lib/pagealign_alloc.c

   1 /* Memory allocation aligned to system page boundaries.
   2
   3    Copyright (C) 2005-2007, 2009-2021 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* Written by Derek R. Price <derek@ximbiot.com>.  */
  19
  20 #include <config.h>
  21
  22 #include "pagealign_alloc.h"
  23
  24 #include <errno.h>
  25 #include <stdlib.h>
  26
  27 #include <fcntl.h>
  28 #include <unistd.h>
  29
  30 #if HAVE_MMAP
  31 # include <sys/mman.h>
  32 #endif
  33
  34 #include "error.h"
  35 #include "xalloc.h"
  36 #include "gettext.h"
  37
  38 #define _(str) gettext (str)
  39
  40 #if HAVE_MMAP
  41 /* Define MAP_FILE when it isn't otherwise.  */
  42 # ifndef MAP_FILE
  43 #  define MAP_FILE 0
  44 # endif
  45 /* Define MAP_FAILED for old systems which neglect to.  */
  46 # ifndef MAP_FAILED
  47 #  define MAP_FAILED ((void *)-1)
  48 # endif
  49 #endif
  50
  51
  52 #if HAVE_MMAP || ! HAVE_POSIX_MEMALIGN
  53
  54 # if HAVE_MMAP
  55 /* For each memory region, we store its size.  */
  56 typedef size_t info_t;
  57 # else
  58 /* For each memory region, we store the original pointer returned by
  59    malloc().  */
  60 typedef void * info_t;
  61 # endif
  62
  63 /* A simple linked list of allocated memory regions.  It is probably not the
  64    most efficient way to store these, but anyway...  */
  65 typedef struct memnode_s memnode_t;
  66 struct memnode_s
  67 {
  68   void *aligned_ptr;
  69   info_t info;
  70   memnode_t *next;
  71 };
  72
  73 /* The list of currently allocated memory regions.  */
  74 static memnode_t *memnode_table = NULL;
  75
  76
  77 static void
  78 new_memnode (void *aligned_ptr, info_t info)
  79 {
  80   memnode_t *new_node = XMALLOC (memnode_t);
  81   new_node->aligned_ptr = aligned_ptr;
  82   new_node->info = info;
  83   new_node->next = memnode_table;
  84   memnode_table = new_node;
  85 }
  86
  87
  88 /* Dispose of the memnode containing a map for the ALIGNED_PTR in question
  89    and return the content of the node's INFO field.  */
  90 static info_t
  91 get_memnode (void *aligned_ptr)
  92 {
  93   info_t ret;
  94   memnode_t *c;
  95   memnode_t **p_next = &memnode_table;
  96
  97   for (c = *p_next; c != NULL; p_next = &c->next, c = c->next)
  98     if (c->aligned_ptr == aligned_ptr)
  99       break;
 100
 101   if (c == NULL)
 102     /* An attempt to free untracked memory.  A wrong pointer was passed
 103        to pagealign_free().  */
 104     abort ();
 105
 106   /* Remove this entry from the list, save the return value, and free it.  */
 107   *p_next = c->next;
 108   ret = c->info;
 109   free (c);
 110
 111   return ret;
 112 }
 113
 114 #endif /* HAVE_MMAP || !HAVE_POSIX_MEMALIGN */
 115
 116
 117 void *
 118 pagealign_alloc (size_t size)
 119 {
 120   void *ret;
 121   /* We prefer the mmap() approach over the posix_memalign() or malloc()
 122      based approaches, since the latter often waste an entire memory page
 123      per call.  */
 124 #if HAVE_MMAP
 125 # ifdef HAVE_MAP_ANONYMOUS
 126   const int fd = -1;
 127   const int flags = MAP_ANONYMOUS | MAP_PRIVATE;
 128 # else /* !HAVE_MAP_ANONYMOUS */
 129   static int fd = -1;  /* Only open /dev/zero once in order to avoid limiting
 130                           the amount of memory we may allocate based on the
 131                           number of open file descriptors.  */
 132   const int flags = MAP_FILE | MAP_PRIVATE;
 133   if (fd == -1)
 134     {
 135       fd = open ("/dev/zero", O_RDONLY | O_CLOEXEC, 0666);
 136       if (fd < 0)
 137         error (EXIT_FAILURE, errno, _("Failed to open /dev/zero for read"));
 138     }
 139 # endif /* HAVE_MAP_ANONYMOUS */
 140   ret = mmap (NULL, size, PROT_READ | PROT_WRITE, flags, fd, 0);
 141   if (ret == MAP_FAILED)
 142     return NULL;
 143   new_memnode (ret, size);
 144 #elif HAVE_POSIX_MEMALIGN
 145   int status = posix_memalign (&ret, getpagesize (), size);
 146   if (status)
 147     {
 148       errno = status;
 149       return NULL;
 150     }
 151 #else /* !HAVE_MMAP && !HAVE_POSIX_MEMALIGN */
 152   size_t pagesize = getpagesize ();
 153   void *unaligned_ptr = malloc (size + pagesize - 1);
 154   if (unaligned_ptr == NULL)
 155     {
 156       /* Set errno.  We don't know whether malloc already set errno: some
 157          implementations of malloc do, some don't.  */
 158       errno = ENOMEM;
 159       return NULL;
 160     }
 161   ret = (char *) unaligned_ptr
 162         + ((- (unsigned long) unaligned_ptr) & (pagesize - 1));
 163   new_memnode (ret, unaligned_ptr);
 164 #endif /* HAVE_MMAP && HAVE_POSIX_MEMALIGN */
 165   return ret;
 166 }
 167
 168
 169 void *
 170 pagealign_xalloc (size_t size)
 171 {
 172   void *ret;
 173
 174   ret = pagealign_alloc (size);
 175   if (ret == NULL)
 176     xalloc_die ();
 177   return ret;
 178 }
 179
 180
 181 void
 182 pagealign_free (void *aligned_ptr)
 183 {
 184 #if HAVE_MMAP
 185   if (munmap (aligned_ptr, get_memnode (aligned_ptr)) < 0)
 186     error (EXIT_FAILURE, errno, "Failed to unmap memory");
 187 #elif HAVE_POSIX_MEMALIGN
 188   free (aligned_ptr);
 189 #else
 190   free (get_memnode (aligned_ptr));
 191 #endif
 192 }