lazurite $ cat fortytwo.s

        .global _fortytwo
_fortytwo:
        movl    $42, %eax
        ret

lazurite $ cat main.c
#include <stdio.h>

extern int fortytwo (void);

int main (void) {
  printf ("fortytwo = %d\n", fortytwo());
  return 0;
}

lazurite $ cc fortytwo.s main.c

lazurite $ ./a.out
fortytwo = 42

lazurite $ _