mymalloc.c

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/*
 * Copyright (c) 2002 Joerg Wunsch
 *
 * All rights reserved.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``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 DEVELOPERS 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.
 *
 * $Id: malloc.c,v 1.6 2003/01/08 11:14:10 joerg_wunsch Exp $
 */

#include <stdlib.h>

#include <avr/io.h>

#ifndef __AVR__

/*
 * When compiling this file natively on a host machine, it will
 * include a main() that performs a regression test.  This is meant as
 * a debugging aid, where a normal source-level debugger will help to
 * verify that the various allocator structures have the desired
 * appearance at each stage.
 *
 * When cross-compiling with avr-gcc, it will compile into just the
 * library functions malloc() and free().
 */
#define MALLOC_TEST

#endif /* !__AVR__ */

struct freelist {
	size_t sz;
	struct freelist *nx;
};

#if 0
// ******** originally coded as internal statics
static char *brkval;
static struct freelist *flp;
#else
// Changes thusly to be globally visible
char *brkval;
struct freelist *flp;
#endif

#ifdef MALLOC_TEST

#define malloc mymalloc
#define free myfree
#define __heap_start mymem
#define __heap_end ((char *)0)

char mymem[256];
#define STACK_POINTER() (mymem + 256)

#else /* !MALLOC_TEST */

extern char __heap_start;
extern char __heap_end;

#define STACK_POINTER() ((char *)SP)

#endif /* MALLOC_TEST */

/*
 * Exported interface:
 *
 * When extending the data segment, the allocator will not try to go
 * beyond the current stack limit, decreased by __malloc_margin bytes.
 * Thus, all possible stack frames of interrupt routines that could
 * interrupt the current function, plus all further nested function
 * calls must not require more stack space, or they'll risk to collide
 * with the data segment.
 */
 
/* May be changed by the user only before the first malloc() call.  */

size_t __malloc_margin = 32;
char *__malloc_heap_start = &__heap_start;
char *__malloc_heap_end = &__heap_end;

void *
malloc(size_t len)
{
	struct freelist *fp1, *fp2;
	char *cp;
	size_t s;

	/*
	 * Our minimum chunk size is the size of a pointer (plus the
	 * size of the "sz" field, but we don't need to account for
	 * this), otherwise we could not possibly fit a freelist entry
	 * into the chunk later.
	 */
	if (len < sizeof(struct freelist) - sizeof(size_t))
		len = sizeof(struct freelist) - sizeof(size_t);

	/*
	 * First, walk the free list and try finding a chunk that
	 * would match exactly.  If we found one, we are done.  While
	 * walking, note down the size of the largest chunk we found
	 * that would still fit the request -- we need it for step 2.
	 *
	 */
	for (s = 0, fp1 = flp, fp2 = 0;
	     fp1;
	     fp2 = fp1, fp1 = fp1->nx) {
		if (fp1->sz == len) {
			/*
			 * Found it.  Disconnect the chunk from the
			 * freelist, and return it.
			 */
			if (fp2)
				fp2->nx = fp1->nx;
			else
				flp = fp1->nx;
			return &(fp1->nx);
		}
		if (fp1->sz > len) {
			if (s == 0 || fp1->sz < s)
				s = fp1->sz;
		}
	}
	/*
	 * Step 2: If we found a chunk on the freelist that would fit
	 * (but was too large), look it up again and use it, since it
	 * is our closest match now.  Since the freelist entry needs
	 * to be split into two entries then, watch out that the
	 * difference between the requested size and the size of the
	 * chunk found is large enough for another freelist entry; if
	 * not, just enlarge the request size to what we have found,
	 * and use the entire chunk.
	 */
	if (s) {
		if (s - len < sizeof(struct freelist))
			len = s;
		for (fp1 = flp, fp2 = 0;
		     fp1;
		     fp2 = fp1, fp1 = fp1->nx) {
			if (fp1->sz == s) {
				if (len == s) {
					/*
					 * Use entire chunk; same as
					 * above.
					 */
					if (fp2)
						fp2->nx = fp1->nx;
					else
						flp = fp1->nx;
					return &(fp1->nx);
				}
				/*
				 * Split them up.  Note that we leave
				 * the first part as the new (smaller)
				 * freelist entry, and return the
				 * upper portion to the caller.  This
				 * saves us the work to fix up the
				 * freelist chain; we just need to
				 * fixup the size of the current
				 * entry, and note down the size of
				 * the new chunk before returning it
				 * to the caller.
				 */
				cp = (char *)fp1;
				s -= len;
				cp += s;
				fp2 = (struct freelist *)cp;
				fp2->sz = len;
				fp1->sz = s - sizeof(size_t);
				return &(fp2->nx);
			}
		}
	}
	/*
	 * Step 3: If the request could not be satisfied from a
	 * freelist entry, just prepare a new chunk.  This means we
	 * need to obtain more memory first.  The largest address just
	 * not allocated so far is remembered in the brkval variable.
	 * Under Unix, the "break value" was the end of the data
	 * segment as dynamically requested from the operating system.
	 * Since we don't have an operating system, just make sure
	 * that we don't collide with the stack.
	 */
	if (brkval == 0)
		brkval = __malloc_heap_start;
	cp = __malloc_heap_end;
	if (cp == 0)
		cp = STACK_POINTER() - __malloc_margin;
	if (brkval + len + sizeof(size_t) < cp) {
		fp1 = (struct freelist *)brkval;
		brkval += len + sizeof(size_t);
		fp1->sz = len;
		return &(fp1->nx);
	}
	/*
	 * Step 4: There's no help, just fail. :-/
	 */
	return 0;
}

void
free(void *p)
{
	struct freelist *fp1, *fp2, *fpnew;
	char *cp1, *cp2, *cpnew;

