linux-kernel - [PATCH 48/74] x86, lto: Use inline assembler instead of global register variable to get sp

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Date:	Sat, 18 Aug 2012 19:56:44 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	linux-kernel@...r.kernel.org
Cc:	x86@...nel.org, mmarek@...e.cz, linux-kbuild@...r.kernel.org,
	JBeulich@...e.com, akpm@...ux-foundation.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH 48/74] x86, lto: Use inline assembler instead of global register variable to get sp

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

LTO in gcc 4.6/47. has trouble with global register variables. They were used
to read the stack pointer. Use a simple inline assembler statement instead.

I verified this generates the same binary (on 64bit) as the original
register variable.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
 arch/x86/include/asm/thread_info.h |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 89f794f..d9fbfa1 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -167,9 +167,11 @@ struct thread_info {
  */
 #ifndef __ASSEMBLY__
 
-
-/* how to get the current stack pointer from C */
-register unsigned long current_stack_pointer asm("esp") __used;
+#define current_stack_pointer ({ 		\
+	unsigned long sp;			\
+	asm("mov %%esp,%0" : "=r" (sp));	\
+	sp;					\
+})
 
 /* how to get the thread information struct from C */
 static inline struct thread_info *current_thread_info(void)
-- 
1.7.7.6

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