trampoline.c

#include <stdint.h>
#include <stdio.h>
#include <trampoline.h>

static void *i;

static int fn(void)
{
    printf("%i\n", (int)(uintptr_t)i);
    return 0;
}

int main(void)
{
    int (*f)(void) = alloc_trampoline(fn, &i, (void *)42UL);                                                                                                                                                                                                                   

    f();

    return 0;
}

$ gcc trampoline.c -ltrampoline
$ ./a.out
42