From cddda71cfb4146a1b441f64e96c9b07f347911e5 Mon Sep 17 00:00:00 2001
From: Rodrigo Arias <rodrigo.arias@bsc.es>
Date: Fri, 19 Nov 2021 16:22:37 +0100
Subject: [PATCH] Early duplicate state detection in channels

These checks allows the emulator to abort at the moment in which two
consecutive states are going to be emitted by the channel, showing the
culpirit in the backtrace. Waiting for the check in chan_emit() hides
the source of the problem.
---
 chan.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 63 insertions(+), 1 deletion(-)

diff --git a/chan.c b/chan.c
index 3489ccf..db8dbb9 100644
--- a/chan.c
+++ b/chan.c
@@ -172,6 +172,25 @@ chan_set(struct ovni_chan *chan, int st)
 
 	assert(chan->enabled);
 
+	/* Only chan_set can set the 0 state */
+	if(st < 0)
+	{
+		err("chan_set: cannot set a negative state %d\n", st);
+		abort();
+	}
+
+	/* Don't enforce this check if we are dirty because the channel was
+	 * just enabled; it may collide with a new state 0 set via chan_set()
+	 * used by the tracking channels */
+	if(chan->dirty != CHAN_DIRTY_ACTIVE
+			&& chan->lastst >= 0
+			&& chan->lastst == st)
+	{
+		err("chan_set id=%d cannot emit the state %d twice\n",
+				chan->id, st);
+		abort();
+	}
+
 	if(chan->n == 0)
 		chan->n = 1;
 
@@ -205,9 +224,22 @@ chan_push(struct ovni_chan *chan, int st)
 
 	assert(chan->enabled);
 
+	if(st <= 0)
+	{
+		err("chan_push: cannot push a non-positive state %d\n", st);
+		abort();
+	}
+
 	/* Cannot be dirty */
 	assert(chan->dirty == 0);
 
+	if(chan->lastst >= 0 && chan->lastst == st)
+	{
+		err("chan_push id=%d cannot emit the state %d twice\n",
+				chan->id, st);
+		abort();
+	}
+
 	if(chan->n >= MAX_CHAN_STACK)
 	{
 		err("channel stack full\n");
@@ -248,6 +280,24 @@ chan_pop(struct ovni_chan *chan, int expected_st)
 	}
 
 	chan->n--;
+
+	/* Take the current stack value */
+	st = chan_get_st(chan);
+
+	/* A st == 0 can be obtained when returning to the initial state */
+	if(st < 0)
+	{
+		err("chan_pop: obtained negative state %d from the stack\n", st);
+		abort();
+	}
+
+	if(chan->lastst >= 0 && chan->lastst == st)
+	{
+		err("chan_pop id=%d cannot emit the state %d twice\n",
+				chan->id, st);
+		abort();
+	}
+
 	chan->t = *chan->clock;
 
 	mark_dirty(chan, CHAN_DIRTY_VALUE);
@@ -264,7 +314,19 @@ chan_ev(struct ovni_chan *chan, int ev)
 
 	/* Cannot be dirty */
 	assert(chan->dirty == 0);
-	assert(ev >= 0);
+
+	if(ev <= 0)
+	{
+		err("chan_ev: cannot emit non-positive state %d\n", ev);
+		abort();
+	}
+
+	if(chan->lastst >= 0 && chan->lastst == ev)
+	{
+		err("chan_ev id=%d cannot emit the state %d twice\n",
+				chan->id, ev);
+		abort();
+	}
 
 	chan->ev = ev;
 	chan->t = *chan->clock;