/* Return a block of at least size bytes, or NULL if no such block
can be found. */
void *malloc(size_t size) {
void *heap_end, *heap_end_p;
free_block_t *block;
free_block_t **prev_p; /* Previous link so we can remove an element */
if (size == 0) {
return NULL;
}
/* Add space for bookkeeping. */
size += sizeof(free_block_t);
/* Word-align */
if (size % 4 != 0) {
size &= ~3;
size += 4;
}
/* Iterate through list of free blocks, using the first that is
big enough for the request. */
for (block = free_list, prev_p = &free_list;
block;
prev_p = &(block->next), block = block->next) {
if ( (int)( block->size - size ) >=
(int)( MIN_ALLOC_SIZE+sizeof(free_block_t) ) ) {
/* Block is too big, but can be split. */
free_block_t *new_block =
(free_block_t*)(((byte*)block)+size);
new_block->size = block->size - size;
new_block->next = block->next;
block->size = size - sizeof(free_block_t);
*prev_p = new_block;
return ((byte*)block)+sizeof(free_block_t);
} else if (block->size >= size) {
/* Block is big enough, but not so big that we can split
it, so just return it */
*prev_p = block->next;
return ((byte*)block)+sizeof(free_block_t);
}
/* Else, check the next block. */
}
heap_end_p = syscall_memlimit(NULL);
heap_end = syscall_memlimit((void*)((int)heap_end_p + size));
if(heap_end != NULL)
{
block = (free_block_t*)((int)prev_p - sizeof(size_t));
block->size += (int)heap_end - (int)heap_end_p;
return malloc(size);
}
/* No heap space left. */
return NULL;
}
/* Initialise the heap - malloc et al won't work unless this is called
first. */
void heap_init()
{
void* heap_end;
free_list = syscall_memlimit(NULL);
/* Ew, casting-magic - increment with 1 instead of sizeof(free_block_t) */
free_list = (free_block_t*) ((uint32_t)free_list + 1);
heap_end = syscall_memlimit(free_list);
free_list->size = (int)heap_end - (int)free_list + 1 - sizeof(free_block_t);
free_list->next = NULL;
}
/* Return a block of at least size bytes, or NULL if no such block
can be found. */
void *malloc(size_t size) {
free_block_t *block;
free_block_t **prev_p; /* Previous link so we can remove an element */
if (size == 0) {
return NULL;
}
/* Ensure block is big enough for bookkeeping. */
size=MAX(MIN_ALLOC_SIZE,size);
/* Iterate through list of free blocks, using the first that is
big enough for the request. */
for (block = free_list, prev_p = &free_list;
block;
prev_p = &(block->next), block = block->next) {
if ( (int)( block->size - size - sizeof(size_t) ) >=
(int)( MIN_ALLOC_SIZE+sizeof(size_t) ) ) {
/* Block is too big, but can be split. */
block->size -= size+sizeof(size_t);
free_block_t *new_block =
(free_block_t*)(((byte*)block)+block->size);
new_block->size = size+sizeof(size_t);
return ((byte*)new_block)+sizeof(size_t);
} else if (block->size >= size + sizeof(size_t)) {
/* Block is big enough, but not so big that we can split
it, so just return it */
*prev_p = block->next;
return ((byte*)block)+sizeof(size_t);
}
/* Else, check the next block. */
}
/* No suitable free block was found, increase heap size. */
void *heap_end = syscall_memlimit(NULL);
void *new_heap_end = syscall_memlimit(heap_end+size+sizeof(size_t));
if(new_heap_end - heap_end - size - sizeof(size_t) == 0) {
block = (free_block_t *)heap_end;
block->size = size + sizeof(size_t);
return ((byte*)block)+sizeof(size_t);
} else {
/* Heap could not be increased sufficiently, set it back. */
syscall_memlimit(heap_end);
}
/* No heap space left. */
return NULL;
}
/* Return a block of at least size bytes, or NULL if no such block
can be found. */
void *malloc(unsigned int size) {
free_block_t *block;
free_block_t **prev_p; /* Previous link so we can remove an element */
void* heap_ptr;
int free_size;
if (size == 0) {
return NULL;
}
heap_ptr = syscall_memlimit(NULL);
printf("heap_ptr = %d \n",(int) heap_ptr);
/* Ensure block is big enough for bookkeeping. */
size=MAX(MIN_ALLOC_SIZE,size);
/* Word-align */
if (size % 4 != 0) {
size &= ~3;
size += 4;
}
/* Iterate through list of free blocks, using the first that is
big enough for the request. */
for (block = free_list, prev_p = &free_list; block; prev_p = &(block->next), block = block->next) {
if ( (int)( block->size - size - sizeof(size_t) ) >= (int)( MIN_ALLOC_SIZE+sizeof(size_t) ) ) {
/* Block is too big, but can be split. */
block->size -= size+sizeof(size_t);
