Include prims.o in libcamlrun_shared.so

[yallop]

I'd like to use libcamlrun_shared.so from other languages, but it has an undefined symbol caml_names_of_builtin_cprim:

$ python3 -c "import ctypes; ctypes.CDLL('runtime/libcamlrun_shared.so')"

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python3.11/ctypes/__init__.py", line 376, in __init__
    self._handle = _dlopen(self._name, mode)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^
OSError: runtime/libcamlrun_shared.so: undefined symbol: caml_names_of_builtin_cprim

This PR includes prims.o in the shared object so that the symbol is no longer undefined:

$ python3 -c "import ctypes; ctypes.CDLL('runtime/libcamlrun_shared.so')"
$

[yallop]

Is someone (perhaps @dra27 or @shindere) able to take a quick look at this? It shouldn't take long: it's just a one-line change to a Makefile, with a one-line test case in the description that shows how it fixes a bug.

[shindere]

Yes will look into it, sorry for the delay.

[shindere]

@yallop I am wondering why you have chosen to add runtime/prims.$(O) as
an explicit prerequisite of runtime/libcamlrun_shared.$(SO), rather
than adding the file to the (beginning of the) definition of
libcamlrunpic_OBJECTS variable?

To rephrase, are you sure this file needs to be added only to this target
and not to all the other targets built from libcamlrunpic_OBJECTS?

[dra27]

Sorry for the slowness here, but I think this may need an additional .so - the purpose of that library is as alternative to -lcamlrun where those symbols are defined elsewhere (e.g. by -output-obj and friends - cf. the way ocamlrun.exe itself is assembled) ... the _shared is a trick which allows it to be used with -runtime-variant (IIRC - I haven't dug into the various notes I have about this part)

I wonder if the better fix is to introduce libcamlrun.so with prims.o included and leave libcamlrun_shared.so as-is?

[shindere]

Thanks a lot for your insight here David! For sure the suggedted approach has the benefit of not breaking / touching anything existing!

[yallop]

Thank you for the analysis, @shindere and @dra27!

While it would be useful to me to have a shared library that I could use directly, it's not clear that the effort of building a new libcamlrun.so is worth it (since it's easy enough to relink prims.o together with libcamlrun_shared.so for my purposes).

[dra27]

Are additional libraries (e.g. Unix) also dynamically loaded? The linking "model" (it's a slightly grand word for it!) with those .a and .so basically ignores dynamic loading of C, so if what you're doing would otherwise never involve having to relink .so files, I can certainly see a gap in the distribution for providing an actual "here is the basic OCaml runtime as a self-contained DLL"

[yallop]

Are additional libraries (e.g. Unix) also dynamically loaded?

I don't have a need for that at the moment; I only need to load the compiler code itself.