 8b 07 mov (%rdi),%ax >> 55 push %rbp >> 48 89 e5 mov %rsp,%rbp >> 86 e0 xchg %ah,%al >> 5d pop %rbp >> c3 retq ... >> This patch fixes this via s/inline/__always_inline/. >> Code size decrease after the patch is ~4.5k: >> >> text data bss dec hex filename >> 92202377 20826112 36417536 149446025 8e85d89 vmlinux >> 92197848 20826112 36417536 149441496 8e84bd8 vmlinux5_swap_after >> >> Signed-off-by: Denys Vlasenko >> Cc: Ingo Molnar >> Cc: Thomas Graf >> Cc: Peter Zijlstra >> Cc: David Rientjes >> Cc: Andrew Morton >> Cc: linux-kernel@vger.kernel.org >> --- >> include/uapi/linux/byteorder/big_endian.h | 24 ++++++++++++------------ >> include/uapi/linux/byteorder/little_endian.h | 24 ++++++++++++------------ >> include/uapi/linux/swab.h | 10 +++++----- >> 3 files changed, 29 insertions(+), 29 deletions(-) > > Hi, > > This patch seems to trigger a gcc bug which can produce corrupt code. I > discovered it when investigating an objtool warning reported by kbuild > bot: > > http://www.spinics.net/lists/linux-scsi/msg95481.html > > From the disassembly of drivers/scsi/qla2xxx/qla_attr.o: > > 0000000000002f53 : > 2f53: 55 push %rbp > 2f54: 48 89 e5 mov %rsp,%rbp > > 0000000000002f57 : > 2f57: 55 push %rbp > 2f58: b9 e8 00 00 00 mov $0xe8,%ecx > 2f5d: 48 89 e5 mov %rsp,%rbp > ... > > Note that qla2x00_get_host_fabric_name() is inexplicably truncated after > setting up the frame pointer. It falls through to the next function, which is > very wrong. Wow, that's ... interesting. > I can recreate it with either gcc 5.3.1 or gcc 6.0 on linus/master with > the .config from the above link. > > The call chain which appears to trigger the problem is: > > qla2x00_get_host_fabric_name() > wwn_to_u64() > get_unaligned_be64() > be64_to_cpup() > __be64_to_cpup() <- changed to __always_inline by this patch > > It occurs with the combination of the following two recent commits: > > - bc27fb68aaad ("include/uapi/linux/byteorder, swab: force inlining of some byteswap operations") > - ef3fb2422ffe ("scsi: fc: use get/put_unaligned64 for wwn access") > > I can confirm that reverting either patch makes the problem go away. > I'm planning on opening a gcc bug tomorrow. Note that if CONFIG_OPTIMIZE_INLINING is not set, _all_ "inline" keywords are in fact __always_inline, so the bug must be triggering even without the patch.