From 6b7caa6c473674043d275f532b2f0253819bd612 Mon Sep 17 00:00:00 2001
From: "Peter H. Froehlich" <peter.hans.froehlich@gmail.com>
Date: Wed, 21 Oct 2015 18:43:02 -0400
Subject: [PATCH] The rdtsc(p) instruction.

---
 x86.h | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/x86.h b/x86.h
index 3949900..c171527 100644
--- a/x86.h
+++ b/x86.h
@@ -1,4 +1,5 @@
 // Routines to let C code use special x86 instructions.
+// Syntax reminder: (instructions : output : input : clobber)
 
 static inline uchar
 inb(ushort port)
@@ -121,7 +122,7 @@ static inline uint
 xchg(volatile uint *addr, uint newval)
 {
   uint result;
-  
+
   // The + in "+m" denotes a read-modify-write operand.
   asm volatile("lock; xchgl %0, %1" :
                "+m" (*addr), "=a" (result) :
@@ -139,11 +140,17 @@ rcr2(void)
 }
 
 static inline void
-lcr3(uint val) 
+lcr3(uint val)
 {
   asm volatile("movl %0,%%cr3" : : "r" (val));
 }
 
+static inline void
+rdtsc(uint *hi, uint *lo)
+{
+  asm volatile("rdtscp" : "=d" (*hi), "=a" (*lo) : : "%ecx");
+}
+
 //PAGEBREAK: 36
 // Layout of the trap frame built on the stack by the
 // hardware and by trapasm.S, and passed to trap().
-- 
2.50.1