Commit 31679f38 authored by Andi Kleen's avatar Andi Kleen Committed by Andi Kleen
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[PATCH] Simplify profile_pc on x86-64 



Use knowledge about EFLAGS layout (bits 22:63 are always 0) to distingush
EFLAGS word and kernel address in the spin lock stack frame.

Signed-off-by: default avatarAndi Kleen <ak@suse.de>
parent 0cb91a22

arch/x86_64/kernel/time.c

+8 −13
Original line number Diff line number Diff line
@@ -189,20 +189,15 @@ unsigned long profile_pc(struct pt_regs *regs) 
{

	unsigned long pc = instruction_pointer(regs);



	/* Assume the lock function has either no stack frame or only a single 

	   word.  This checks if the address on the stack looks like a kernel 

	   text address.

	   There is a small window for false hits, but in that case the tick

	   is just accounted to the spinlock function.

	   Better would be to write these functions in assembler again

	   and check exactly. */

	/* Assume the lock function has either no stack frame or a copy

	   of eflags from PUSHF

	   Eflags always has bits 22 and up cleared unlike kernel addresses. */

	if (!user_mode(regs) && in_lock_functions(pc)) {

		char *v = *(char **)regs->rsp;

		if ((v >= _stext && v <= _etext) ||

			(v >= _sinittext && v <= _einittext) ||

			(v >= (char *)MODULES_VADDR  && v <= (char *)MODULES_END))

			return (unsigned long)v;

		return ((unsigned long *)regs->rsp)[1];

		unsigned long *sp = (unsigned long *)regs->rsp;

		if (sp[0] >> 22)

			return sp[0];

		if (sp[1] >> 22)

			return sp[1];

	}

	return pc;

}