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

#define obstack_chunk_alloc malloc
#define obstack_chunk_free free

//struct obstack *string_obstack;

int main(){
    struct obstack *string_obstack = (struct obstack *) malloc (sizeof (struct obstack));

    obstack_init (string_obstack);

    printf("address of obstack = %p, chunk_size = %d \n", string_obstack, string_obstack->chunk_size);
    printf("chunk = %p, object_base = %p next_free = %p \n\n", string_obstack->chunk, string_obstack->object_base, string_obstack->next_free);

    // Step 1: allocate the first chunk
    char *s = (char *) obstack_alloc (string_obstack, 4064);
    printf("======First chunk======\n");
    printf("before free: ((void *) lp = %p , (void *) (lp)->limit = %p \n", string_obstack->chunk, (void *) (string_obstack)->chunk->limit);
    printf("before free : prv = %p\n\n", string_obstack->chunk->prev);

    // Step 2: allocate the second chunk
    char *ss = (char *) obstack_alloc (string_obstack, 4064);

    printf("before free : address of s = %p\n", s);
    printf("before free : address of ss = %p\n\n", ss);

    printf("======Second chunk======\n");
    printf("before free: ((void *) lp = %p , (void *) (lp)->limit = %p \n", string_obstack->chunk, (void *) (string_obstack)->chunk->limit);
    printf("before free : prv = %p\n\n", string_obstack->chunk->prev);


    // Step 3: free the second chunk through obj
    printf("======Start to free======\n");
    char *t = s+4177;
    printf("before free : obj (string_obstack->chunk) = %p \n", string_obstack->chunk);
    printf("before free : obj (t) = %p \n\n", t);
    obstack_free (string_obstack, string_obstack->chunk); //problematic
    obstack_free (string_obstack, t);

    printf("======Third chunk======\n");
    printf("after free: ((void *) lp = %p , (void *) (lp)->limit = %p \n", (void *) (string_obstack)->chunk, (void *) (string_obstack)->chunk->limit);
    printf("after free : prv = %p\n", string_obstack->chunk->prev);


    // Step 4: allocate the third chunk in the location of chunk2
    char *sss = (char *) obstack_alloc (string_obstack, 4064);


    printf("after free : address of s = %p\n", s);
    printf("after free : address of ss = %p\n", ss);
    printf("after free : address of sss = %p\n\n", sss);

    return 0;
}