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Subject[PATCH] x86: redo "x86: Use inline assembler to get sp"
Date
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@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Mathias Krause <minipli@googlemail.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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