malloc/scratch_buffer_grow_preserve.c

   1 /* Variable-sized buffer with on-stack default allocation.
   2    Copyright (C) 2015-2024 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 #ifndef _LIBC
  20 # include <libc-config.h>
  21 #endif
  22
  23 #include <scratch_buffer.h>
  24 #include <errno.h>
  25 #include <string.h>
  26
  27 bool
  28 __libc_scratch_buffer_grow_preserve (struct scratch_buffer *buffer)
  29 {
  30   size_t new_length = 2 * buffer->length;
  31   void *new_ptr;
  32
  33   if (buffer->data == buffer->__space.__c)
  34     {
  35       /* Move buffer to the heap.  No overflow is possible because
  36          buffer->length describes a small buffer on the stack.  */
  37       new_ptr = malloc (new_length);
  38       if (new_ptr == NULL)
  39         return false;
  40       memcpy (new_ptr, buffer->__space.__c, buffer->length);
  41     }
  42   else
  43     {
  44       /* Buffer was already on the heap.  Check for overflow.  */
  45       if (__glibc_likely (new_length >= buffer->length))
  46         new_ptr = realloc (buffer->data, new_length);
  47       else
  48         {
  49           __set_errno (ENOMEM);
  50           new_ptr = NULL;
  51         }
  52
  53       if (__glibc_unlikely (new_ptr == NULL))
  54         {
  55           /* Deallocate, but buffer must remain valid to free.  */
  56           free (buffer->data);
  57           scratch_buffer_init (buffer);
  58           return false;
  59         }
  60     }
  61
  62   /* Install new heap-based buffer.  */
  63   buffer->data = new_ptr;
  64   buffer->length = new_length;
  65   return true;
  66 }
  67 libc_hidden_def (__libc_scratch_buffer_grow_preserve)