source: mainline/uspace/lib/libc/generic/malloc.c@ 88d653c

/*
 * Copyright (c) 2009 Martin Decky
 * Copyright (c) 2009 Petr Tuma
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup libc
 * @{
 */
/** @file
 */

#include <malloc.h>
#include <bool.h>
#include <as.h>
#include <align.h>
#include <macros.h>
#include <assert.h>
#include <errno.h>
#include <bitops.h>
#include <mem.h>
#include <adt/gcdlcm.h>

/* Magic used in heap headers. */
#define HEAP_BLOCK_HEAD_MAGIC  0xBEEF0101

/* Magic used in heap footers. */
#define HEAP_BLOCK_FOOT_MAGIC  0xBEEF0202

/** Allocation alignment (this also covers the alignment of fields
    in the heap header and footer) */
#define BASE_ALIGN  16

/**
 * Either 4 * 256M on 32-bit architecures or 16 * 256M on 64-bit architectures
 */
#define MAX_HEAP_SIZE  (sizeof(uintptr_t) << 28)

/**
 *
 */
#define STRUCT_OVERHEAD  (sizeof(heap_block_head_t) + sizeof(heap_block_foot_t))

/**
 * Calculate real size of a heap block (with header and footer)
 */
#define GROSS_SIZE(size)  ((size) + STRUCT_OVERHEAD)

/**
 * Calculate net size of a heap block (without header and footer)
 */
#define NET_SIZE(size)  ((size) - STRUCT_OVERHEAD)


/** Header of a heap block
 *
 */
typedef struct {
        /* Size of the block (including header and footer) */
        size_t size;
        
        /* Indication of a free block */
        bool free;
        
        /* A magic value to detect overwrite of heap header */
        uint32_t magic;
} heap_block_head_t;

/** Footer of a heap block
 *
 */
typedef struct {
        /* Size of the block (including header and footer) */
        size_t size;
        
        /* A magic value to detect overwrite of heap footer */
        uint32_t magic;
} heap_block_foot_t;

/** Linker heap symbol */
extern char _heap;

/** Address of heap start */
static void *heap_start = 0;

/** Address of heap end */
static void *heap_end = 0;

/** Maximum heap size */
static size_t max_heap_size = (size_t) -1;

/** Current number of pages of heap area */
static size_t heap_pages = 0;

/** Initialize a heap block
 *
 * Fills in the structures related to a heap block.
 *
 * @param addr Address of the block.
 * @param size Size of the block including the header and the footer.
 * @param free Indication of a free block.
 *
 */
static void block_init(void *addr, size_t size, bool free)
{
        /* Calculate the position of the header and the footer */
        heap_block_head_t *head = (heap_block_head_t *) addr;
        heap_block_foot_t *foot =
            (heap_block_foot_t *) (addr + size - sizeof(heap_block_foot_t));
        
        head->size = size;
        head->free = free;
        head->magic = HEAP_BLOCK_HEAD_MAGIC;
        
        foot->size = size;
        foot->magic = HEAP_BLOCK_FOOT_MAGIC;
}

/** Check a heap block
 *
 * Verifies that the structures related to a heap block still contain
 * the magic constants. This helps detect heap corruption early on.
 *
 * @param addr Address of the block.
 *
 */
static void block_check(void *addr)
{
        heap_block_head_t *head = (heap_block_head_t *) addr;
        
        assert(head->magic == HEAP_BLOCK_HEAD_MAGIC);
        
        heap_block_foot_t *foot =
            (heap_block_foot_t *) (addr + head->size - sizeof(heap_block_foot_t));
        
        assert(foot->magic == HEAP_BLOCK_FOOT_MAGIC);
        assert(head->size == foot->size);
}

static bool grow_heap(size_t size)
{
        if (size == 0)
                return false;
        
        size_t heap_size = (size_t) (heap_end - heap_start);
        
        if ((max_heap_size != (size_t) -1) && (heap_size + size > max_heap_size))
                return false;
        
        size_t pages = (size - 1) / PAGE_SIZE + 1;
        
        if (as_area_resize((void *) &_heap, (heap_pages + pages) * PAGE_SIZE, 0)
            == EOK) {
                void *end = (void *) ALIGN_DOWN(((uintptr_t) &_heap) +
                    (heap_pages + pages) * PAGE_SIZE, BASE_ALIGN);
                block_init(heap_end, end - heap_end, true);
                heap_pages += pages;
                heap_end = end;
                return true;
        }
        
