From 0a3c5f5ac686d02b29a0b8bef1d89a76a01808e0 Mon Sep 17 00:00:00 2001
From: Slava Pestov <slava@factorcode.org>
Date: Mon, 14 Dec 2009 01:09:04 -0600
Subject: [PATCH] vm: fep out if monotonic counter decreases

---
 vm/run.cpp | 5 ++++-
 vm/vm.cpp  | 3 ++-
 vm/vm.hpp  | 4 ++++
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/vm/run.cpp b/vm/run.cpp
index 1bb2e0c44e..583d4f658b 100755
--- a/vm/run.cpp
+++ b/vm/run.cpp
@@ -15,7 +15,10 @@ void factor_vm::primitive_system_micros()
 
 void factor_vm::primitive_nano_count()
 {
-	box_unsigned_8(nano_count());
+	u64 nanos = nano_count();
+	if(nanos < last_nano_count) critical_error("Monotonic counter decreased",0);
+	last_nano_count = nanos;
+	box_unsigned_8(nanos);
 }
 
 void factor_vm::primitive_sleep()
diff --git a/vm/vm.cpp b/vm/vm.cpp
index 72c63292fd..d911b80227 100755
--- a/vm/vm.cpp
+++ b/vm/vm.cpp
@@ -10,7 +10,8 @@ factor_vm::factor_vm() :
 	current_gc(NULL),
 	gc_events(NULL),
 	fep_disabled(false),
-	full_output(false)
+	full_output(false),
+	last_nano_count(0)
 {
 	primitive_reset_dispatch_stats();
 }
diff --git a/vm/vm.hpp b/vm/vm.hpp
index 2d78bae709..a3019bd054 100755
--- a/vm/vm.hpp
+++ b/vm/vm.hpp
@@ -87,6 +87,10 @@ struct factor_vm
 	/* Incrementing object counter for identity hashing */
 	cell object_counter;
 
+	/* Sanity check to ensure that monotonic counter doesn't
+	decrease */
+	u64 last_nano_count;
+
 	// contexts
 	void reset_datastack();
 	void reset_retainstack();