free_block_t *new_block = (free_block_t*) (((byte*)block)+block->size);
new_block->size = size+sizeof(size_t);
return ((byte*)new_block)+sizeof(size_t);
} else if (block->size >= size + sizeof(size_t)) {
/* Block is big enough, but not so big that we can split
it, so just return it */
*prev_p = block->next;
return ((byte*)block)+sizeof(size_t);
}
/* Else, check the next block. */
}
free_block_t* free_block = (free_block_t*) syscall_memlimit(heap_ptr + size + MIN_ALLOC_SIZE);
if ((free_size = size % 4096) != 0) {
free_block->size = free_size;
free_block->next = free_list;
free_list = free_block;
}
free_block_t* return_block = (free_block_t*) heap_ptr;
return_block->size = size + MIN_ALLOC_SIZE;
return heap_ptr + MIN_ALLOC_SIZE;
}
int main() {
char* a_string;
/* Find the current (initial) heap end. */
a_string = syscall_memlimit(NULL);
/* Extend the heap, and check that it worked. */
if (syscall_memlimit(a_string + STRING_LENGTH) == NULL) {
/* It didn't work, so exit already. */
return 1;
}
/* Copy the source string to the dynamically allocated memory. */
for (size_t i = 0; i < STRING_LENGTH; i++) {
a_string[i] = STRING_SOURCE[i];
}
/* Write from the dynamically allocated memory. */
syscall_write(1, a_string, STRING_LENGTH);
return 0;
}
/* Return the block pointed to by ptr to the free pool. */
void free(void *ptr)
{
if (ptr != NULL) { /* Freeing NULL is a no-op */
free_block_t *block = (free_block_t*)((byte*)ptr-sizeof(free_block_t));
free_block_t *cur_block;
free_block_t *prev_block;
printf("free_list: %8.8x\nheap_end: %8.8x\nblock: %8.8x\n", (uint32_t)free_list, (uint32_t)syscall_memlimit(NULL), (uint32_t)block);
/* Iterate through the free list, which is sorted by
increasing address, and insert the newly freed block at the
proper position. */
for (cur_block = free_list, prev_block = NULL;
;
prev_block = cur_block, cur_block = cur_block->next) {
if (cur_block > block || cur_block == NULL) {
/* Insert block here. */
if (prev_block == NULL) {
free_list = block;
} else {
prev_block->next = block;
}
printf("cur_block = %8.8x\n", (uint32_t)cur_block);
block->next = cur_block;
if (prev_block != NULL &&
(size_t)((byte*)block - (byte*)prev_block) == prev_block->size + sizeof(free_block_t)) {
/* Merge with previous. */
prev_block->size += block->size + sizeof(free_block_t);
prev_block->next = cur_block;
block = prev_block;
}
if (cur_block != NULL &&
(size_t)((byte*)cur_block - (byte*)block) == block->size + sizeof(free_block_t)) {
/* Merge with next. */
block->size += cur_block->size + sizeof(free_block_t);
block->next = cur_block->next;
}
return;
}
}
}
}
/* Return a block of at least size bytes, or NULL if no such block
can be found. */
void *malloc(size_t size) {
free_block_t *block;
free_block_t **prev_p; /* Previous link so we can remove an element */
void *old_end, *new_end;
free_block_t *new_block, *tmp;
if (size == 0) {
return NULL;
}
if (mallptrs_size >= MAX_MALL_PTRS) {
printf("Malloc: mallptrs array is filled up%s\n","");
return NULL;
}
/* Ensure block is big enough for bookkeeping. */
size=MAX(MIN_ALLOC_SIZE,size);
/* Word-align */
if (size % 4 != 0) {
size &= ~3;
size += 4;
}
/* Iterate through list of free blocks, using the first that is
big enough for the request. */
for (block = free_list, prev_p = &free_list;
block;
prev_p = &(block->next), block = block->next) {
printf("Malloc: Free-list block: pointer %d, size %d, next %d\n"
,(uint32_t)block,block->size,(block->next != NULL));
if ( (int)( block->size - size - sizeof(size_t) ) >=
(int)( MIN_ALLOC_SIZE+sizeof(size_t) ) ) {
/* Block is too big, but can be split. */
block->size -= size+sizeof(size_t);
free_block_t *new_block =
(free_block_t*)(((byte*)block)+block->size);
new_block->size = size+sizeof(size_t);
/*return ((byte*)new_block)+sizeof(size_t);*/
return mallptrs_insert(((byte*)new_block)+sizeof(size_t));
} else if (block->size >= size + sizeof(size_t)) {
/* Block is big enough, but not so big that we can split
it, so just return it */
*prev_p = block->next;
/*return ((byte*)block)+sizeof(size_t);*/
return mallptrs_insert(((byte*)block)+sizeof(size_t));
}
/* Else, check the next block. */
}
/* If no suitable free block was found, we must
allocate a new one. */
/* If this is the first time, we get the addresse of
our process's heap end, for bookkeeping.
