malloc/alloc_buffer_alloc_array.c

   1 /* Array allocation from a fixed-size buffer.
   2    Copyright (C) 2017-2022 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 <alloc_buffer.h>
  20 #include <libc-pointer-arith.h>
  21
  22 void *
  23 __libc_alloc_buffer_alloc_array (struct alloc_buffer *buf, size_t element_size,
  24                                  size_t align, size_t count)
  25 {
  26   uintptr_t current = buf->__alloc_buffer_current;
  27   /* The caller asserts that align is a power of two.  */
  28   uintptr_t aligned = ALIGN_UP (current, align);
  29   size_t size;
  30   bool overflow = __builtin_mul_overflow (element_size, count, &size);
  31   uintptr_t new_current = aligned + size;
  32   if (!overflow                /* Multiplication did not overflow.  */
  33       && aligned >= current    /* No overflow in align step.  */
  34       && new_current >= size   /* No overflow in size computation.  */
  35       && new_current <= buf->__alloc_buffer_end) /* Room in buffer.  */
  36     {
  37       buf->__alloc_buffer_current = new_current;
  38       return (void *) aligned;
  39     }
  40   else
  41     {
  42       alloc_buffer_mark_failed (buf);
  43       return NULL;
  44     }
  45 }
  46 libc_hidden_def (__libc_alloc_buffer_alloc_array)