        return false;
}

static void shrink_heap(void)
{
        // TODO
}

/** Initialize the heap allocator
 *
 * Finds how much physical memory we have and creates
 * the heap management structures that mark the whole
 * physical memory as a single free block.
 *
 */
void __heap_init(void)
{
        if (as_area_create((void *) &_heap, PAGE_SIZE,
            AS_AREA_WRITE | AS_AREA_READ)) {
                heap_pages = 1;
                heap_start = (void *) ALIGN_UP((uintptr_t) &_heap, BASE_ALIGN);
                heap_end =
                    (void *) ALIGN_DOWN(((uintptr_t) &_heap) + PAGE_SIZE, BASE_ALIGN);
                
                /* Make the entire area one large block. */
                block_init(heap_start, heap_end - heap_start, true);
        }
}

uintptr_t get_max_heap_addr(void)
{
        if (max_heap_size == (size_t) -1)
                max_heap_size =
                    max((size_t) (heap_end - heap_start), MAX_HEAP_SIZE);
        
        return ((uintptr_t) heap_start + max_heap_size);
}

static void split_mark(heap_block_head_t *cur, const size_t size)
{
        assert(cur->size >= size);
        
        /* See if we should split the block. */
        size_t split_limit = GROSS_SIZE(size);
        
        if (cur->size > split_limit) {
                /* Block big enough -> split. */
                void *next = ((void *) cur) + size;
                block_init(next, cur->size - size, true);
                block_init(cur, size, false);
        } else {
                /* Block too small -> use as is. */
                cur->free = false;
        }
}

/** Allocate a memory block
 *
 * @param size  The size of the block to allocate.
 * @param align Memory address alignment.
 *
 * @return the address of the block or NULL when not enough memory.
 *
 */
static void *malloc_internal(const size_t size, const size_t align)
{
        if (align == 0)
                return NULL;
        
        size_t falign = lcm(align, BASE_ALIGN);
        size_t real_size = GROSS_SIZE(ALIGN_UP(size, falign));
        
        bool grown = false;
        void *result;
        
loop:
        result = NULL;
        heap_block_head_t *cur = (heap_block_head_t *) heap_start;
        
        while ((result == NULL) && ((void *) cur < heap_end)) {
                block_check(cur);
                
                /* Try to find a block that is free and large enough. */
                if ((cur->free) && (cur->size >= real_size)) {
                        /* We have found a suitable block.
                           Check for alignment properties. */
                        void *addr = ((void *) cur) + sizeof(heap_block_head_t);
                        void *aligned = (void *) ALIGN_UP(addr, falign);
                        
                        if (addr == aligned) {
                                /* Exact block start including alignment. */
                                split_mark(cur, real_size);
                                result = addr;
                        } else {
                                /* Block start has to be aligned */
                                size_t excess = (size_t) (aligned - addr);
                                
                                if (cur->size >= real_size + excess) {
                                        /* The current block is large enough to fit
                                           data in including alignment */
                                        if ((void *) cur > heap_start) {
                                                /* There is a block before the current block.
                                                   This previous block can be enlarged to compensate
                                                   for the alignment excess */
                                                heap_block_foot_t *prev_foot =
                                                    ((void *) cur) - sizeof(heap_block_foot_t);
                                                
                                                heap_block_head_t *prev_head =
                                                    (heap_block_head_t *) (((void *) cur) - prev_foot->size);
                                                
                                                block_check(prev_head);
                                                
                                                size_t reduced_size = cur->size - excess;
                                                heap_block_head_t *next_head = ((void *) cur) + excess;
                                                
                                                if ((!prev_head->free) && (excess >= STRUCT_OVERHEAD)) {
                                                        /* The previous block is not free and there is enough
                                                           space to fill in a new free block between the previous
                                                           and current block */
                                                        block_init(cur, excess, true);
                                                } else {
                                                        /* The previous block is free (thus there is no need to
                                                           induce additional fragmentation to the heap) or the
                                                           excess is small, thus just enlarge the previous block */
                                                        block_init(prev_head, prev_head->size + excess, prev_head->free);
                                                }
                                                
