linux-kernel - [PATCH] x86: LLVMLinux: Reimplement current_stack

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Date:	Thu, 20 Feb 2014 20:44:42 -0800
From:	behanw@...verseincode.com
To:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, peterz@...radead.org, ak@...ux.intel.com,
	oleg@...hat.com
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Behan Webster <behanw@...verseincode.com>
Subject: [PATCH] x86: LLVMLinux: Reimplement current_stack_pointer without register usage.

From: Behan Webster <behanw@...verseincode.com>

Use asm to make the globally named register work again for gcc and clang.
Much more efficient than copying the stack pointer to a variable and back again.

Signed-off-by: Behan Webster <behanw@...verseincode.com>
---
 arch/x86/include/asm/thread_info.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index e1940c0..e27ccc1 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -163,10 +163,10 @@ struct thread_info {
  */
 #ifndef __ASSEMBLY__
 
-#define current_stack_pointer ({		\
-	unsigned long sp;			\
-	asm("mov %%esp,%0" : "=g" (sp));	\
-	sp;					\
+#define current_stack_pointer ({			\
+	register unsigned long sp asm("esp") __used;	\
+	asm("" : "=r" (sp));				\
+	sp;						\
 })
 
 /* how to get the thread information struct from C */
-- 
1.8.3.2

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