[squeak-dev] 64 bit FFI (was: porting Croquet to Squeak6.0 alpha...)

Nicolas Cellier nicolas.cellier.aka.nice at gmail.com
Thu Mar 12 12:21:03 UTC 2020

Hi all,
beware of FFI 'long' and 'ulong'.
They are currently meaning (32 bits) int and unsigned int!
This dates back from the 80s when there were still odd OS with segmented
memory and 16-bits int.
long was thought as a safe int32_t at that time... and still means just
that in current FFI.

I'd like to replace them with 'int' and 'uint', but we need to ensure
backward compatibility etc...

FFI has ExternalType signedLongLong or just 'longlong' and ExternalType
unsignedLongLong or 'ulonglong' which are 64 bits on all architectures.
See implementors of #initializeAtomicTypes #initializeFFIConstants

If you want a type that can hold a pointer on both 32 and 64bits arch, then
it's doable with a FFI type alias
For example I have things like this in HDF5 module
Notice the single #(fieldName fieldType) which defines an alias, while
ordinary FFI struct gets an array of #(fieldName fieldType)
(and replace Size_t with Intptr_t if the purpose is hodling a pointer,
otherwise the ayatollahs of C standard will lash you)

ExternalStructure subclass: #'Size_t'
    instanceVariableNames: ''
    classVariableNames: ''
    poolDictionaries: ''
    category: 'HDF5-External-atomic'

Size_t class >>fields
    "Size_t defineFields"
    ^Smalltalk wordSize = 4
        ifTrue: [#( value 'ulong')]
        ifFalse: [#( value 'ulonglong')]

However the "fields" must be re-generated when platform changes...
I tried to automate that sometimes ago, see:

ExternalStructure class>>install
     "Resuming the image on another architecture may require a
re-compilation of structure layout."
     | newPlatform |
     newPlatform := Smalltalk platformName.
     PreviousPlatform = newPlatform
             [self recompileStructures.
            PreviousPlatform := newPlatform]

It works if you switch from Win64 to MacOS64 for example...
However, this mechanism is not used yet at time of code loading, so
importing code generated on a different platform won't automatically update
the structures (or alias) - the FFI package has no mechanism for that
(maybe we could add a hook in MC?).

Le mer. 11 mars 2020 à 23:58, Bert Freudenberg <bert at freudenbergs.de> a
écrit :

> I'd suggest to get OpenGL working outside of Croquet first:
> http://www.squeaksource.com/CroquetGL.html
> Step 1: Verify this works in 32 bits. (assuming you are doing this on
> Linux, you can run 32 bit Squeak side-by-side with the 64 bit one)
> Step 2: Make it work in 64 bits.
> The second step requires that you understand how FFI works, and how it
> handles e.g. pointers and integer sizes.
> I am assuming we do have a working 64 bit FFI, at least for x86_64
> machines.
> E.g. the OGLUnix>>glExtGetProcAddress: method returns a pointer. On a 32
> bit system, that fits into a 'ulong' which is 32 bits. On a 64 bit system,
> a pointer is 64 bits wide so it would not fit into a 32 bit word. Now I
> don't know how many bits 'ulong' has in our 64 bit FFI, but that
> declaration may have to change. Etc. pp.
> If you have questions about FFI then those are best directed at the vm-dev
> list since it is dealing with VM-level interfaces. CC'ing, please follow up
> there.
> - Bert -
> On Wed, Mar 11, 2020 at 2:54 PM gettimothy via Squeak-dev <
> squeak-dev at lists.squeakfoundation.org> wrote:
>> Okey dokey,
>> Poking along, there is a stray glyph in OGLUnix openGLLibraryName after
>> openGLLibraryName
>> ^Smalltalk osVersion = 'linux'
>> ifTrue: ['libGL.so.1']
>> ifFalse: ['GL']
>> I removed it in my install and got past that error.
>> Working exclusively with Croquet(Master)...
>> My next error is in OGLUnixX11LE(OpenGL)>>glMatrixMode:
>> glMatrixMode: mode
>> "This method was automatically generated."
>> "void glMatrixMode(GLenum mode);"
>> <apicall: void 'glMatrixMode' (ulong) module: '#openGLLibraryName'>
>> ^self externalCallFailed
>> The <apicall:...> fails
>> How to think about this?
>> Is Croquet behind OpenGL latest?
>> Would teaching myself OpenGL programming be of use to the Croquet project?
>> cheers,
>> tty
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