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141 lines
3.7 KiB
141 lines
3.7 KiB
/*
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* Yet Another Malloc
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* yamalloc.c
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*/
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/*---------------------*/
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/* Feature test macros */
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/*---------------------*/
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#define _DEFAULT_SOURCE // for sbrk
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/*----------*/
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/* Includes */
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/*----------*/
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#include <unistd.h>
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#include <stdio.h>
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#include <stdbool.h>
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#include "yamalloc.h"
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#include "ya_debug.h"
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#include "ya_block.h"
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/*-----------*/
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/* Constants */
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/*-----------*/
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/*--------*/
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/* Macros */
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/*--------*/
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/*--------------------*/
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/* Local declarations */
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/*--------------------*/
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/*----------------------*/
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/* Function definitions */
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/*----------------------*/
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#ifdef YA_DEBUG
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/* Print all blocks in the heap */
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void ya_print_blocks() {
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block_print_range(heap_start, heap_end);
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}
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#endif
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/* Allocates enough memory to store at least size bytes.
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* Returns a dword-aligned pointer to the memory or NULL in case of failure. */
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void *malloc(size_t n_bytes) {
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if (n_bytes == 0) {
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return NULL;
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}
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if (heap_start == NULL || heap_end == NULL) {
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if (!heap_init()) {
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return NULL;
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}
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}
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intptr_t min_size = block_fit(n_bytes);
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intptr_t *block = block_find(min_size);
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block_split(block, min_size);
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block_alloc(block);
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return block;
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}
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/* Frees the memory block pointed to by ptr, which must have been allocated
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* through a call to malloc, calloc or realloc before. Otherwise, undefined
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* behavior occurs. */
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void free(void *ptr) {
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intptr_t *block = ptr;
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if (block < heap_start || block > heap_end || !block_is_alloc(block)) {
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return; // TODO: provoke segfault
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}
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block_free(block);
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block_join(block);
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}
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/* Allocates enough memory to store an array of nmemb elements,
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* each size bytes large, and clears the memory.
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* Returns the pointer to the allocated memory or NULL in case of failure. */
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void *calloc(size_t nmemb, size_t n_bytes) {
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intptr_t *block = malloc(n_bytes * nmemb);
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intptr_t size = block_size(block);
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block_clear(block);
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return block;
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}
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/* Resizes the previously allocated memory pointed to by ptr to size.
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* If ptr is NULL, it is equivalent to malloc(size).
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* If called with size 0, it is equivalent to free(ptr).
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* If ptr does not point to memory previously allocated by malloc, calloc or
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* realloc, undefined behavior occurs.
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* */
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void *realloc(void *ptr, size_t n_bytes) {
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if (!ptr) {
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return malloc(n_bytes);
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}
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if (n_bytes == 0) {
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free(ptr);
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}
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intptr_t *block = ptr;
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if (block < heap_start) {
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return NULL; // TODO: provoke segfault
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}
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intptr_t new_size = block_fit(n_bytes);
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intptr_t size = block_size(block); // segfault if ptr after heap end
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if (new_size == size) {
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return ptr; // don't change anything
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}
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if (new_size < size) {
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intptr_t *next = block_split(block, new_size);
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if (next) {
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block_join_next(next); // coalesce the leftovers
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}
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block_alloc(block);
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return block;
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}
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intptr_t *next = block + size;
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// try to use next free block
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if (next < heap_end) {
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intptr_t next_size = block_size(next);
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if (!block_is_alloc(next) && new_size <= size + next_size) {
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block_join_next(block); // coalesce
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block_split(block, new_size); // split if possible
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// no need to coalesce
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block_alloc(block); // mark block as allocated
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return block;
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}
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}
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// resizing failed, so allocate a whole new block and copy
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// could handle the case when the block is the last in the heap
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// a bit more gracefully and just grow the heap instead of copying
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intptr_t *new_block = malloc(n_bytes);
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for (int i = 0; i < size; i++) {
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new_block[i] = block[i];
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}
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free(block);
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return new_block;
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}
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