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

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Message-ID: <ce4ff595-f9d1-4c17-b68e-82739b07ad3e@email.android.com>
Date:	Wed, 27 Oct 2010 15:21:55 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jason Baron <jbaron@...hat.com>, rostedt@...dmis.org, mingo@...e.hu
CC:	mathieu.desnoyers@...ymtl.ca, tglx@...utronix.de,
	andi@...stfloor.org, roland@...hat.com, rth@...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

Could you detail the bug, please?  static_cpu_has() also uses asm goto.

"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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