VM crashes on spectest

[tolauwae]

Spectest now fails because latch loses connection with the VM. I suspect the VM crashes for the first suite unwind.wast because of a segmentation fault in Debugger::dumpLocals, leading to the failed connection and timeout.

WARDuino/src/Debug/debugger.cpp

Lines 581 to 582 in 050bdc5

	int firstFunFramePtr = m->csp;
	while (m->callstack[firstFunFramePtr].block->block_type != 0) {

Here m->csp = -1 leading to a segmentation fault when it is used as an array index on line 582.

Originally posted by @tolauwae in #339 (comment)

[tolauwae]

This should be a general problem with spectest, but somehow is not (deeper look at latch might clarify why). In essence, the debugger assumes that the VM will load a module and setup a main call, which pushes a block thereby increasing the callstack pointer (m->csp).

However, for the spectests we load a module and do not run any function. This is why we added this if statement to WARDuino::run_module:

WARDuino/src/WARDuino/WARDuino.cpp

Lines 940 to 948 in 82a8afd

	// execute main
	if (fidx != UNDEF) {
	this->invoke(m, fidx);
	return m->stack->value.uint32;
	}
	// wait
	m->warduino->debugger->pauseRuntime(m);
	return interpreter->interpret(m, true);

For spectests the fidx = UNDEF. So no invoke gets called, no block pushed. When the interpret function gets called in the waiting mode, we still have m->csp = -1. So if you send a dump command to the debugger you get the segmentation fault above.

It is a mystery to me at the moment why we didn't encounter this problem earlier.