From 4f8a9229c72b1a5e1ee6d4bf463ac022280d15f3 Mon Sep 17 00:00:00 2001
From: John Bates <jbates@chromium.org>
Date: Fri, 10 Dec 2021 11:42:46 -0800
Subject: [PATCH] add aarch64 cntvct counter support

---
 src/percetto.cc | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/src/percetto.cc b/src/percetto.cc
index d2b12a8..ed092f3 100644
--- a/src/percetto.cc
+++ b/src/percetto.cc
@@ -23,9 +23,8 @@
     defined(_M_AMD64)
   #define HAS_RDTSC
 #endif
-#if defined(_M_ARM) || defined(_M_ARMT) || defined(__arm__) || \
-    defined(__thumb__) || defined(__aarch64__)
-  // TODO(jbates): support ARM CPU counter
+#if defined(__aarch64__)
+  #define HAS_CNTVCT
 #endif
 
 #include "percetto.h"
@@ -225,11 +224,15 @@ static BuiltinClock GetBuiltinClockIdFrom(clockid_t clockid) {
 }
 
 static inline uint64_t GetCpuTicks() {
-  #ifdef HAS_RDTSC
+#ifdef HAS_RDTSC
   return __rdtsc();
-  #else
+#elif defined(HAS_CNTVCT)
+  uint64_t vct;
+  asm volatile("mrs %0, cntvct_el0" : "=r"(vct));
+  return vct;
+#else
   return 0;
-  #endif
+#endif
 }
 
 static inline uint64_t GetTimestampNs() {