[Vm-dev] bug when instantiating ExternalData (to return void* from FFI)

[Esteban Lorenzano]

Hi Eliot, list

I found a bug :)
With latest VM (32 bits, using PharoVM flavour), I crash the VM when executing this: 

LGitError giterr_last.

LGitError class>>giterr_last
	^ self call: #(void *giterr_last()) options: #(  )

this is a very basic FFI call, and should answer an ExternalData instance (pointing to NULL, in this case). 

Digging into it, I found at a point (when instantiating the pointer) it answers nil instead an instantiated ExternalData, and this is because in 

Spur32BitMemoryManager>>instantiateClass:indexableSize:

otherwise clause is: 

		otherwise: "non-indexable"
			[self cppIf: (PharoVM or: [true]) "Leave the old code but ignore it completely unless someone complains."
				ifTrue:
					[^nil]
				ifFalse:
					["some Squeak images include funky fixed subclasses of abstract variable
					  superclasses. e.g. DirectoryEntry as a subclass of ArrayedCollection.
					  Allow fixed classes to be instantiated here iff nElements = 0."
					 (nElements ~= 0 or: [instSpec > self lastPointerFormat]) ifTrue:
						[^nil].
					 numSlots := self fixedFieldsOfClassFormat: classFormat.
					 fillValue := nilObj]].

So it will always answer nil/NULL.
Now, I don’t know why it was commented out, but since there it says  "Leave the old code but ignore it completely unless someone complains.”, I complain :D

Thing is… if I restore old code it works fine.

Question is: should we restore that code? or this shows a deeper problem?

cheers, 
Esteban