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Subject[PATCH 3.2 057/104] x86/asm: Use register variable to get stack pointer value
3.2.101-rc1 review patch.  If anyone has any objections, please let me know.


From: Andrey Ryabinin <>

commit 196bd485ee4f03ce4c690bfcf38138abfcd0a4bc upstream.

Currently we use current_stack_pointer() function to get the value
of the stack pointer register. Since commit:

f5caf621ee35 ("x86/asm: Fix inline asm call constraints for Clang")

... we have a stack register variable declared. It can be used instead of
current_stack_pointer() function which allows to optimize away some
excessive "mov %rsp, %<dst>" instructions:

-mov %rsp,%rdx
-sub %rdx,%rax
-cmp $0x3fff,%rax
-ja ffffffff810722fd <ist_begin_non_atomic+0x2d>

+sub %rsp,%rax
+cmp $0x3fff,%rax
+ja ffffffff810722fa <ist_begin_non_atomic+0x2a>

Remove current_stack_pointer(), rename __asm_call_sp to current_stack_pointer
and use it instead of the removed function.

Signed-off-by: Andrey Ryabinin <>
Reviewed-by: Josh Poimboeuf <>
Cc: Andy Lutomirski <>
Cc: Linus Torvalds <>
Cc: Peter Zijlstra <>
Cc: Thomas Gleixner <>
Signed-off-by: Ingo Molnar <>
[dwmw2: We want ASM_CALL_CONSTRAINT for retpoline]
Signed-off-by: David Woodhouse <>
Signed-off-by: Razvan Ghitulete <>
Signed-off-by: Greg Kroah-Hartman <>
[bwh: Backported to 3.2: current_stack_pointer was never changed to a function,
but was only defined for x86_32]
Signed-off-by: Ben Hutchings <>
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -59,4 +59,15 @@
" .previous\n"

+#ifndef __ASSEMBLY__
+ * This output constraint should be used for any inline asm which has a "call"
+ * instruction. Otherwise the asm may be inserted before the frame pointer
+ * gets set up by the containing function. If you forget to do this, objtool
+ * may print a "call without frame pointer save/setup" warning.
+ */
+register unsigned long current_stack_pointer asm(_ASM_SP);
+#define ASM_CALL_CONSTRAINT "+r" (current_stack_pointer)
#endif /* _ASM_X86_ASM_H */
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -181,9 +181,6 @@ struct thread_info {
#ifndef __ASSEMBLY__

-/* how to get the current stack pointer from C */
-register unsigned long current_stack_pointer asm("esp") __used;
/* how to get the thread information struct from C */
static inline struct thread_info *current_thread_info(void)
 \ /
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