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

int main()
{
    fprintf(stderr, "This file doesn't demonstrate an attack, but shows the nature of glibc's allocator.\n");
    fprintf(stderr, "glibc uses a first-fit algorithm to select a free chunk.\n");
    fprintf(stderr, "If a chunk is free and large enough, malloc will select it.\n");
    fprintf(stderr, "The speed of malloc is primarily determined by the length of the bin lists.\n");

    char* a = malloc(0x512);
    char* b = malloc(0x256);
    char* c = malloc(0x256);
    
    // First-fit: a is reused for the 0x500 allocation
    fprintf(stderr, "Allocating 3 chunks of various sizes\n");
    
    free(a);
    free(b);
    free(c);
    
    fprintf(stderr, "Now, let's allocate a chunk of size 0x500\n");
    char *d = malloc(0x500);
    fprintf(stderr, "This chunk has address %p, which is the same as 'a': %p\n", d, a);
}