1 /*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
12 *
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 *
19 * CDDL HEADER END
20 */
21
22 /*
23 * Copyright 2008 Sun Microsystems, Inc. All rights reserved.
24 * Use is subject to license terms.
25 */
26
27 /* Copyright (c) 1988 AT&T */
28 /* All Rights Reserved */
29
30 #pragma ident "%Z%%M% %I% %E% SMI"
31
32 #include "lint.h"
33 #include "mallint.h"
34 #include "mtlib.h"
35
36 #define _misaligned(p) ((unsigned)(p) & 3)
37 /* 4-byte "word" alignment is considered ok in LP64 */
38 #define _nextblk(p, size) ((TREE *)((uintptr_t)(p) + (size)))
39
40 /*
41 * memalign(align, nbytes)
42 *
43 * Description:
44 * Returns a block of specified size on a specified alignment boundary.
45 *
46 * Algorithm:
47 * Malloc enough to ensure that a block can be aligned correctly.
48 * Find the alignment point and return the fragments
49 * before and after the block.
50 *
51 * Errors:
52 * Returns NULL and sets errno as follows:
53 * [EINVAL]
54 * if nbytes = 0,
55 * or if alignment is misaligned,
56 * or if the heap has been detectably corrupted.
57 * [ENOMEM]
58 * if the requested memory could not be allocated.
59 */
60
61 void *
memalign(size_t align,size_t nbytes)62 memalign(size_t align, size_t nbytes)
63 {
64 size_t reqsize; /* Num of bytes to get from malloc() */
65 TREE *p; /* Ptr returned from malloc() */
66 TREE *blk; /* For addressing fragment blocks */
67 size_t blksize; /* Current (shrinking) block size */
68 TREE *alignedp; /* Ptr to properly aligned boundary */
69 TREE *aligned_blk; /* The block to be returned */
70 size_t frag_size; /* size of fragments fore and aft */
71 size_t x;
72
73 if (!primary_link_map) {
74 errno = ENOTSUP;
75 return (NULL);
76 }
77
78 /*
79 * check for valid size and alignment parameters
80 * MAX_ALIGN check prevents overflow in later calculation.
81 */
82 if (nbytes == 0 || _misaligned(align) || align == 0 ||
83 align > MAX_ALIGN) {
84 errno = EINVAL;
85 return (NULL);
86 }
87
88 /*
89 * Malloc enough memory to guarantee that the result can be
90 * aligned correctly. The worst case is when malloc returns
91 * a block so close to the next alignment boundary that a
92 * fragment of minimum size cannot be created. In order to
93 * make sure we can handle this, we need to force the
94 * alignment to be at least as large as the minimum frag size
95 * (MINSIZE + WORDSIZE).
96 */
97
98 /* check for size that could overflow calculations */
99 if (nbytes > MAX_MALLOC) {
100 errno = ENOMEM;
101 return (NULL);
102 }
103 ROUND(nbytes);
104 if (nbytes < MINSIZE)
105 nbytes = MINSIZE;
106 ROUND(align);
107 while (align < MINSIZE + WORDSIZE)
108 align <<= 1;
109 reqsize = nbytes + align + (MINSIZE + WORDSIZE);
110
111 /* check for overflow */
112 if (reqsize < nbytes) {
113 errno = ENOMEM;
114 return (NULL);
115 }
116
117 p = (TREE *)malloc(reqsize);
118 if (p == (TREE *)NULL) {
119 /* malloc sets errno */
120 return (NULL);
121 }
122 (void) mutex_lock(&libc_malloc_lock);
123
124 /*
125 * get size of the entire block (overhead and all)
126 */
127 blk = BLOCK(p); /* back up to get length word */
128 blksize = SIZE(blk);
129 CLRBITS01(blksize);
130
131 /*
132 * locate the proper alignment boundary within the block.
133 */
134 x = (size_t)p;
135 if (x % align != 0)
136 x += align - (x % align);
137 alignedp = (TREE *)x;
138 aligned_blk = BLOCK(alignedp);
139
140 /*
141 * Check out the space to the left of the alignment
142 * boundary, and split off a fragment if necessary.
143 */
144 frag_size = (size_t)aligned_blk - (size_t)blk;
145 if (frag_size != 0) {
146 /*
147 * Create a fragment to the left of the aligned block.
148 */
149 if (frag_size < MINSIZE + WORDSIZE) {
150 /*
151 * Not enough space. So make the split
152 * at the other end of the alignment unit.
153 * We know this yields enough space, because
154 * we forced align >= MINSIZE + WORDSIZE above.
155 */
156 frag_size += align;
157 aligned_blk = _nextblk(aligned_blk, align);
158 }
159 blksize -= frag_size;
160 SIZE(aligned_blk) = blksize | BIT0;
161 frag_size -= WORDSIZE;
162 SIZE(blk) = frag_size | BIT0 | ISBIT1(SIZE(blk));
163 _free_unlocked(DATA(blk));
164 }
165
166 /*
167 * Is there a (sufficiently large) fragment to the
168 * right of the aligned block?
169 */
170 frag_size = blksize - nbytes;
171 if (frag_size >= MINSIZE + WORDSIZE) {
172 /*
173 * split and free a fragment on the right
174 */
175 blksize = SIZE(aligned_blk);
176 SIZE(aligned_blk) = nbytes;
177 blk = NEXT(aligned_blk);
178 SETOLD01(SIZE(aligned_blk), blksize);
179 frag_size -= WORDSIZE;
180 SIZE(blk) = frag_size | BIT0;
181 _free_unlocked(DATA(blk));
182 }
183 (void) mutex_unlock(&libc_malloc_lock);
184 return (DATA(aligned_blk));
185 }
186