[Vm-dev] FFIExternalStructureReferenceHandle and pushing it to the stack

[Holger Freyther]

> On 4. Apr 2019, at 08:36, Holger Freyther <holger at freyther.de> wrote:


And I have a stand-a-lone testcase for Pharo as well:

https://github.com/zecke/pharo/commit/390f81241a7dfee546784453fa426bc1c218b39e


Any hint of how I can test (simulate?) and generate changes to ThreadedX64SysVFFIPlugin from Pharo (or how you normally do it in Squeak).

cheers
	holger


> In addition to my mail from yesterday to vm-dev I want to share the following example to illustrate the problem.  I have taken StructA and StructNested from the FFIExternalStructureReferenceHandle class comment and put it into Unclassified.st that is attached to this mail. I am also making a call to LibC's getpid and try to push StructNested to the stack. The ffiCall is failing before getpid is called (Bad argument to external function).
> 
> The reproducer is:
> 
> 	StructA new theNest anyCall.
> 
> 
> StructA has a ByteArray handle of the full struct. theNest returns an instance of StructNested with a FFIExternalStructureReferenceHandle. This makes sense as well. It can't be a copy of the ByteArray (or else updates would be invisible to the outer struct) and it can't be an ExternalAddress as StructA's handle might move in the Smalltalk heap.
> 
> I am not entirely sure how this is should work but what do you think of:
> 
> 1st) Extending ExternalStructure class comment to list FFIExternalStructureReferenceHandle as possible handle type? I think we would only describe the reality.
> 
> 
> 2nd) ThreadedFFIPlugin>>#ffiPushStructureContentsOf: should be aware of FFIExternalStructureReferenceHandle and know how to reach the handle. Or should there be something in the image converting this to a ByteArray when being pushed as value in a ffiCall?
> 
> 
> comments/ideas?
> 
> 
> <Unclassified.st>