On 20 Aug 2015, at 21:48, Max Leske <maxleske@gmail.com> wrote:

On 20 Aug 2015, at 21:28, vm-dev-request@lists.squeakfoundation.org wrote:

Message: 1
Date: Thu, 20 Aug 2015 17:51:43 +0200
From: Esteban Lorenzano <estebanlm@gmail.com>
Subject: [Vm-dev] nested structures with FFI?
To: Squeak Virtual Machine Development Discussion
<vm-dev@lists.squeakfoundation.org>
Message-ID: <4F31ED4B-6246-43D6-B85B-7215D8570D28@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