                                                block_init(next_head, reduced_size, true);
                                                split_mark(next_head, real_size);
                                                result = aligned;
                                                cur = next_head;
                                        } else {
                                                /* The current block is the first block on the heap.
                                                   We have to make sure that the alignment excess
                                                   is large enough to fit a new free block just
                                                   before the current block */
                                                while (excess < STRUCT_OVERHEAD) {
                                                        aligned += falign;
                                                        excess += falign;
                                                }
                                                
                                                /* Check for current block size again */
                                                if (cur->size >= real_size + excess) {
                                                        size_t reduced_size = cur->size - excess;
                                                        cur = (heap_block_head_t *) (heap_start + excess);
                                                        
                                                        block_init(heap_start, excess, true);
                                                        block_init(cur, reduced_size, true);
                                                        split_mark(cur, real_size);
                                                        result = aligned;
                                                }
                                        }
                                }
                        }
                }
                
                /* Advance to the next block. */
                cur = (heap_block_head_t *) (((void *) cur) + cur->size);
        }
        
        if ((result == NULL) && (!grown)) {
                if (grow_heap(real_size)) {
                        grown = true;
                        goto loop;
                }
        }
        
        return result;
}

void *malloc(const size_t size)
{
        return malloc_internal(size, BASE_ALIGN);
}

void *memalign(const size_t align, const size_t size)
{
        if (align == 0)
                return NULL;
        
        size_t palign =
            1 << (fnzb(max(sizeof(void *), align) - 1) + 1);
        
        return malloc_internal(size, palign);
}

void *realloc(const void *addr, const size_t size)
{
        if (addr == NULL)
                return malloc(size);
        
        /* Calculate the position of the header. */
        heap_block_head_t *head =
            (heap_block_head_t *) (addr - sizeof(heap_block_head_t));
        
        assert((void *) head >= heap_start);
        assert((void *) head < heap_end);
        
        block_check(head);
        assert(!head->free);
        
        void *ptr = NULL;
        size_t real_size = GROSS_SIZE(ALIGN_UP(size, BASE_ALIGN));
        size_t orig_size = head->size;
        
        if (orig_size > real_size) {
                /* Shrink */
                if (orig_size - real_size >= STRUCT_OVERHEAD) {
                        /* Split the original block to a full block
                           and a tailing free block */
                        block_init((void *) head, real_size, false);
                        block_init((void *) head + real_size,
                            orig_size - real_size, true);
                        shrink_heap();
                }
                
                ptr = ((void *) head) + sizeof(heap_block_head_t);
        } else {
                /* Look at the next block. If it is free and the size is
                   sufficient then merge the two. */
                heap_block_head_t *next_head =
                    (heap_block_head_t *) (((void *) head) + head->size);
                
                if (((void *) next_head < heap_end) &&
                    (head->size + next_head->size >= real_size) &&
                    (next_head->free)) {
                        block_check(next_head);
                        block_init(head, head->size + next_head->size, false);
                        split_mark(head, real_size);
                        
                        ptr = ((void *) head) + sizeof(heap_block_head_t);
                } else {
                        ptr = malloc(size);
                        if (ptr != NULL) {
                                memcpy(ptr, addr, NET_SIZE(orig_size));
                                free(addr);
                        }
                }
        }
        
        return ptr;
}

/** Free a memory block
 *
 * @param addr The address of the block.
 */
void free(const void *addr)
{
        /* Calculate the position of the header. */
        heap_block_head_t *head
            = (heap_block_head_t *) (addr - sizeof(heap_block_head_t));
        
        assert((void *) head >= heap_start);
        assert((void *) head < heap_end);
        
        block_check(head);
        assert(!head->free);
        
        /* Mark the block itself as free. */
        head->free = true;
        
        /* Look at the next block. If it is free, merge the two. */
        heap_block_head_t *next_head
            = (heap_block_head_t *) (((void *) head) + head->size);
        
        if ((void *) next_head < heap_end) {
                block_check(next_head);
                if (next_head->free)
                        block_init(head, head->size + next_head->size, true);
        }
        
        /* Look at the previous block. If it is free, merge the two. */
        if ((void *) head > heap_start) {
                heap_block_foot_t *prev_foot =
                    (heap_block_foot_t *) (((void *) head) - sizeof(heap_block_foot_t));
                
                heap_block_head_t *prev_head =
                    (heap_block_head_t *) (((void *) head) - prev_foot->size);
                
                block_check(prev_head);
                
                if (prev_head->free)
                        block_init(prev_head, prev_head->size + head->size, true);
        }
        
        shrink_heap();
}

/** @}
 */