linux-kernel - [PATCH] kbuild, sparseirq: work around GCC bug with _

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Message-ID: <20081226134218.GA1054@elte.hu>
Date:	Fri, 26 Dec 2008 14:42:18 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	Yinghai Lu <yinghai@...nel.org>,
	David Howells <dhowells@...hat.com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	mel@....ul.ie
Subject: [PATCH] kbuild, sparseirq: work around GCC bug with __weak aliases


* Ingo Molnar <mingo@...e.hu> wrote:

> > I recall David Howells had a similar issue with the bootparamter patch 
> > set. The workaround he used was to add a barrier(); call in the weak 
> > function to avoid the inline.
> 
> could we add some extra attribute to __weak that would have a similar 
> effect? Something like __attribute__((noinline)), or something silly 
> like __attribute__((deprecated)) - just to keep gcc from screwing up 
> __weak functions? Perhaps adding a section attribute would have a 
> similar effect? (putting weak definitions into an extra section is 
> probably helpful anyway)

I've applied the patch below to tip/irq/sparseirq - could someone with an 
affected GCC version please check whether this solves the crash?

	Ingo

------------------->
>From 0d41e654c877a0de441448ca2f63a72ed11c5d84 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@...e.hu>
Date: Fri, 26 Dec 2008 14:39:51 +0100
Subject: [PATCH] kbuild, sparseirq: work around GCC bug with __weak aliases

Impact: fix panic on null pointer with sparseirq

Certain versions of GCC inline the weak global functions.
Work it around by marking __weak functions as noinline.

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 include/linux/compiler-gcc.h |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 5c8351b..1ad72e6 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -41,11 +41,17 @@
 
 #define __deprecated			__attribute__((deprecated))
 #define __packed			__attribute__((packed))
-#define __weak				__attribute__((weak))
 #define __naked				__attribute__((naked))
 #define __noreturn			__attribute__((noreturn))
 
 /*
+ * Mark weak aliases also noinline, because some GCC versions
+ * incorrectly inline weak aliases (even when a non-weak variant
+ * is there) and thus cause crashes:
+ */
+#define __weak				__attribute__((weak)) noinline
+
+/*
  * From the GCC manual:
  *
  * Many functions have no effects except the return value and their
--
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