linux-kernel - [PATCH 5/7] x86: Use inline assembler instead of global register variable to get sp v2

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Date:	Tue, 22 Oct 2013 09:07:57 -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 5/7] x86: Use inline assembler instead of global register variable to get sp v2

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 with
a mov instead.

This also helps LLVM/clang, who do not support global register
variables.

v2: More general asm constraint. Fix description (Jan Beulich)
Cc: x86@...nel.org
Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
 arch/x86/include/asm/thread_info.h | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 2781119..ffda484 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -166,9 +166,11 @@ 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" : "=g" (sp));	\
+	sp;					\
+})
 
 /* how to get the thread information struct from C */
 static inline struct thread_info *current_thread_info(void)
-- 
1.8.3.1

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