linux-kernel - 2.4.35.1 and panic at boot with arch=c3 and gcc-4.x

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Message-ID: <20070905220027.GB11602@1wt.eu>
Date:	Thu, 6 Sep 2007 00:00:27 +0200
From:	Willy Tarreau <w@....eu>
To:	Axel Reinhold <axel@...akout.de>,
	Richard Kojedzinszky <krichy@...etwork.hu>
Cc:	linux-kernel@...r.kernel.org
Subject: 2.4.35.1 and panic at boot with arch=c3 and gcc-4.x

Axel, Richard,

you both reported a very similar problem to me (panic at boot on VIA c3
with 2.4.35.1 when built with gcc-4.1). I could reproduce the problem
with your configs here and compare the code with your working builds.

I finally tracked the problem down to a dirty trick used to prevent
do_test_wp_bit() from being inlined (Axel, you identified the right
file). Unfortunately, this trick does not work anymore when gcc-4.x
is used without -fno-unit-at-a-time, so let's use the correct method
instead. I really hope that this trick is not used anywhere else!

The following patch fixes the issue for me. Could you please give it a
try before I merge it?

Thanks in advance,
Willy

--
>From 6ede67f873403d7e19fc0099952badd1db73ed66 Mon Sep 17 00:00:00 2001
From: Willy Tarreau <w@....eu>
Date: Wed, 5 Sep 2007 23:39:11 +0200
Subject: [PATCH] i386: do_test_wp_bit() must not be inlined

do_test_wp_bit() has a comment stating that it must not be inlined.
Unfortunately, the trick to prevent it from being inlined is not
reliable under gcc 4.x.

The simple fix consists in specifying the noinline attribute.
Tested and confirmed to produce the correct code for gcc versions
2.95.3, 3.3.6, 3.4.6, 4.0.2, 4.1.1 and 4.2.1.

Special thanks to Axel Reinhold and Richard Kojedzinszky for their
continuous feedback when trying to solve this issue.

Signed-off-by: Willy Tarreau <w@....eu>
---
 arch/i386/mm/init.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/i386/mm/init.c b/arch/i386/mm/init.c
index 0dc1751..2d81117 100644
--- a/arch/i386/mm/init.c
+++ b/arch/i386/mm/init.c
@@ -381,7 +381,7 @@ void __init paging_init(void)
  * This function cannot be __init, since exceptions don't work in that
  * section.
  */
-static int do_test_wp_bit(unsigned long vaddr);
+static int __attribute__((noinline)) do_test_wp_bit(unsigned long vaddr);

 void __init test_wp_bit(void)
 {
@@ -561,8 +561,8 @@ void __init mem_init(void)

 }

-/* Put this after the callers, so that it cannot be inlined */
-static int do_test_wp_bit(unsigned long vaddr)
+/* This function must not be inlined */
+static int __attribute__((noinline)) do_test_wp_bit(unsigned long vaddr)
 {
 	char tmp_reg;
 	int flag;
-- 
1.5.2.5

-
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