Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756962AbcDMDgz (ORCPT ); Tue, 12 Apr 2016 23:36:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38270 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756002AbcDMDgx (ORCPT ); Tue, 12 Apr 2016 23:36:53 -0400 Date: Tue, 12 Apr 2016 22:36:49 -0500 From: Josh Poimboeuf To: Denys Vlasenko Cc: Ingo Molnar , Thomas Graf , Peter Zijlstra , David Rientjes , Andrew Morton , linux-kernel@vger.kernel.org, Arnd Bergmann Subject: This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations) Message-ID: <20160413033649.7r3msnmo3trtq47z@treble> References: <1454615136-32308-1-git-send-email-dvlasenk@redhat.com> <1454615136-32308-2-git-send-email-dvlasenk@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1454615136-32308-2-git-send-email-dvlasenk@redhat.com> User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Wed, 13 Apr 2016 03:36:52 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5198 Lines: 138 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 > > (12 copies, 135 calls): > 8b 07 mov (%rdi),%eax > 55 push %rbp > 48 89 e5 mov %rsp,%rbp > 0f c8 bswap %eax > 5d pop %rbp > c3 retq > > (2 copies, 20 calls): > 48 8b 07 mov (%rdi),%rax > 55 push %rbp > 48 89 e5 mov %rsp,%rbp > 48 0f c8 bswap %rax > 5d pop %rbp > c3 retq > > <__swab16p> (16 copies, 146 calls): > 55 push %rbp > 89 f8 mov %edi,%eax > 86 e0 xchg %ah,%al > 48 89 e5 mov %rsp,%rbp > 5d pop %rbp > c3 retq > > <__swab32p> (43 copies, ~560 calls): > 55 push %rbp > 89 f8 mov %edi,%eax > 0f c8 bswap %eax > 48 89 e5 mov %rsp,%rbp > 5d pop %rbp > c3 retq > > <__swab64p> (21 copies, 119 calls): > 55 push %rbp > 48 89 f8 mov %rdi,%rax > 48 0f c8 bswap %rax > 48 89 e5 mov %rsp,%rbp > 5d pop %rbp > c3 retq > > <__swab32s> (6 copies, 47 calls): > 8b 07 mov (%rdi),%eax > 55 push %rbp > 48 89 e5 mov %rsp,%rbp > 0f c8 bswap %eax > 89 07 mov %eax,(%rdi) > 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. 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. > -static inline __u64 __be64_to_cpup(const __be64 *p) > +static __always_inline __u64 __be64_to_cpup(const __be64 *p) > { > return __swab64p((__u64 *)p); > } -- Josh