path: root/payloads/libpayload/libc/malloc.c

/*
 * This file is part of the libpayload project.
 *
 * Copyright (C) 2008 Advanced Micro Devices, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. 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.
 * 3. 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 AND CONTRIBUTORS ``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 OR CONTRIBUTORS 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.
 */

/*
 * This is a classically weak malloc() implementation. We have a relatively
 * small and static heap, so we take the easy route with an O(N) loop
 * through the tree for every malloc() and free(). Obviously, this doesn't
 * scale past a few hundred KB (if that).
 *
 * We're also susceptible to the usual buffer overrun poisoning, though the
 * risk is within acceptable ranges for this implementation (don't overrun
 * your buffers, kids!).
 */

#include <libpayload.h>

extern char _heap, _eheap;	/* Defined in the ldscript. */

static void *hstart = (void *)&_heap;
static void *hend = (void *)&_eheap;

typedef unsigned int hdrtype_t;

#define MAGIC     (0x2a << 26)
#define FLAG_FREE (1 << 25)
#define FLAG_USED (1 << 24)

#define SIZE(_h) ((_h) & 0xFFFFFF)

#define _HEADER(_s, _f) ((hdrtype_t) (MAGIC | (_f) | ((_s) & 0xFFFFFF)))

#define FREE_BLOCK(_s) _HEADER(_s, FLAG_FREE)
#define USED_BLOCK(_s) _HEADER(_s, FLAG_USED)

#define HDRSIZE (sizeof(hdrtype_t))

#define IS_FREE(_h) (((_h) & (MAGIC | FLAG_FREE)) == (MAGIC | FLAG_FREE))
#define HAS_MAGIC(_h) (((_h) & MAGIC) == MAGIC)

void print_malloc_map(void);

static void setup(void)
{
	int size = (unsigned int)(&_eheap - &_heap) - HDRSIZE;

	*((hdrtype_t *) hstart) = FREE_BLOCK(size);
}

static void *alloc(int len)
{
	hdrtype_t header;
	void *ptr = hstart;

	/* Align the size. */
	len = (len + 3) & ~3;

	if (!len || len > 0xffffff)
		return (void *)NULL;

	/* Make sure the region is setup correctly. */
	if (!HAS_MAGIC(*((hdrtype_t *) ptr)))
		setup();

	/* Find some free space. */
	do {
		header = *((hdrtype_t *) ptr);
		int size = SIZE(header);

		if (!HAS_MAGIC(header) || size == 0)
			halt();

		if (header & FLAG_FREE) {
			if (len <= size) {
				void *nptr = ptr + (HDRSIZE + len);
				int nsize = size - (len + 8);

				/* Mark the block as used. */
				*((hdrtype_t *) ptr) = USED_BLOCK(len);

				/* If there is still room in this block,
				 * then mark it as such.
				 */

				if (nsize > 0)
					*((hdrtype_t *) nptr) =
					    FREE_BLOCK(nsize - 4);

				return (void *)(ptr + HDRSIZE);
			}
		}

		ptr += HDRSIZE + size;

	} while (ptr < hend);

	/* Nothing available. */
	return (void *)NULL;
}

static void _consolidate(void)
{
	void *ptr = hstart;

	while (ptr < hend) {
		void *nptr;
		hdrtype_t hdr = *((hdrtype_t *) ptr);
		unsigned int size = 0;

		if (!IS_FREE(hdr)) {
			ptr += HDRSIZE + SIZE(hdr);
			continue;
		}

		size = SIZE(hdr);
		nptr = ptr + HDRSIZE + SIZE(hdr);

		while (nptr < hend) {
			hdrtype_t nhdr = *((hdrtype_t *) nptr);

			if (!(IS_FREE(nhdr)))
				break;

			size += SIZE(nhdr) + HDRSIZE;

			*((hdrtype_t *) nptr) = 0;

			nptr += (HDRSIZE + SIZE(nhdr));
		}

		*((hdrtype_t *) ptr) = FREE_BLOCK(size);
		ptr = nptr;
	}
}

void free(void *ptr)
{
	hdrtype_t hdr;

	ptr -= HDRSIZE;

	/* Sanity check. */
	if (ptr < hstart || ptr >= hend)
		return;

	hdr = *((hdrtype_t *) ptr);

	/* Not our header (we're probably poisoned). */
	if (!HAS_MAGIC(hdr))
		return;

	/* Double free. */
	if (hdr & FLAG_FREE)
		return;

	*((hdrtype_t *) ptr) = FREE_BLOCK(SIZE(hdr));
	_consolidate();
}

void *malloc(size_t size)
{
	return alloc(size);
}

void *calloc(size_t nmemb, size_t size)
{
	size_t total = nmemb * size;
	void *ptr = alloc(total);

	if (ptr)
		memset(ptr, 0, total);

	return ptr;
}

void *realloc(void *ptr, size_t size)
{
	void *ret, *pptr;
	unsigned int osize;

	if (ptr == NULL)
		return alloc(size);

	pptr = ptr - HDRSIZE;

	if (!HAS_MAGIC(*((hdrtype_t *) pptr)))
		return NULL;

	/* Get the original size of the block. */
	osize = SIZE(*((hdrtype_t *) pptr));

	/*
	 * Free the memory to update the tables - this won't touch the actual
	 * memory, so we can still use it for the copy after we have
	 * reallocated the new space.
	 */
	free(ptr);
	ret = alloc(size);

	/*
	 * if ret == NULL, then doh - failure.
	 * if ret == ptr then woo-hoo! no copy needed.
	 */
	if (ret == NULL || ret == ptr)
		return ret;

	/* Copy the memory to the new location. */
	memcpy(ret, ptr, osize > size ? size : osize);

	return ret;
}

/* This is for debugging purposes. */
#ifdef TEST
void print_malloc_map(void)
{
	void *ptr = hstart;

	while (ptr < hend) {
		hdrtype_t hdr = *((hdrtype_t *) ptr);

		if (!HAS_MAGIC(hdr)) {
			printf("Poisoned magic - we're toast\n");
			break;
		}

		/* FIXME: Verify the size of the block. */

		printf("%x: %s (%x bytes)\n",
		       (unsigned int)(ptr - hstart),
		       hdr & FLAG_FREE ? "FREE" : "USED", SIZE(hdr));

		ptr += HDRSIZE + SIZE(hdr);
	}
}
#endif