On Sun, May 31, 2020 at 12:21 PM Marcel Taeumel marcel.taeumel@hpi.de wrote:
Hi Eliot,
those values are constant on a platform, right? So, we could make an external-shared-pool for it... :-)
Right. I think that the primitive is a simple way of generating the data. At least it is organized with the rest of he plugin. Having a separate program for it is perhaps a maintenance problem. So I think the primitive makes sense.
I am almost done with the next iteration on FFI-Pools package. I am just cleaning up, adding some class comments, ...
Cool!!
Best, Marcel
Am 31.05.2020 01:58:46 schrieb Eliot Miranda eliot.miranda@gmail.com: Hi Nicolas, Hi Marcel,
On May 29, 2020, at 8:02 AM, Nicolas Cellier < nicolas.cellier.aka.nice@gmail.com> wrote:
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;};
Here’s a suggestion. We add a primitive To the ThreadedFFIPlugin that answers structure alignment thusly:
- the primitive takes as it’s argument the numeric code for the integer or
float type or a structure as used in the compiled type specs
- the primitive answers the alignment of the data type in a struct that
looks like this:
struct alignment_of_longlong { char pad_to_force_alignment; long long element; }
return &((struct alignment_of_longlong *)0)-> element);
struct alignment_of_double { char pad_to_force_alignment; long long element; }
return &((struct alignment_of_double *)0)-> element);
struct alignment_of_struct { char pad_to_force_alignment; struct { char element; } element; }
return &((struct alignment_of_struct *)0)-> element);
etc
Then we can remember these alignments in class vars of, say, ExternalStructure, check them on start-up, and resize/update ExternalStructure if any of the values change.
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@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@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