[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>

1 files changed, 8 insertions, 13 deletions

diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c
index 560ed944dc0e..ea00915d393a 100644
--- a/arch/x86_64/kernel/time.c
+++ b/arch/x86_64/kernel/time.c
@@ -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;
 }