Mon 14 Oct 23:06:38 CEST 2024

kernel/kmalloc.c

@@ -0,0 +1,225 @@
+/*
+Copyright (C) 2016-2019 The University of Notre Dame
+This software is distributed under the GNU General Public License.
+See the file LICENSE for details.
+*/
+
+#include "kmalloc.h"
+#include "console.h"
+#include "kernel/types.h"
+#include "memorylayout.h"
+
+#define KUNIT sizeof(struct kmalloc_chunk)
+
+#define KMALLOC_STATE_FREE 0xa1a1a1a1
+#define KMALLOC_STATE_USED 0xbfbfbfbf
+
+struct kmalloc_chunk {
+	int state;
+	int length;
+	struct kmalloc_chunk *next;
+	struct kmalloc_chunk *prev;
+};
+
+static struct kmalloc_chunk *head = 0;
+
+/*
+Initialize the linked list by creating a single chunk at
+a given start address and length.  The chunk is initially
+free and has no next or previous chunks.
+*/
+
+void kmalloc_init(char *start, int length)
+{
+	head = (struct kmalloc_chunk *) start;
+	head->state = KMALLOC_STATE_FREE;
+	head->length = length;
+	head->next = 0;
+	head->prev = 0;
+}
+
+/*
+Split a large chunk into two, such that the current chunk
+has the desired length, and the next chunk has the remainder.
+*/
+
+static void ksplit(struct kmalloc_chunk *c, int length)
+{
+	struct kmalloc_chunk *n = (struct kmalloc_chunk *) ((char *) c + length);
+
+	n->state = KMALLOC_STATE_FREE;
+	n->length = c->length - length;
+	n->prev = c;
+	n->next = c->next;
+
+	if(c->next)
+		c->next->prev = n;
+
+	c->next = n;
+	c->length = length;
+}
+
+/*
+Allocate a chunk of memory of the given length.
+To avoid fragmentation, round up the length to
+a multiple of the chunk size.  Then, search fo
+a chunk of the desired size, and split it if necessary.
+*/
+
+void *kmalloc(int length)
+{
+	// round up length to a multiple of KUNIT
+	int extra = length % KUNIT;
+	if(extra)
+		length += (KUNIT - extra);
+
+	// then add one more unit to accommodate the chunk header
+	length += KUNIT;
+
+	struct kmalloc_chunk *c = head;
+
+	while(1) {
+		if(!c) {
+			printf("kmalloc: out of memory!\n");
+			return 0;
+		}
+		if(c->state == KMALLOC_STATE_FREE && c->length >= length)
+			break;
+		c = c->next;
+	}
+
+	// split the chunk if the remainder is greater than two units
+	if((c->length-length) > 2 * KUNIT) {
+		ksplit(c, length);
+	}
+
+	c->state = KMALLOC_STATE_USED;
+
+	// return a pointer to the memory following the chunk header
+	return (c + 1);
+}
+
+/*
+Attempt to merge a chunk with its successor,
+if it exists and both are in the free state.
+*/
+
+static void kmerge(struct kmalloc_chunk *c)
+{
+	if(!c)
+		return;
+
+	if(c->state != KMALLOC_STATE_FREE)
+		return;
+
+	if(c->next && c->next->state == KMALLOC_STATE_FREE) {
+		c->length += c->next->length;
+		if(c->next->next) {
+			c->next->next->prev = c;
+		}
+		c->next = c->next->next;
+	}
+
+}
+
+/*
+Free memory by marking the chunk as de-allocated,
+then attempting to merge it with the predecessor and successor.
+*/
+
+void kfree(void *ptr)
+{
+	struct kmalloc_chunk *c = (struct kmalloc_chunk *) ptr;
+	c--;
+
+	if(c->state != KMALLOC_STATE_USED) {
+		printf("invalid kfree(%x)\n", ptr);
+		return;
+	}
+
+	c->state = KMALLOC_STATE_FREE;
+
+	kmerge(c);
+	kmerge(c->prev);
+}
+
+void kmalloc_debug()
+{
+	struct kmalloc_chunk *c;
+
+	printf("state ptr      prev     next     length\n");
+
+	for(c = head; c; c = c->next) {
+		if(c->state == KMALLOC_STATE_FREE) {
+			printf("F");
+		} else if(c->state == KMALLOC_STATE_USED) {
+			printf("U");
+		} else {
+			printf("kmalloc list corrupted at %x!\n", c);
+			return;
+		}
+		printf("     %x %x %x %d\n", c, c->prev, c->next, c->length);
+	}
+}
+
+// Testing
+
+static void setup(void)
+{
+	kmalloc_init((char *) KMALLOC_START, KMALLOC_LENGTH);
+}
+
+static void tear_down(void)
+{
+}
+
+static int kmalloc_test_single_alloc(void)
+{
+	char *ptr = kmalloc(128);
+	struct kmalloc_chunk *next = 0;
+	int res = (unsigned long) ptr == (unsigned long) head + sizeof(struct kmalloc_chunk);
+	res &= head->state == KMALLOC_STATE_USED;
+	res &= head->length == 128 + sizeof(struct kmalloc_chunk);
+	res &= (char *) head->next == (char *) KMALLOC_START + head->length;
+	next = head->next;
+	res &= next->state == KMALLOC_STATE_FREE;
+	res &= next->length == KMALLOC_LENGTH - head->length;
+
+	return res;
+}
+
+static int kmalloc_test_single_alloc_and_free(void)
+{
+	char *ptr = kmalloc(128);
+	int res;
+	kfree(ptr);
+	res = head->state == KMALLOC_STATE_FREE;
+	res &= head->next == 0;
+	res &= head->length == KMALLOC_LENGTH;
+
+	return res;
+}
+
+int kmalloc_test(void)
+{
+	int (*tests[]) (void) = {
+	kmalloc_test_single_alloc, kmalloc_test_single_alloc_and_free,};
+
+	int i = 0;
+	for(i = 0; i < sizeof(tests) / sizeof(tests[0]); i++) {
+		printf("running test %d...", i);
+		int res;
+
+		setup();
+		res = tests[i] ();
+		tear_down();
+
+		if(!res) {
+			printf("failed\n");
+			printf("\ntest %d failed.\n");
+			return 0;
+		}
+		printf("succeeded\n");
+	}
+	return 1;
+}