[Vm-dev] nested structures with FFI?

[Esteban Lorenzano]

> On 20 Aug 2015, at 21:48, Max Leske <maxleske at gmail.com> wrote:
> 
> 
>> On 20 Aug 2015, at 21:28, vm-dev-request at lists.squeakfoundation.org <mailto:vm-dev-request at lists.squeakfoundation.org> wrote:
>> 
>> Message: 1
>> Date: Thu, 20 Aug 2015 17:51:43 +0200
>> From: Esteban Lorenzano <estebanlm at gmail.com <mailto:estebanlm at gmail.com>>
>> Subject: [Vm-dev] nested structures with FFI?
>> To: Squeak Virtual Machine Development Discussion
>> 	<vm-dev at lists.squeakfoundation.org <mailto:vm-dev at lists.squeakfoundation.org>>
>> Message-ID: <4F31ED4B-6246-43D6-B85B-7215D8570D28 at gmail.com <mailto:4F31ED4B-6246-43D6-B85B-7215D8570D28 at gmail.com>>
>> Content-Type: text/plain; charset=utf-8
>> 
>> Hi,
>> 
>> I’m doing some tests with nested structures (to handle the conversion of NativeBoost-FFI to regular FFI) and I’m having some problems when accessing fields in the nested structure. 
>> For example, this tests: 
>> 
>> FFITestNestingStructure class>>#fieldsDesc 
>> 	^ #(
>> 		byte one;
>> 		FFITestStructure nested;
>> 		)
>> 
>> FFITestStructure class>>#fieldsDesc
>> 	^ #(
>> 		byte byte;
>> 		short short;
>> 		long long;
>> 		float float;
>> 		double double;
>> 		int64 int64;
>> 		)
>> 
>> (definition is NB-compatible, so do not take the differences with regular FFI into account)
>> 
>> testNestedStructure
>> 	| s1 |
>> 	
>> 	s1 := FFITestNestingStructure new.
>> 	s1 nested byte: 42.	
>> 	self assert: s1 nested byte = 42
>> 
>> testExternallyAllocatedNestedStructure
>> 	| s1 |
>> 	
>> 	s1 := FFITestNestingStructure externalNew.
>> 	self assert: s1 getHandle class = ExternalAddress.
>> 	s1 nested byte: 42.	
>> 	self assert: s1 nested byte = 42
>> 
>> 
>> fails always because 
>> 
>> s1 nested byte = 0. 
>> 
>> (which is obviously bad). 
>> 
>> I remember Eliot saying that structures with FFI was not being optimal, and I wonder (before start digging more in deep) if this could have something to do?
> 
> I use nested structs in NB for the libgit2 bindings and they work as advertised. There can be problems if some structure is packed (i.e. uses non-4-byte alignment for some field) but that shouldn’t apply in your test case.
> 
> Not sure if this helps you in any way but I thought I’d let you know :)

I do not think so :)
I’m quite sure this is not going to be a problem when using the ThreadedFFI backend instead ASMJIT… now my problem is with this backend, for the moment :) 

Esteban

> 
> Cheers,
> Max
> 
>> 
>> cheers, 
>> Esteban
> 

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