linux-kernel - [PATCH] x86-64: Prevent gcc from optimizing away venosys

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Message-ID: <2060873692.1232.1307114423575.JavaMail.root@zmail05.collab.prod.int.phx2.redhat.com>
Date:	Fri, 3 Jun 2011 11:20:23 -0400 (EDT)
From:	Dave Anderson <anderson@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, andi@...stfloor.org, jstancek@...hat.com,
	anderson@...hat.com
Subject: [PATCH] x86-64: Prevent gcc from optimizing away venosys_1()

One of the changes in commit a4928cffe6435caf427ae673131a633c1329dbf3 
made the venosys_1() system call static, which causes it to be 
optimized out of the kernel:

  Author: Ingo Molnar <mingo@...e.hu>
  Date:   Wed Apr 23 13:20:56 2008 +0200

  "make namespacecheck" fixes

  Signed-off-by: Ingo Molnar <mingo@...e.hu>

Commit 2e8ad43ec07545780ce7992cb18e2d82c7abd24c had originally
changed all vsyscalls from being static for the same reason:

  Author: Andi Kleen <ak@...e.de>
  Date:   Mon Sep 12 18:49:24 2005 +0200

  [PATCH] x86-64: Prevent gcc 4 from optimizing away vsyscalls
    
  They were previously static.
    
  Signed-off-by: Andi Kleen <ak@...e.de>
  Signed-off-by: Linus Torvalds <torvalds@...l.org>

Reported-by: Jan Stancek <jstancek@...hat.com>
Signed-off-by: Dave Anderson <anderson@...hat.com>

---

diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index 3e68218..60a34af 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -222,7 +222,7 @@ vgetcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache)
 	return 0;
 }
 
-static long __vsyscall(3) venosys_1(void)
+long __vsyscall(3) venosys_1(void)
 {
 	return -ENOSYS;
 }
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