x86: Save stack pointer in perf live regs savings

In order to prepare for fetching the stack pointer from the
regs when possible in dump_trace() instead of taking the
local one, save the current stack pointer in perf live regs saving.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>

arch/x86/include/asm/perf_event.h

@@ -152,6 +152,11 @@ extern unsigned long perf_misc_flags(struct pt_regs *regs);
 	(regs)->bp = caller_frame_pointer();			\
 	(regs)->cs = __KERNEL_CS;				\
 	regs->flags = 0;					\
+	asm volatile(						\
+		_ASM_MOV "%%"_ASM_SP ", %0\n"			\
+		: "=m" ((regs)->sp)				\
+		:: "memory"					\
+	);							\
 }
 
 #else