linux-kernel - [PATCH] x86: Fix AMD K6 indirect call check v2

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Message-Id: <1366562995-20530-1-git-send-email-andi@firstfloor.org>
Date:	Sun, 21 Apr 2013 09:49:55 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	x86@...nel.org
Cc:	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH] x86: Fix AMD K6 indirect call check v2

From: Andi Kleen <ak@...ux.intel.com>

The AMD K6 errata check relies on timing a indirect call.
But the way it was written it could be optimized to a direct call.
Force gcc to actually do a indirect call and not just
constant resolve the target address.

Found during code review, no runtime testing due to lack
of hardware.

v2: More description
Signed-off-by: Andi Kleen <ak@...ux.intel.com>

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 4a549db..11ea6f6 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -115,7 +115,7 @@ static void __cpuinit init_amd_k6(struct cpuinfo_x86 *c)
 		 */
 
 		n = K6_BUG_LOOP;
-		f_vide = vide;
+		asm("" : "=g" (f_vide) : "0" (vide));
 		rdtscl(d);
 		while (n--)
 			f_vide();
--
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