[Vm-dev] Alien/FFI issue with large struct passed as value and how to load vmmaker?

[Ben Coman]

On Wed, 3 Apr 2019 at 22:54, Holger Freyther <holger at freyther.de> wrote:

>
> Hi,
>
> Sorry if this sounds ignorant but I am not sure how to do this with
> Opensmalltalk VM. How do I get a working VMMaker loaded into a Pharo image
> these days? It was quite simple in the pharo-vm days but now I am not even
> sure where to start looking?
>

You haven't said what you've tried.  This looks updated recently...
http://wiki.squeak.org/squeak/vmmaker

btw, I see an experimental git repo for VMMaker ...

https://github.com/feenkcom/opensmalltalk-vm/tree/pullrequest4/vmmaker/smalltalksrc/VMMaker

but this is not what the production VMs are built from.


I want to debug a FFI problem I see with Ben's clang-c bindings. I get a
> callback from C with three arguments and one of them is of type CXCursor
> (it needs to be passed on the stack):
>

You are referring this page then...?

https://blog.openinworld.com/2016/09/pharo-libclang-ffi-part-4-ast-walking-with-visitors-callbacks/

Which part of it are you up to?


struct CXCursor {
>         int
>         enum
>         void *ptr[3];
> };
>
> It's represented as FFIExternalStructure subclass: #CXCursor.


For more context for interested readers, CxCursor definition is shown
here...
https://blog.openinworld.com/2016/09/pharo-libclang-ffi-part-3-loading-an-ast/



In the case of the callback the handle is an instance of
> FFIExternalStructureReferenceHandle with an Alien embedded into it.
>

Wow, those posts were back in 2016. How time flies. Its vague, but I don't
remember ever seeing class FFIExternalStructureReferenceHandle or Alien
anywhere.
I'll have to freshly re-follow the posts myself to review.



> I am trying to understand if the bug is on handling the callback when the
> CXCursor is created or when trying to push it onto the stack when making a
> call.
>
> The memory on the stack is turned into an Alien. And
> Alien>>#referenceStructAt:length: doesn't return a ByteArray but the
> FFIExternalStructureReferenceHandle with the Alien in it.
>
> At the same time I think FFIPlugin>>#ffiPushStructureContentsOf: doesn't
> seem to deal with FFIExternalStructureReferencehandle (or handle being an
> Alien).
>

I'm not familiar with that part of it.  Hopefully someone else can chime in.
btw, did you do the whole series of post individually, or bulk load the
code from... http://smalltalkhub.com/#!/~BenComan/LibclangPractice

cheers -ben
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