[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: Andi Kleen <ak@suse.de>
diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c
index 560ed94..ea00915 100644
--- a/arch/x86_64/kernel/time.c
+++ b/arch/x86_64/kernel/time.c
@@ -189,20 +189,15 @@
{
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;
}
