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Groups > linux.kernel > #1378101
| From | James Bottomley <James.Bottomley@HansenPartnership.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations) |
| Date | 2016-04-13 19:00 +0200 |
| Message-ID | <rnwiZ-4a7-1@gated-at.bofh.it> (permalink) |
| References | (1 earlier) <qYy4H-6oS-27@gated-at.bofh.it> <rnjOO-2xX-11@gated-at.bofh.it> <rnrW2-15F-15@gated-at.bofh.it> <rnsfp-1e6-25@gated-at.bofh.it> <rnuKd-3cP-7@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Wed, 2016-04-13 at 10:15 -0500, Josh Poimboeuf wrote:
> 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_O
> > > > > s,
> > > > > 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
>
Actually, adding me doesn't help, I've added linux-scsi. The summary
is that there's a but in gcc-5.3.1 which is miscompiling qla_attr.c ...
this means we're going to have to ask the compiler version of reported
crashes.
James
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This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations) Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-13 05:40 +0200
Re: This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations) Denys Vlasenko <dvlasenk@redhat.com> - 2016-04-13 14:20 +0200
Re: This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations) Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-13 14:40 +0200
Re: This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations) Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-13 17:20 +0200
Re: This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations) James Bottomley <James.Bottomley@HansenPartnership.com> - 2016-04-13 19:00 +0200
Re: This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations) Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-13 19:20 +0200
Re: This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations) Denys Vlasenko <dvlasenk@redhat.com> - 2016-04-14 17:30 +0200
Re: This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations) Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-14 18:00 +0200
Re: This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations) Denys Vlasenko <dvlasenk@redhat.com> - 2016-04-14 19:10 +0200
Re: This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations) Ingo Molnar <mingo@kernel.org> - 2016-04-15 07:50 +0200
Re: This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations) Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-15 15:50 +0200
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