Generated code differences accross OS

[Maurizio Cimadamore]

AFAIK, the only difference is that, depending on the glut library in 
use, the parameter name is different, and the resulting function pointer 
factory is also different (because we use the parameter name to infer a 
good factory name).

I think that, as you point out, this naming strategy is a little 
unstable, as small differences (e.g. parameter names) end up with 
incompatible bindings.

We do not have a page listing these kind of issues (we need to improve 
jextract documentation, we are aware of that). On top of my mind, 
differences can include:

* type mismatches (e.g. `long` means 32 bits on windows, and 64 bits on 
linux)
* padding in structs might vary (largely because of the above)
* in some platforms some additional functions/struct members might be 
defined
* macros vs. function differences - e.g. a function might be a real 
shared library function on one platform/OS and just a macro in another

Assuming the library is written in a portable way (e.g. mainly avoids to 
refer to types such as `long`), things should work relatively well - but 
of course this is C and it is hard to generalize too much. In other 
words, your mileage when reusing same extracted sources across 
platforms/os is gonna vary, regardless of how smart jextract naming 
choices are.

That said, if clients generate new bindings for each platforms, I think 
jextract should try and depend only on public API names - otherwise it 
becomes harder for clients of bindings (since a member can have name X 
in one platform/OS and name Y in another).

So, assuming we fix this, what would be a good naming strategy for 
callback factories? If we don't want to depend on the parameter name, an 
alternative could be:

<funcName>$upcall

or, if the same function has more than one:

<funcName>$upcall$<pos>

where `pos` is the callback parameter index in the function signature.

Would that be satisfactory?

Maurizio



On 23/11/2021 11:17, Martin Pernollet wrote:
> Hi,
>
> There is difference in code generated on Ubuntu and MacOS, e.g. :
>
> glutReshapeFunc$func on MacOS
> glutReshapeFunc$callback on Ubuntu
>
> Will this remain as is in future versions of JExtract? If this is intentional, what is the reason for this?
>
> This is a bit annoying for generating multiplatform bindings because this will requires writing (or generating) a wrapper on the generated code.
>
> I am interested if someone knows a page discussing all differences that may arise in code generated on different OS.
>
> Thanks,
>
> Martin