[Vm-dev] SmartSyntaxInterpreterPlugin code generation issue

[Levente Uzonyi]

Hi All,

I found a bug in SocketPlugin which will crash the VM when triggered. 
While tracking the bug down, I found that SocketPlugin is a subclass of 
SmartSyntaxInterpreterPlugin and the cause of the bug is flawed code 
generation.

This line of smalltalk code (from SocketPlugin >> #primitiveSocket:connectTo:port:)

 	self primitive: 'primitiveSocketConnectToPort' parameters: #(#Oop #ByteArray #SmallInteger ).

is translated to[1]

 	socket = stackValue(2);
 	success(isBytes(stackValue(1)));
 	address = ((char *) (firstIndexableField(stackValue(1))));
 	port = stackIntegerValue(0);
 	if (failed()) {
 		return null;
 	}

The problem here is that the code checks if stackValue(1) is a bytes 
object, but the result of the check is only used after all arguments are 
read and converted.
So even if the second argument is not a bytes, the third line of the 
snipper above will treat is as a bytes object and firstIndexableField will 
cause segmentation fault.

I presume that other SmartSyntaxInterpreterPlugins have the same argument
validation issues, so it would be best if the code generator were fixed.


Levente

[1] https://github.com/OpenSmalltalk/opensmalltalk-vm/blob/Cog/src/plugins/SocketPlugin/SocketPlugin.c#L1137