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Subject[PATCH 4.4 05/53] x86/asm: Use register variable to get stack pointer value
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andrey Ryabinin <aryabinin@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 <aryabinin@virtuozzo.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170929141537.29167-1-aryabinin@virtuozzo.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[dwmw2: We want ASM_CALL_CONSTRAINT for retpoline]
Signed-off-by: David Woodhouse <dwmw@amazon.co.ku>
Signed-off-by: Razvan Ghitulete <rga@amazon.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/include/asm/asm.h | 11 +++++++++++
arch/x86/include/asm/thread_info.h | 11 -----------
arch/x86/kernel/irq_32.c | 6 +++---
arch/x86/kernel/traps.c | 2 +-
4 files changed, 15 insertions(+), 15 deletions(-)

--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -105,4 +105,15 @@
/* For C file, we already have NOKPROBE_SYMBOL macro */
#endif

+#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
+
#endif /* _ASM_X86_ASM_H */
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -166,17 +166,6 @@ static inline struct thread_info *curren
return (struct thread_info *)(current_top_of_stack() - THREAD_SIZE);
}

-static inline unsigned long current_stack_pointer(void)
-{
- unsigned long sp;
-#ifdef CONFIG_X86_64
- asm("mov %%rsp,%0" : "=g" (sp));
-#else
- asm("mov %%esp,%0" : "=g" (sp));
-#endif
- return sp;
-}
-
#else /* !__ASSEMBLY__ */

#ifdef CONFIG_X86_64
--- a/arch/x86/kernel/irq_32.c
+++ b/arch/x86/kernel/irq_32.c
@@ -65,7 +65,7 @@ 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 execute_on_irq_stack(int overflow, struct irq_desc *desc)
@@ -89,7 +89,7 @@ static inline int execute_on_irq_stack(i

/* 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);
@@ -142,7 +142,7 @@ 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);
}
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -166,7 +166,7 @@ void ist_begin_non_atomic(struct pt_regs
* from double_fault.
*/
BUG_ON((unsigned long)(current_top_of_stack() -
- current_stack_pointer()) >= THREAD_SIZE);
+ current_stack_pointer) >= THREAD_SIZE);

preempt_enable_no_resched();
}

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