typedef void (*fp_t)(void);

fp_t func(fp_t param)
{
    return (void *)0;          /* line A */
}

int main(void)
{
    fp_t t = (void *)0;       /* line B */
    t = (void *)0;            /* line C */
    return func((void *)0)    /* line D */
               == (void *)0;
}

5: warning: conversion from `pointer to void' to `pointer to void function(void)' is compiler dependent
10: warning: conversion from `pointer to void' to `pointer to void function(void)' is compiler dependent
11: warning: conversion from `pointer to void' to `pointer to void function(void)' is compiler dependent
12: warning: conversion from `pointer to void' to `pointer to void function(void)' is compiler dependent