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Groups > linux.kernel > #1377890
| From | Josh Poimboeuf <jpoimboe@redhat.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 14:40 +0200 |
| Message-ID | <rnsfp-1e6-25@gated-at.bofh.it> (permalink) |
| References | <qYy4G-6oS-19@gated-at.bofh.it> <qYy4H-6oS-27@gated-at.bofh.it> <rnjOO-2xX-11@gated-at.bofh.it> <rnrW2-15F-15@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
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.
--
Josh
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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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