And for your other question concerning the plugin:

1. it's been fixed only recently
2. it's not completely fixed with this regard!

See ThreadedFFIPlugin>>checkAlignmentOfStructSpec:OfLength:StartingAt:
We are always using the filedSize in case of atomic type as
fieldAlignment...
So it ain't gonna work for double/longlong/ulonglong on 32 bits linux
(unless library is compiled with -malign-double or other exotic flags, but
how could FFI guess that...)
Ideally, the alignment would be occupying some bits in the type spec.
Or we hardcode the well known exception in a second place.
Anyway, the plugin also had to duplicate the alignment algorithm as you can
see...

We live in a world full of such accidental complexity...
At least, while mankind is taking care of such detail, this leaves less
time for killing each other, so let's declare that it's a good thing ;)

Le ven. 29 mai 2020 à 17:37, Nicolas Cellier <
nicolas.cellier.aka.nice at gmail.com> a écrit :

> Found a 32bits debian VM:
>
> st at debi9:~$ gcc test_align.c
> st at debi9:~$ ./a.out
> size of x = 16
> size of y = 16
>
> So keep the code, just correct it!
>
> Le ven. 29 mai 2020 à 17:01, Nicolas Cellier <
> nicolas.cellier.aka.nice at gmail.com> a écrit :
>
>> Try with this:
>>
>> cat > test_align.c <<END
>> #include <stdio.h>
>>
>> struct foo1 {int a; long long b; int d;};
>> struct foo2 {int a; double c; int d;};
>>
>> int main() {
>> struct foo1 x;
>> struct foo2 y;
>> printf("size of x = %d\n",sizeof(x));
>> printf("size of y = %d\n",sizeof(y));
>> return 0;
>> }
>> END
>> i686-w64-mingw32-gcc test_align.c
>>  ./a.exe
>>
>> size of x = 24
>> size of y = 24
>>
>> so at leat in windows (mingw) the alignment is 8 bytes for both long long
>> and double.
>> I have no 32bits linux handy, but it should be easy enough to pass the
>> same test...
>>
>> Le ven. 29 mai 2020 à 16:45, Nicolas Cellier <
>> nicolas.cellier.aka.nice at gmail.com> a écrit :
>>
>>> Good catch!
>>> Wikipedia page does not even agree on longlong... But it's not the
>>> ultimate normative reference, better check by ourselves!
>>> https://en.wikipedia.org/wiki/Data_structure_alignment
>>>
>>> Le ven. 29 mai 2020 à 15:53, Marcel Taeumel <marcel.taeumel at hpi.de> a
>>> écrit :
>>>
>>>> Hi, there.
>>>>
>>>> In ExternalType class >> #initializeAtomicTypes, there is an
>>>> interesting claim and a piece of dead code:
>>>>
>>>> "On 32 bits Windows and MacOS, double and long have an alignment of 8.
>>>> But on Linux, their alignment is 4"
>>>> (Smalltalk wordSize = 4 and: [Smalltalk platformName = 'unix']) ifTrue:
>>>> [
>>>> (#('double longlong ulonglong') includes: typeName) ifTrue: [
>>>> byteAlignment := 4
>>>> ]
>>>> ].
>>>>
>>>> As you can see, there are single quotes missing and so will the path
>>>> "byteAlignment  := 4" never be reached.
>>>>
>>>> I tried to figure out whether one should either fix the conditional or
>>>> remove the entire passage. Maybe this got long fixed inside the FFI plugin?
>>>>
>>>> Best,
>>>> Marcel
>>>>
>>>>
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