linux-kernel - [PATCH] arm: LLVMLinux: Calculate current_thread

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Date:	Fri,  6 Sep 2013 17:47:40 -0400
From:	behanw@...verseincode.com
To:	linux@....linux.org.uk
Cc:	behanw@...verseincode.com, Mark Charlebois <charlebm@...il.com>,
	Will Deacon <will.deacon@....com>,
	Wade Farnsworth <wade_farnsworth@...tor.com>,
	Will Drewry <wad@...omium.org>,
	linux-arm-kernel@...ts.infradead.org (moderated list:ARM PORT),
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] arm: LLVMLinux: Calculate current_thread_info from fp

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

Use the frame pointer to calculate the start of the stack for current_thread_info()
The existing code uses the stack pointer to do this calculation.
Using the frame pointer yeilds the same value in a portable way.
This change supports being able to compile the kernel with gcc and Clang.

Signed-off-by: Mark Charlebois <charlebm@...il.com>
Signed-off-by: Behan Webster <behanw@...verseincode.com>
Reviewed-by: Jan-Simon Möller <dl9pf@....de>
---
 arch/arm/include/asm/thread_info.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
index df5e13d..cb50933 100644
--- a/arch/arm/include/asm/thread_info.h
+++ b/arch/arm/include/asm/thread_info.h
@@ -106,8 +106,9 @@ static inline struct thread_info *current_thread_info(void) __attribute_const__;
 
 static inline struct thread_info *current_thread_info(void)
 {
-	register unsigned long sp asm ("sp");
-	return (struct thread_info *)(sp & ~(THREAD_SIZE - 1));
+	return (struct thread_info *)
+		((u32)(__builtin_frame_address(0))
+		& ~(THREAD_SIZE - 1));
 }
 
 #define thread_saved_pc(tsk)	\
-- 
1.8.1.2

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