And initialize the mallptrs array. */
if (heap_start == NULL) {
heap_start = syscall_memlimit(NULL);
heap_end = heap_start;
mallptrs_init();
printf("Malloc: Heap_start: %d\n", (uint32_t)heap_start);
}
printf("Malloc: Size: %d, heapend: %d\n", size, (uint32_t)heap_end);
old_end = heap_end;
heap_end = (void*)((uint32_t)heap_end + size+ sizeof(size_t));
/* Try and allocate more memory */
new_end = syscall_memlimit(heap_end);
/* Check if it was possible to get more memory. */
if(new_end == NULL){
/* No heap space left. */
printf("Malloc: syscall_memlimit returned NULL%s\n","");
heap_end = (void*)((uint32_t)heap_end - size+ sizeof(size_t));
return NULL;
}
printf("Malloc: memlimit returned %d\n", (uint32_t)new_end);
/* Make sure that the new end is not lower than what
the user requested. */
if(new_end < heap_end) {
printf("Malloc: new_end (%d) was lower than what was requested (%d)\n"
,(uint32_t)new_end,(uint32_t)heap_end);
return NULL;
}
/* Make sure the new end is not lower than the old.
It should not happen. */
if(old_end >= new_end) {
printf("Malloc: new_end was lower or equal to the old_end%s\n","");
heap_end = (void*)((uint32_t)heap_end - size+ sizeof(size_t));
return NULL;
}
/* Create a new free block with the size we just allocated. */
new_block = (free_block_t*)((byte*)old_end);
new_block->size = new_end - old_end;
new_block->next = NULL;
printf("Malloc: Created free block with size %d and address %d\n",new_block->size, (uint32_t)new_block);
/* Attach it too the list of free blocks in a
sorted manor. That is at the end. */
if (free_list == NULL) {
printf("Malloc: free_list is null%s\n","");
free_list = new_block;
} else {
printf("Malloc: free_list is not null%s\n","");
tmp = free_list;
while (tmp->next != NULL) {
tmp = tmp->next;
}
tmp->next = new_block;
printf("Malloc: out of loop%s\n","");
}
/* Update the heap end to the new end address. */
heap_end = new_end;
/* Recursively call malloc which should now find the free block
we just created and fullfill the user request for more memory. */
return malloc(size);
}
/* Return the block pointed to by ptr to the free pool. */
void free(void *ptr) {
if (free != NULL) { /* Freeing NULL is a no-op */
free_block_t *block = (free_block_t*)((byte*)ptr-sizeof(size_t));
free_block_t *cur_block;
free_block_t *prev_block;
free_block_t *prev_prev_block;
/* Iterate through the free list, which is sorted by
increasing address, and insert the newly freed block at the
proper position. */
for (cur_block = free_list, prev_block = prev_prev_block = NULL;
;
prev_prev_block = prev_block, prev_block = cur_block,
cur_block = cur_block->next) {
if (cur_block > block || cur_block == NULL) {
/* Insert block here. */
if (prev_block == NULL) {
free_list = block;
} else {
prev_block->next = block;
}
block->next = cur_block;
if (prev_block != NULL &&
(size_t)((byte*)block - (byte*)prev_block) == prev_block->size) {
/* Merge with previous. */
prev_block->size += block->size;
prev_block->next = cur_block;
block = prev_block;
}
if (cur_block != NULL &&
(size_t)((byte*)cur_block - (byte*)block) == block->size) {
/* Merge with next. */
block->size += cur_block->size;
block->next = cur_block->next;
}
uint32_t heap = (uint32_t) syscall_memlimit(NULL);
if((uint32_t)block + block->size == heap) {
/* If block is the last on heap, remove block and
decrease heap size. */
if(prev_block == block) {
/* If merged with prev_block, we must update
prev_prev_block. */
if(prev_prev_block == NULL) {
free_list = block->next;
} else {
prev_prev_block->next = block->next;
}
} else {
/* update prev_block. */
if(prev_block == NULL) {
free_list = block->next;
} else {
prev_block->next = block->next;
}
}
syscall_memlimit(block);
}
return;
}
}
}
}