diff --git a/sys/amd64/include/cpufunc.h b/sys/amd64/include/cpufunc.h
--- a/sys/amd64/include/cpufunc.h
+++ b/sys/amd64/include/cpufunc.h
@@ -364,6 +364,15 @@
 	return (low | ((uint64_t)high << 32));
 }
 
+static __inline uint64_t
+rdtscp_aux(uint32_t *aux)
+{
+	uint32_t low, high;
+
+	__asm __volatile("rdtscp" : "=a" (low), "=d" (high), "=c" (*aux));
+	return (low | ((uint64_t)high << 32));
+}
+
 static __inline uint32_t
 rdtsc32(void)
 {
diff --git a/sys/i386/include/cpufunc.h b/sys/i386/include/cpufunc.h
--- a/sys/i386/include/cpufunc.h
+++ b/sys/i386/include/cpufunc.h
@@ -403,6 +403,15 @@
 	return (rv);
 }
 
+static __inline uint64_t
+rdtscp_aux(uint32_t *aux)
+{
+	uint64_t rv;
+
+	__asm __volatile("rdtscp" : "=A" (rv), "=c" (*aux));
+	return (rv);
+}
+
 static __inline uint32_t
 rdtsc32(void)
 {