linux-kernel - [PATCH] x86: fdiv bug detection fix

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Date:	Thu, 31 Jul 2008 23:43:44 +0200
From:	Krzysztof Helt <krzysztof.h1@...pl>
To:	hpa@...or.com
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] x86: fdiv bug detection fix

From: Krzysztof Helt <krzysztof.h1@...pl>

The fdiv detection code writes s32 integer into
the boot_cpu_data.fdiv_bug. 
However, the boot_cpu_data.fdiv_bug is only char (s8)
field so the detection overwrites already set fields for
other bugs, e.g. the f00f bug field.

Use local s32 variable to receive result.

Signed-off-by: Krzysztof Helt <krzysztof.h1@...pl>
---

This is a partial fix to Bugzilla #9928  - fixes wrong 
information about the f00f bug (tested) and probably
for coma bug (I have no cpu to test this).

diff -urp linux-alsa/arch/x86/kernel/cpu/bugs.c linux-new/arch/x86/kernel/cpu/bugs.c
--- linux-alsa/arch/x86/kernel/cpu/bugs.c	2008-07-31 12:40:31.000000000 +0200
+++ linux-new/arch/x86/kernel/cpu/bugs.c	2008-07-31 23:24:07.722657435 +0200
@@ -50,6 +50,8 @@ static double __initdata y = 3145727.0;
  */
 static void __init check_fpu(void)
 {
+	s32 fdiv_bug;
+
 	if (!boot_cpu_data.hard_math) {
 #ifndef CONFIG_MATH_EMULATION
 		printk(KERN_EMERG "No coprocessor found and no math emulation present.\n");
@@ -74,8 +76,10 @@ static void __init check_fpu(void)
 		"fistpl %0\n\t"
 		"fwait\n\t"
 		"fninit"
-		: "=m" (*&boot_cpu_data.fdiv_bug)
+		: "=m" (*&fdiv_bug)
 		: "m" (*&x), "m" (*&y));
+
+	boot_cpu_data.fdiv_bug = fdiv_bug;
 	if (boot_cpu_data.fdiv_bug)
 		printk("Hmm, FPU with FDIV bug.\n");
 }
--
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