Implementing setjmp and longjmp in C without built in functions or assembly (getting incorrect return values)

I'm trying to test 2 of my functions that sort of mimic setjmp and longjmp for a homework - which is pretty difficult since we're not allowed to use built in functions or assembly asm() to implement the longjmp and setjmp functions. (Yes, that's really the assignment.)

Problem: I keep getting wrong return values. So, in short, when main() calls foo() and foo() calls bar(), and bar() calls longjump(), then bar() should not return to foo() but instead setjmp() should return to main with return value of 1 which should print "error" (see main() below).

Instead, my output comes out as:

start foo
start bar
segmentation fault

The segmentation fault, i tried fixing by initializing the pointer *p with malloc, but that didn't seem to do anything. Although, would the segmentation fault, be the reason why im not getting the correct return values?

code:

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

int setjmp(int v);
int longjmp(int v);
int foo(void);
int bar(void);
int *add;


int main(void) {

    int r;

    r = setjmp(r);
    if(r == 0) {
        foo();
        return(0);
    } else {
        printf("error\n");
        return(2);
    }

}

int _main(void) {
    return(0);
}

int setjmp(int v)
{
    add = &v;
    return(0);
}

int longjmp(int v)
{
    int *p;
    p = &v;
    *(p - 1) = *add;
    return(1);
}

int foo(void) {
    printf("start foo\n");
    bar();
    return(0);
}

int bar(void) {
    int d;
    printf("start bar\n");
    longjmp(d);
    return(0);
}