malloc/scratch_buffer_grow_preserve.c

   1 /* Variable-sized buffer with on-stack default allocation.
   2    Copyright (C) 2015 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    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <scratch_buffer.h>
  20 #include <errno.h>
  21 #include <string.h>
  22
  23 bool
  24 __libc_scratch_buffer_grow_preserve (struct scratch_buffer *buffer)
  25 {
  26   size_t new_length = 2 * buffer->length;
  27   void *new_ptr;
  28
  29   if (buffer->data == buffer->__space)
  30     {
  31       /* Move buffer to the heap.  No overflow is possible because
  32          buffer->length describes a small buffer on the stack.  */
  33       new_ptr = malloc (new_length);
  34       if (new_ptr == NULL)
  35         return false;
  36       memcpy (new_ptr, buffer->__space, buffer->length);
  37     }
  38   else
  39     {
  40       /* Buffer was already on the heap.  Check for overflow.  */
  41       if (__glibc_likely (new_length >= buffer->length))
  42         new_ptr = realloc (buffer->data, new_length);
  43       else
  44         {
  45           __set_errno (ENOMEM);
  46           new_ptr = NULL;
  47         }
  48
  49       if (__glibc_unlikely (new_ptr == NULL))
  50         {
  51           /* Deallocate, but buffer must remain valid to free.  */
  52           free (buffer->data);
  53           scratch_buffer_init (buffer);
  54           return false;
  55         }
  56     }
  57
  58   /* Install new heap-based buffer.  */
  59   buffer->data = new_ptr;
  60   buffer->length = new_length;
  61   return true;
  62 }
  63 libc_hidden_def (__libc_scratch_buffer_grow_preserve);