From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Denys Vlasenko <dvlasenk@redhat.com>,
James Bottomley <James.Bottomley@HansenPartnership.com>,
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>,
linux-scsi <linux-scsi@vger.kernel.org>,
jamborm@gcc.gnu.org
Subject: Re: This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations)
Date: Fri, 15 Apr 2016 17:20:37 -0500 [thread overview]
Message-ID: <20160415222037.wu4n6w2yedxdzfle@treble> (raw)
In-Reply-To: <20160415134745.wxb73xemv2tqib5m@treble>
On Fri, Apr 15, 2016 at 08:47:45AM -0500, Josh Poimboeuf wrote:
> On Fri, Apr 15, 2016 at 07:45:19AM +0200, Ingo Molnar wrote:
> >
> > * Denys Vlasenko <dvlasenk@redhat.com> wrote:
> >
> > > > In fact, the following patch seems to fix it:
> > > >
> > > > diff --git a/include/scsi/scsi_transport_fc.h b/include/scsi/scsi_transport_fc.h
> > > > index bf66ea6..56b9e81 100644
> > > > --- a/include/scsi/scsi_transport_fc.h
> > > > +++ b/include/scsi/scsi_transport_fc.h
> > > > @@ -796,7 +796,7 @@ fc_remote_port_chkready(struct fc_rport *rport)
> > > > return result;
> > > > }
> > > >
> > > > -static inline u64 wwn_to_u64(u8 *wwn)
> > > > +static __always_inline u64 wwn_to_u64(u8 *wwn)
> > > > {
> > > > return get_unaligned_be64(wwn);
> > > > }
> > >
> > > It is not a guarantee.
> >
> > Of course it's a workaround - but is there any deterministic way to turn off this
> > GCC bug (by activating some GCC command line switch), or do we have to live with
> > objtool warning about this GCC?
>
> I don't think we know yet if there's a reliable way to turn the bug off.
>
> Also, according to the gcc guys, this bug won't always result in a
> truncated function, and may sometimes just make some inline function
> call sites disappear:
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646#c14
>
> though I haven't been able to confirm that experimentally. But if it's
> true, that means that objtool won't be able to detect all cases of the
> bug and some function calls may just silently disappear!
>
> There's a lot of activity in the bug now, so hopefully they'll be able
> to tell us soon if there's a reliable way to avoid it and/or detect it.
>
> BTW, Denys posted a workaround patch for the qla2xxxx code:
>
> https://lkml.kernel.org/r/1460716583-15673-1-git-send-email-dvlasenk@redhat.com
Martin Jambor wrote a succinct summary of the conditions needed for this
bug:
"This bug can occur when an inlineable function containing a call to
__builtin_constant_p, which checks a parameter or a value it
references and a (possibly indirect) caller of the function actually
passes a constant, but stores it using a type of a different size."
So to prevent it from happening elsewhere in the kernel, it sounds like
we'd have to either remove all uses of __builtin_constant_p() or disable
inlining completely.
There's also no reliable way to detect the bug has occurred, though
objtool will detect it in cases when the function gets truncated.
--
Josh
next prev parent reply other threads:[~2016-04-15 22:20 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
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 [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20160415222037.wu4n6w2yedxdzfle@treble \
--to=jpoimboe@redhat.com \
--cc=James.Bottomley@HansenPartnership.com \
--cc=akpm@linux-foundation.org \
--cc=arnd@arndb.de \
--cc=dvlasenk@redhat.com \
--cc=jamborm@gcc.gnu.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-scsi@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=rientjes@google.com \
--cc=tgraf@suug.ch \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).