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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Steven Noonan <steven@uplinklabs.net>
Cc: Ingo Molnar <mingo@kernel.org>,
	Linux Kernel mailing List <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Jakub Jelinek <jakub@redhat.com>, Oleg Nesterov <oleg@redhat.com>,
	Fengguang Wu <fengguang.wu@intel.com>,
	Richard Henderson <rth@twiddle.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [GIT PULL] compiler/gcc4: Add quirk for 'asm goto' miscompilation bug
Date: Wed, 12 Feb 2014 20:11:49 -0800	[thread overview]
Message-ID: <CA+55aFys_VK+q3LMRzEM-AKU-=fM_tgiDdLm2AO=jVfH7OvrHQ@mail.gmail.com> (raw)
In-Reply-To: <CAKbGBLgs9t4HPD4duBt=vPaw0WfxLv5qr6pNupHsPTFaV5m+dQ@mail.gmail.com>

On Wed, Feb 12, 2014 at 7:09 PM, Steven Noonan <steven@uplinklabs.net> wrote:
>
> If I change the GCC_VERSION check for the asm_volatile_goto quirk to
> include 4.8.2, then KVM guests are properly cleaned up.

Ok, I guess that means we should just make the quirk unconditional.

Ingo, do you want to do that or should I?

> So is there some other 'asm goto' bug we haven't yet fully uncovered
> and reported to GCC upstream?

Not to my knowledge. But I'm sure Jakub&co would love to have a test-case.

Sadly, gcc has that really annoying habit of making small changes
create *huge* changes in label numbers etc, and that's definitely the
case with the extra empty asm - it's basically impossible to compare
the generated asm with and without the workaround, because all the
label numbers change.

I have no idea how gcc people debug things like this, when the output
is so unstable.

Jakub, any suggestions to how Steven might be able to pinpoint where
the code generation problem lies?

                Linus

  reply	other threads:[~2014-02-13  4:11 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-10-12 17:10 Ingo Molnar
2014-02-13  3:09 ` Steven Noonan
2014-02-13  4:11   ` Linus Torvalds [this message]
2014-02-13  4:53     ` [PATCH] compiler/gcc4: make quirk for asm_volatile_goto unconditional Steven Noonan
2014-02-13  6:48       ` Mike Galbraith
2014-02-13  7:01         ` [PATCH v2] " Steven Noonan
2014-02-13 11:37           ` [tip:x86/urgent] compiler/gcc4: Make quirk for asm_volatile_goto( ) unconditional tip-bot for Steven Noonan
2014-02-13 11:55             ` Jakub Jelinek
2014-02-13 13:44               ` Steven Noonan
2014-07-10 15:00               ` Vlastimil Babka
2014-02-13  7:48     ` [GIT PULL] compiler/gcc4: Add quirk for 'asm goto' miscompilation bug Jakub Jelinek
2014-02-13  9:43     ` Ingo Molnar

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