debug/strncat_chk.c

   1 /* Copyright (C) 1991-2023 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <string.h>
  19
  20 #include <memcopy.h>
  21
  22
  23 char *
  24 __strncat_chk (char *s1, const char *s2, size_t n, size_t s1len)
  25 {
  26   char c;
  27   char *s = s1;
  28
  29   /* Find the end of S1.  */
  30   do
  31     {
  32       if (__glibc_unlikely (s1len-- == 0))
  33         __chk_fail ();
  34       c = *s1++;
  35     }
  36   while (c != '\0');
  37
  38   /* Make S1 point before next character, so we can increment
  39      it while memory is read (wins on pipelined cpus).  */
  40   ++s1len;
  41   s1 -= 2;
  42
  43   if (n >= 4)
  44     {
  45       size_t n4 = n >> 2;
  46       do
  47         {
  48           if (__glibc_unlikely (s1len-- == 0))
  49             __chk_fail ();
  50           c = *s2++;
  51           *++s1 = c;
  52           if (c == '\0')
  53             return s;
  54           if (__glibc_unlikely (s1len-- == 0))
  55             __chk_fail ();
  56           c = *s2++;
  57           *++s1 = c;
  58           if (c == '\0')
  59             return s;
  60           if (__glibc_unlikely (s1len-- == 0))
  61             __chk_fail ();
  62           c = *s2++;
  63           *++s1 = c;
  64           if (c == '\0')
  65             return s;
  66           if (__glibc_unlikely (s1len-- == 0))
  67             __chk_fail ();
  68           c = *s2++;
  69           *++s1 = c;
  70           if (c == '\0')
  71             return s;
  72         } while (--n4 > 0);
  73       n &= 3;
  74     }
  75
  76   while (n > 0)
  77     {
  78       if (__glibc_unlikely (s1len-- == 0))
  79         __chk_fail ();
  80       c = *s2++;
  81       *++s1 = c;
  82       if (c == '\0')
  83         return s;
  84       n--;
  85     }
  86
  87   if (c != '\0')
  88     {
  89       if (__glibc_unlikely (s1len-- == 0))
  90         __chk_fail ();
  91       *++s1 = '\0';
  92     }
  93
  94   return s;
  95 }