update: You can see code snips I ended up with that works are in Re: XS: Passing an external library's function a Perl XS callback.

Disclaimer: cross-posted at StackOverflow.

I hope I'm describing and depicting my issue properly... In XS, I'm trying to send a callback into an external library's function, where the callback has Perl specific functions. The XSUB is passed as a function pointer to an external C function. The XSUB callback being sent in turn calls back to a sub in the main perl application:

void callback(){
    dSP;
    PUSHMARK(SP);
    call_pv("p_callback", G_DISCARD|G_NOARGS);
}

// example extern call

externFunc(&callback);
[download]

This segfaults. I think it's because the external library doesn't understand the perl functions that are being called. Things work fine if I call the C callback() function directly though.

Is there some magic that I can do to make the external library "see" the Perl C functions, or am I doing something wrong?

Here's the code I'm testing with:

use warnings;
use strict;

use Inline ('C' => 'DATA', libs => '-lwiringPi');

init();

# the below call is a local XS function that
# sets up the external function with the callback

setInterrupt(27, 3);

# direct call

callback();

# on() triggers the external function to exec
# the callback

on(27);

sub p_callback {
    print "in perl callback\n";
}

__DATA__
__C__

#include <stdlib.h>
#include <stdio.h>
#include <wiringPi.h>

void init();
void on(int pin);
void off(int pin);
void setInterrupt(int pin, int edge);
void callback();

void init(){
    printf("in init\n");
    wiringPiSetup();
}
void on(int pin){
    pinMode(pin, 1);
    digitalWrite(pin, 1);
}

void off(int pin){
    digitalWrite(pin, 0);
    pinMode(pin, 0);
}

void setInterrupt(int pin, int edge){
    wiringPiISR(pin, edge, &callback);
}

void callback(){
    dSP;
    PUSHMARK(SP);
    call_pv("p_callback", G_DISCARD|G_NOARGS);
}
[download]

Output:

in init
in perl callback
Segmentation fault
[download]

If I remove the perl specific C calls from within the callback and just do a printf() or other pure-C work, things proceed without a segfault.

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