linux-kernel - Re: [PATCH 2/2] jump label: disable due to compiler bug

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Date:	Thu, 28 Oct 2010 10:17:57 -0400
From:	Jason Baron <jbaron@...hat.com>, rth@...hat.com
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	rostedt@...dmis.org, mingo@...e.hu, mathieu.desnoyers@...ymtl.ca,
	tglx@...utronix.de, andi@...stfloor.org, roland@...hat.com,
	masami.hiramatsu.pt@...achi.com, fweisbec@...il.com,
	avi@...hat.com, davem@...emloft.net, vgoyal@...hat.com,
	sam@...nborg.org, tony@...eyournoodle.com,
	ddaney@...iumnetworks.com, dsd@...top.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] jump label: disable due to compiler bug

On Wed, Oct 27, 2010 at 03:21:55PM -0700, H. Peter Anvin wrote:
> Could you detail the bug, please?  static_cpu_has() also uses asm goto.
> 

It seems that gcc can leave the stack in an inconsistent state.

I only saw this in the 'jmp' enabled case, I'm not sure if it can occur in the
straight-line code path as well.

thanks,

-Jason

> "Jason Baron" <jbaron@...hat.com> wrote:
> 
> >Unfortunately, we found a compiler bug in the implementation of
> >'asm goto'. The bug can cause the kernel to crash.
> >
> >For now, we are disabling jump labels with a big hammer. When the
> >gcc fix is committed, we will update the kernel with a better check
> >for either the version number it's fix in, or some detection of
> >whether gcc has the fix in place.
> >
> >Signed-off-by: Jason Baron <jbaron@...hat.com>
> >---
> > include/linux/jump_label.h |    9 +++++++++
> > 1 files changed, 9 insertions(+), 0 deletions(-)
> >
> >diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
> >index b67cb18..954462a 100644
> >--- a/include/linux/jump_label.h
> >+++ b/include/linux/jump_label.h
> >@@ -1,11 +1,20 @@
> > #ifndef _LINUX_JUMP_LABEL_H
> > #define _LINUX_JUMP_LABEL_H
> > 
> >+/*
> >+ * A compiler bug was found in the implementation of 'asm goto'. Thus,
> >+ * we are disabling it for now pending a better check for compiler
> >version
> >+ * that fixes it.
> >+ */
> >+#if 0
> >+
> > #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_HAVE_ARCH_JUMP_LABEL)
> > # include <asm/jump_label.h>
> > # define HAVE_JUMP_LABEL
> > #endif
> > 
> >+#endif
> >+
> > enum jump_label_type {
> > 	JUMP_LABEL_ENABLE,
> > 	JUMP_LABEL_DISABLE
> >-- 
> >1.7.1
> 
> -- 
> Sent from my mobile phone.  Please pardon any lack of formatting.
--
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