support/support_shared_allocate.c

   1 /* Allocate a memory region shared across processes.
   2    Copyright (C) 2017-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library 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 GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include <stddef.h>
  21 #include <support/support.h>
  22 #include <support/xunistd.h>
  23 #include <sys/mman.h>
  24
  25 /* Header for the allocation.  It contains the size of the allocation
  26    for subsequent unmapping.  */
  27 struct header
  28 {
  29   size_t total_size;
  30   char data[] __attribute__ ((aligned (__alignof__ (max_align_t))));
  31 };
  32
  33 void *
  34 support_shared_allocate (size_t size)
  35 {
  36   size_t total_size = size + offsetof (struct header, data);
  37   if (total_size < size)
  38     {
  39       errno = ENOMEM;
  40       oom_error (__func__, size);
  41       return NULL;
  42     }
  43   else
  44     {
  45       struct header *result = xmmap (NULL, total_size, PROT_READ | PROT_WRITE,
  46                                      MAP_ANONYMOUS | MAP_SHARED, -1);
  47       result->total_size = total_size;
  48       return &result->data;
  49     }
  50 }
  51
  52 void
  53 support_shared_free (void *data)
  54 {
  55   struct header *header = data - offsetof (struct header, data);
  56   xmunmap (header, header->total_size);
  57 }