	/* ISO C says free(NULL) must be a no-op */
	if (p == 0)
		return;

	cpnew = p;
	cpnew -= sizeof(size_t);
	fpnew = (struct freelist *)cpnew;
	fpnew->nx = 0;

	/*
	 * Trivial case first: if there's no freelist yet, our entry
	 * will be the only one on it.
	 */
	if (flp == 0) {
		flp = fpnew;
		return;
	}

	/*
	 * Now, find the position where our new entry belongs onto the
	 * freelist.  Try to aggregate the chunk with adjacent chunks
	 * if possible.
	 */
	for (fp1 = flp, fp2 = 0;
	     fp1;
	     fp2 = fp1, fp1 = fp1->nx) {
		if (fp1 < fpnew)
			continue;
		cp1 = (char *)fp1;
		fpnew->nx = fp1;
		if ((char *)&(fpnew->nx) + fpnew->sz == cp1) {
			/* upper chunk adjacent, assimilate it */
			fpnew->sz += fp1->sz + sizeof(size_t);
			fpnew->nx = fp1->nx;
		}
		if (fp2 == 0) {
			/* new head of freelist */
			flp = fpnew;
			return;
		}
		break;
	}
	/*
	 * Note that we get here either if we hit the "break" above,
	 * or if we fell off the end of the loop.  The latter means
	 * we've got a new topmost chunk.  Either way, try aggregating
	 * with the lower chunk if possible.
	 */
	fp2->nx = fpnew;
	cp2 = (char *)&(fp2->nx);
	if (cp2 + fp2->sz == cpnew) {
		/* lower junk adjacent, merge */
		fp2->sz += fpnew->sz + sizeof(size_t);
		fp2->nx = fpnew->nx;
	}
}

#ifdef MALLOC_TEST

#include <stdio.h>
#include <time.h>
#include <unistd.h>

void *handles[32];
size_t sizes[32];


void *
alloc(size_t s)
{
	void *p;

	if ((p = malloc(s)) == 0)
		return 0;
	memset(p, 0xd0, s);
	return p;
}

void
printfreelist(void)
{
	struct freelist *fp1;
	int i;

	if (!flp) {
		printf("no free list\n");
		return;
	}

	for (i = 0, fp1 = flp; fp1; i++, fp1 = fp1->nx) {
		printf("entry %d @ %u: size %u, next ",
		       i, (char *)fp1 - mymem, fp1->sz);
		if (fp1->nx)
			printf("%u\n", (char *)fp1->nx - mymem);
		else
			printf("NULL\n");
	}
}

int
compare(const void *p1, const void *p2)
{
	return *((size_t *)p1) - *((size_t *)p2);
}

void
printalloc(void)
{
	int i, j, k;
	size_t sum, sum2;
	void *sortedhandles[32];
	struct freelist *fp;
	char *cp;

	for (i = j = k = sum = sum2 = 0;
	     i < sizeof handles / sizeof (void *);
	     i++)
		if (sizes[i]) {
			j++;
			sum += sizes[i];
			if (handles[i]) {
				k++;
				sum2 += sizes[i];
			}
		}
	printf("brkval: %d, %d request%s => sum %u bytes "
	       "(actually %d reqs => %u bytes)\n",
	       (char *)brkval - mymem, j, j == 1? "": "s", sum, k, sum2);
	memcpy(sortedhandles, handles, sizeof sortedhandles);
	qsort(sortedhandles, 32, sizeof(void *), compare);
	for (i = j = 0; i < sizeof sortedhandles / sizeof (void *); i++)
		if ((cp = sortedhandles[i])) {
			cp -= sizeof(size_t);
			fp = (struct freelist *)cp;
			printf("block %d @ %u: %u bytes\n",
			       j, (char *)&fp->nx - mymem, fp->sz);
			j++;
		}

}


int
main(void)
{
	int i, j, k, l, m, om, p, f;
	size_t s;

	srand(time(0) ^ getpid());

	for (k = 0; k < 100; k++) {
		memset(handles, 0, sizeof handles);
		memset(sizes, 0, sizeof sizes);

		j = rand() % 16 + 15;
		l = rand() % 80 + 7;

		for (i = s = 0; i < j && s < 256; i++) {
			sizes[i] = rand() % l + 1;
			s += sizes[i];
		}
		j = i;
		for (m = om = 1, p = 1, f = 0; m < 1000; m++) {
			for (i = s = 0; i < j; i++)
				if (handles[i])
					s++;
			if (s == j)
				break;

			if (m / om > 10) {
				p <<= 1;
				p |= 1;
			}

			for (i = 0; i < j; i++)
				if (rand() & p) {
					if (!handles[i] &&
					    (handles[i] = alloc(sizes[i])) == 0)
						f++;
				}
			for (i = 0; i < j; i++)
				if (rand() & 1) {
					free(handles[i]);
					handles[i] = 0;
				}
		}
		if (f)
			printf("%d alloc failure%s total\n",
			       f, f == 1? "": "s");
		printf("After alloc:\n");
		printalloc();
		printfreelist();
		for (i = 0; i < j; i++)
			free(handles[i]);
		printf("After cleanup:\n");
		printfreelist();
	}

	return 0;
}

#endif /* MALLOC_TEST */