myMalloc.c

#define _DEFAULT_SOURCE
#include <sys/mman.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "myMalloc.h"

Block *head = NULL;

void *my_malloc(size_t size) 
{
    if (size == 0) 
    {
        printf("\nError: size 0 is not valid\n");
        return NULL;
    }

    size_t totalSize = (size + sizeof(Block) + 7) & ~7;

    void *ptr = mmap(NULL, totalSize, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);

    if (ptr == MAP_FAILED) 
    {
        printf("\nError: could not allocate memory with mmap\n");
        return NULL;
    }

    Block *newBlock = (Block *)ptr;
    newBlock->free = 0;
    newBlock->size = size;
    newBlock->next = NULL;

    printf("\nBlock allocated at: %p, requested size: %zu\n", (void *)newBlock, size);

    if (head == NULL) 
    {
        head = newBlock;
    } 
    else 
    {
        Block *aux = head;
        while (aux->next != NULL) 
        {
            aux = aux->next;
        }
        aux->next = newBlock;
    }

    return (void *)(newBlock + 1);
}

void my_free(void *ptr)
{
    if (!ptr) {
        return;
    }

    Block *block = (Block *)ptr - 1;
    size_t totalSize = block->size + sizeof(Block);

    if (block == head) {
        head = block->next;
    } else {
        Block *aux = head;
        while (aux && aux->next != block) {
            aux = aux->next;
        }

        if (aux) {
            aux->next = block->next;
        }
    }

    block->next = NULL;

    if (munmap(block, totalSize) == -1) {
        perror("Error when freeing memory with munmap");
    } else {
        printf("Block successfully freed at: %p\n", (void *)block);
    }
}