Do you mean within callback()? I put those lines before and after the call to the actual perl sub, but both cases still result in segfault.

This is example I'm looking at https://metacpan.org/pod/perlembed#Fiddling-with-the-Perl-stack-from-your-C-program and I think you could copy this example and turn it into void callback(),

something like

Read more... (1365 Bytes)

Yes , I understand perlcall gives simpler example like you have , but its what I would try, to see if anything sticks :D

I greatly appreciate the feedback to try, AnonyMonk!

With the last code, static didn't work, so I removed that. I also initialized a and b. This very slightly modified declaration (yep, I corrected the def as well):

void callback(){
    int a = 10;
    int b = 20;
    dSP;
    ENTER;
    SAVETMPS;
    PUSHMARK(SP);
    XPUSHs(sv_2mortal(newSViv(a)));
    XPUSHs(sv_2mortal(newSViv(b)));
    PUTBACK;

    call_pv("p_callback", G_DISCARD|G_NOARGS);

    SPAGAIN;

    printf("%d to the %dth power is %d.\n", a, b, POPi);

    PUTBACK;
    FREETMPS;
    LEAVE;
}
[download]

...with the exact same otherwise all around, produces:

in init
in perl callback
Use of uninitialized value in subroutine entry at c_extern_call_perl.p
+l line 11.
10 to the 20th power is -474476032.
Segmentation fault
[download]

So, callback() is working perfectly on the direct call from the perl code, it still registers ok in the external function, but as soon as the callback is triggered from extern, it breaks, from my estimation, at or before the call to call_pv().

Update: I moved around some comments, and it segfaults on anything following the call to dSP().

Perhaps I'm XY Problem-ing this. Here's what I want...

• extern C function requires a void func(void) function pointer as a callback
• I would really prefer not to modify the external code, if I can avoid it (I'd really like it to be void func(const char *string) realistically, I think, but I am a C newb)
• to avoid the void/void, on the perl side, I want a user to send in a cref to a Perl method, which calls an XSUB to send in a pre-defined XSUB callback that points to the cref to the external C function (this all works)
• when an event is triggered, and the already-registered callback in the extern is called, it should call the user-supplied cref in the main module's (in the case I've exampled here, the main script) perl code

Am I making sense here? Perhaps I'm thinking this totally wrong. I'm going to keep pounding on this because I know there's got to be a way :) I'm just not experienced enough in all of the cross-language comms, and using XS. I'm having fun though