glibc/debug/strcat_chk.c

/* Copyright (C) 1991-2023 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <string.h>
#include <memcopy.h>


/* Append SRC on the end of DEST.  */
char *
__strcat_chk (char *dest, const char *src, size_t destlen)
{
  char *s1 = dest;
  const char *s2 = src;
  char c;

  /* Find the end of the string.  */
  do
    {
      if (__glibc_unlikely (destlen-- == 0))
	__chk_fail ();
      c = *s1++;
    }
  while (c != '\0');

  /* Make S1 point before the next character, so we can increment
     it while memory is read (wins on pipelined cpus).  */
  ++destlen;
  s1 -= 2;

  do
    {
      if (__glibc_unlikely (destlen-- == 0))
	__chk_fail ();
      c = *s2++;
      *++s1 = c;
    }
  while (c != '\0');

  return dest;
}