usr/src/lib/libc/port/gen/memalign.c

   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  * Copyright 2016 Joyent, Inc.
  26  */
  27
  28 /*      Copyright (c) 1988 AT&T */
  29 /*        All Rights Reserved   */
  30
  31 #include "lint.h"
  32 #include "mallint.h"
  33 #include "mtlib.h"
  34
  35 #define _misaligned(p)          ((unsigned)(p) & 3)
  36                 /* 4-byte "word" alignment is considered ok in LP64 */
  37 #define _nextblk(p, size)       ((TREE *)((uintptr_t)(p) + (size)))
  38
  39 /*
  40  * memalign(align, nbytes)
  41  *
  42  * Description:
  43  *      Returns a block of specified size on a specified alignment boundary.
  44  *
  45  * Algorithm:
  46  *      Malloc enough to ensure that a block can be aligned correctly.
  47  *      Find the alignment point and return the fragments
  48  *      before and after the block.
  49  *
  50  * Errors:
  51  *      Returns NULL and sets errno as follows:
  52  *      [EINVAL]
  53  *              if nbytes = 0,
  54  *              or if alignment is misaligned,
  55  *              or if the heap has been detectably corrupted.
  56  *      [ENOMEM]
  57  *              if the requested memory could not be allocated.
  58  */
  59
  60 void *
  61 memalign(size_t align, size_t nbytes)
  62 {
  63         size_t   reqsize;       /* Num of bytes to get from malloc() */
  64         TREE    *p;             /* Ptr returned from malloc() */
  65         TREE    *blk;           /* For addressing fragment blocks */
  66         size_t  blksize;        /* Current (shrinking) block size */
  67         TREE    *alignedp;      /* Ptr to properly aligned boundary */
  68         TREE    *aligned_blk;   /* The block to be returned */
  69         size_t  frag_size;      /* size of fragments fore and aft */
  70         size_t   x;
  71
  72         if (!primary_link_map) {
  73                 errno = ENOTSUP;
  74                 return (NULL);
  75         }
  76
  77         /*
  78          * check for valid size and alignment parameters
  79          * MAX_ALIGN check prevents overflow in later calculation.
  80          */
  81         if (nbytes == 0 || _misaligned(align) || align == 0 ||
  82             align > MAX_ALIGN) {
  83                 errno = EINVAL;
  84                 return (NULL);
  85         }
  86
  87         /*
  88          * Malloc enough memory to guarantee that the result can be
  89          * aligned correctly. The worst case is when malloc returns
  90          * a block so close to the next alignment boundary that a
  91          * fragment of minimum size cannot be created.  In order to
  92          * make sure we can handle this, we need to force the
  93          * alignment to be at least as large as the minimum frag size
  94          * (MINSIZE + WORDSIZE).
  95          */
  96
  97         /* check for size that could overflow calculations */
  98         if (nbytes > MAX_MALLOC) {
  99                 errno = ENOMEM;
 100                 return (NULL);
 101         }
 102         ROUND(nbytes);
 103         if (nbytes < MINSIZE)
 104                 nbytes = MINSIZE;
 105         ROUND(align);
 106         while (align < MINSIZE + WORDSIZE)
 107                 align <<= 1;
 108         reqsize = nbytes + align + (MINSIZE + WORDSIZE);
 109
 110         /* check for overflow */
 111         if (reqsize < nbytes) {
 112                 errno = ENOMEM;
 113                 return (NULL);
 114         }
 115
 116         p = (TREE *)malloc(reqsize);
 117         if (p == (TREE *)NULL) {
 118                 /* malloc sets errno */
 119                 return (NULL);
 120         }
 121         (void) mutex_lock(&libc_malloc_lock);
 122
 123         /*
 124          * get size of the entire block (overhead and all)
 125          */
 126         blk = BLOCK(p);                 /* back up to get length word */
 127         blksize = SIZE(blk);
 128         CLRBITS01(blksize);
 129
 130         /*
 131          * locate the proper alignment boundary within the block.
 132          */
 133         x = (size_t)p;
 134         if (x % align != 0)
 135                 x += align - (x % align);
 136         alignedp = (TREE *)x;
 137         aligned_blk = BLOCK(alignedp);
 138
 139         /*
 140          * Check out the space to the left of the alignment
 141          * boundary, and split off a fragment if necessary.
 142          */
 143         frag_size = (size_t)aligned_blk - (size_t)blk;
 144         if (frag_size != 0) {
 145                 /*
 146                  * Create a fragment to the left of the aligned block.
 147                  */
 148                 if (frag_size < MINSIZE + WORDSIZE) {
 149                         /*
 150                          * Not enough space. So make the split
 151                          * at the other end of the alignment unit.
 152                          * We know this yields enough space, because
 153                          * we forced align >= MINSIZE + WORDSIZE above.
 154                          */
 155                         frag_size += align;
 156                         aligned_blk = _nextblk(aligned_blk, align);
 157                 }
 158                 blksize -= frag_size;
 159                 SIZE(aligned_blk) = blksize | BIT0;
 160                 frag_size -= WORDSIZE;
 161                 SIZE(blk) = frag_size | BIT0 | ISBIT1(SIZE(blk));
 162                 _free_unlocked(DATA(blk));
 163         }
 164
 165         /*
 166          * Is there a (sufficiently large) fragment to the
 167          * right of the aligned block?
 168          */
 169         frag_size = blksize - nbytes;
 170         if (frag_size >= MINSIZE + WORDSIZE) {
 171                 /*
 172                  * split and free a fragment on the right
 173                  */
 174                 blksize = SIZE(aligned_blk);
 175                 SIZE(aligned_blk) = nbytes;
 176                 blk = NEXT(aligned_blk);
 177                 SETOLD01(SIZE(aligned_blk), blksize);
 178                 frag_size -= WORDSIZE;
 179                 SIZE(blk) = frag_size | BIT0;
 180                 _free_unlocked(DATA(blk));
 181         }
 182         (void) mutex_unlock(&libc_malloc_lock);
 183         return (DATA(aligned_blk));
 184 }
 185
 186 /*
 187  * This is the ISO/IEC C11 version of memalign. We have kept it as a separate
 188  * function, but it is basically the same thing. Note that this is implemented
 189  * this way to make life easier to libraries which already interpose on
 190  * memalign.
 191  */
 192 void *
 193 aligned_alloc(size_t align, size_t size)
 194 {
 195         return (memalign(align, size));
 196 }