From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>, Thomas Graf <tgraf@suug.ch>,
Peter Zijlstra <peterz@infradead.org>,
David Rientjes <rientjes@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
James Bottomley <James.Bottomley@HansenPartnership.com>
Subject: Re: This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations)
Date: Wed, 13 Apr 2016 10:15:00 -0500 [thread overview]
Message-ID: <20160413151500.tate3u6trg4agugo@treble> (raw)
In-Reply-To: <20160413123607.3y3v5esq3myto4kc@treble>
On Wed, Apr 13, 2016 at 07:36:07AM -0500, Josh Poimboeuf wrote:
> On Wed, Apr 13, 2016 at 02:12:25PM +0200, Denys Vlasenko wrote:
> > 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:
> > >>
> > >> <get_unaligned_be16> (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 <dvlasenk@redhat.com>
> > >> Cc: Ingo Molnar <mingo@kernel.org>
> > >> Cc: Thomas Graf <tgraf@suug.ch>
> > >> Cc: Peter Zijlstra <peterz@infradead.org>
> > >> Cc: David Rientjes <rientjes@google.com>
> > >> Cc: Andrew Morton <akpm@linux-foundation.org>
> > >> 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 <qla2x00_get_host_fabric_name>:
> > > 2f53: 55 push %rbp
> > > 2f54: 48 89 e5 mov %rsp,%rbp
> > >
> > > 0000000000002f57 <qla2x00_get_fc_host_stats>:
> > > 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.
>
> Makes sense in theory, but the bug doesn't actually trigger when I
> revert the patch and set CONFIG_OPTIMIZE_INLINING=n.
>
> Perhaps even more surprising, it doesn't trigger *with* the patch and
> CONFIG_OPTIMIZE_INLINING=n.
[ Adding James to CC since this bug affects scsi. ]
Here's the gcc bug:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646
--
Josh
next prev parent reply other threads:[~2016-04-13 15:15 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-04 19:45 [PATCH] asm-generic: force inlining of some atomic_long operations Denys Vlasenko
2016-02-04 19:45 ` [PATCH] force inlining of some byteswap operations Denys Vlasenko
2016-02-05 7:28 ` Ingo Molnar
2016-04-13 3:36 ` This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations) Josh Poimboeuf
2016-04-13 12:12 ` Denys Vlasenko
2016-04-13 12:36 ` Josh Poimboeuf
2016-04-13 15:15 ` Josh Poimboeuf [this message]
2016-04-13 16:55 ` James Bottomley
2016-04-13 17:10 ` Josh Poimboeuf
2016-04-14 15:29 ` Denys Vlasenko
2016-04-14 15:57 ` Josh Poimboeuf
2016-04-14 17:09 ` Denys Vlasenko
2016-04-15 5:45 ` Ingo Molnar
2016-04-15 13:47 ` Josh Poimboeuf
2016-04-15 22:20 ` Josh Poimboeuf
2016-04-16 9:03 ` Ingo Molnar
2016-04-18 13:39 ` Josh Poimboeuf
2016-04-18 14:07 ` Arnd Bergmann
2016-04-18 14:12 ` Josh Poimboeuf
2016-04-18 14:21 ` Arnd Bergmann
2016-04-19 8:52 ` Ingo Molnar
2016-04-19 13:56 ` [PATCH] scsi: fc: force inlining of wwn conversion functions Josh Poimboeuf
2016-04-22 23:17 ` Quinn Tran
2016-04-25 16:07 ` Josh Poimboeuf
2016-04-26 2:40 ` Martin K. Petersen
2016-04-26 3:37 ` James Bottomley
2016-04-26 7:22 ` Arnd Bergmann
2016-04-26 8:35 ` Christoph Hellwig
2016-04-26 10:05 ` Arnd Bergmann
2016-04-26 13:06 ` Martin K. Petersen
2016-04-26 15:58 ` Arnd Bergmann
2016-04-26 22:36 ` James Bottomley
2016-04-27 0:44 ` Martin K. Petersen
2016-04-27 11:05 ` Martin Jambor
2016-04-27 21:34 ` Arnd Bergmann
2016-04-28 14:58 ` Chris Metcalf
2016-04-28 15:23 ` Arnd Bergmann
2016-04-28 15:48 ` Chris Metcalf
2016-04-27 22:00 ` [PATCH, RFT] byteswap: try to avoid __builtin_constant_p gcc bug Arnd Bergmann
2016-04-27 22:11 ` Josh Poimboeuf
2016-04-28 16:27 ` Quinn Tran
2016-04-16 7:42 ` This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations) Arnd Bergmann
2016-04-18 13:22 ` Josh Poimboeuf
2016-02-04 19:45 ` [PATCH] force inlining of unaligned byteswap operations Denys Vlasenko
2016-02-05 7:28 ` Ingo Molnar
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