gcc/libssp/strncat-chk.c

/* Checking strncat.
   Copyright (C) 1991, 1997, 2003, 2004, 2005 Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 2, or (at your option) any later
version.

In addition to the permissions in the GNU General Public License, the
Free Software Foundation gives you unlimited permission to link the
compiled version of this file into combinations with other programs,
and to distribute those combinations without any restriction coming
from the use of this file.  (The General Public License restrictions
do apply in other respects; for example, they cover modification of
the file, and distribution when not linked into a combine
executable.)

GCC 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 General Public License
for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING.  If not, write to the Free
Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301, USA.  */

/* As a special exception, if you link this library with files compiled with
   GCC to produce an executable, this does not cause the resulting executable
   to be covered by the GNU General Public License. This exception does not
   however invalidate any other reasons why the executable file might be
   covered by the GNU General Public License.  */

#include "config.h"
#include <ssp/ssp.h>
#ifdef HAVE_STRING_H
# include <string.h>
#endif

extern void __chk_fail (void) __attribute__((__noreturn__));

char *
__strncat_chk (char *__restrict__ dest, const char *__restrict__ src,
               size_t n, size_t slen)
{
  char c;
  char *s = dest;

  do
    {
      if (slen-- == 0)
        __chk_fail ();
      c = *dest++;
    }
  while (c != '\0');

  ++slen;
  dest -= 2;

  if (n >= 4)
    {
      size_t n4 = n >> 2;
      do
        {
          if (slen-- == 0)
            __chk_fail ();
          c = *src++;
          *++dest = c;
          if (c == '\0')
            return s;
          if (slen-- == 0)
            __chk_fail ();
          c = *src++;
          *++dest = c;
          if (c == '\0')
            return s;
          if (slen-- == 0)
            __chk_fail ();
          c = *src++;
          *++dest = c;
          if (c == '\0')
            return s;
          if (slen-- == 0)
            __chk_fail ();
          c = *src++;
          *++dest = c;
          if (c == '\0')
            return s;
          if (slen-- == 0)
            __chk_fail ();
          c = *src++;
          *++dest = c;
          if (c == '\0')
            return s;
        } while (--n4 > 0);
      n &= 3;
    }

  while (n > 0)
    {
      if (slen-- == 0)
        __chk_fail ();
      c = *src++;
      *++dest = c;
      if (c == '\0')
        return s;
      n--;
    }

  if (c != '\0')
    {
      if (slen-- == 0)
        __chk_fail ();
      *++dest = '\0';
    }

  return s;
}