linux-kernel - [PATCH] x86: redo "x86: Use inline assembler to get sp"

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Message-Id: <1394178752-18047-1-git-send-email-minipli@googlemail.com>
Date:	Fri,  7 Mar 2014 08:52:32 +0100
From:	Mathias Krause <minipli@...glemail.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	Mathias Krause <minipli@...glemail.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Brian Gerst <brgerst@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andi Kleen <ak@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: [PATCH] x86: redo "x86: Use inline assembler to get sp"

This patch restores the changes of commit dff38e3e93 "x86: Use inline
assembler instead of global register variable to get sp". They got lost
in commit 198d208df4 "x86: Keep thread_info on thread stack in x86_32"
while moving the code to arch/x86/kernel/irq_32.c.

Quoting Andi from commit dff38e3e93:

"""
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, which does not support global register
variables.
"""

Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: H. Peter Anvin <hpa@...ux.intel.com>
Signed-off-by: Mathias Krause <minipli@...glemail.com>
---

If it's not obvious, this patch should be applied to tip.git on top of
tip/x86/threadinfo.

 arch/x86/kernel/irq_32.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/irq_32.c b/arch/x86/kernel/irq_32.c
index 988dc8bcae..63ce838e5a 100644
--- a/arch/x86/kernel/irq_32.c
+++ b/arch/x86/kernel/irq_32.c
@@ -70,7 +70,11 @@ static void call_on_stack(void *func, void *stack)
 }
 
 /* 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;					\
+})
 
 static inline void *current_stack(void)
 {
-- 
1.7.10.4

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