3.16.56-rc1 review patch.  If anyone has any objections, please let me know.


From: Andrey Ryabinin <aryabi...@virtuozzo.com>

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 <aryabi...@virtuozzo.com>
Reviewed-by: Josh Poimboeuf <jpoim...@redhat.com>
Cc: Andy Lutomirski <l...@kernel.org>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Link: http://lkml.kernel.org/r/20170929141537.29167-1-aryabi...@virtuozzo.com
Signed-off-by: Ingo Molnar <mi...@kernel.org>
[dwmw2: We want ASM_CALL_CONSTRAINT for retpoline]
Signed-off-by: David Woodhouse <d...@amazon.co.ku>
Signed-off-by: Razvan Ghitulete <r...@amazon.de>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
[bwh: Backported to 3.16: drop change in ist_begin_non_atomic()]
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -80,4 +80,15 @@
 /* For C file, we already have NOKPROBE_SYMBOL macro */
+#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
@@ -170,17 +170,6 @@ static inline struct thread_info *curren
        return ti;
-static inline unsigned long current_stack_pointer(void)
-       unsigned long sp;
-#ifdef CONFIG_X86_64
-       asm("mov %%rsp,%0" : "=g" (sp));
-       asm("mov %%esp,%0" : "=g" (sp));
-       return sp;
 #else /* !__ASSEMBLY__ */
 /* how to get the thread information struct from ASM */
--- a/arch/x86/kernel/irq_32.c
+++ b/arch/x86/kernel/irq_32.c
@@ -71,7 +71,7 @@ static void call_on_stack(void *func, vo
 static inline void *current_stack(void)
-       return (void *)(current_stack_pointer() & ~(THREAD_SIZE - 1));
+       return (void *)(current_stack_pointer & ~(THREAD_SIZE - 1));
 static inline int
@@ -96,7 +96,7 @@ execute_on_irq_stack(int overflow, struc
        /* Save the next esp at the bottom of the stack */
        prev_esp = (u32 *)irqstk;
-       *prev_esp = current_stack_pointer();
+       *prev_esp = current_stack_pointer;
        if (unlikely(overflow))
                call_on_stack(print_stack_overflow, isp);
@@ -149,7 +149,7 @@ void do_softirq_own_stack(void)
        /* Push the previous esp onto the stack */
        prev_esp = (u32 *)irqstk;
-       *prev_esp = current_stack_pointer();
+       *prev_esp = current_stack_pointer;
        call_on_stack(__do_softirq, isp);

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