sysdeps/unix/sysv/linux/times.c

   1 /* Copyright (C) 2008-2017 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    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <errno.h>
  19 #include <sys/times.h>
  20 #include <sysdep.h>
  21
  22
  23 clock_t
  24 __times (struct tms *buf)
  25 {
  26   INTERNAL_SYSCALL_DECL (err);
  27   clock_t ret = INTERNAL_SYSCALL (times, err, 1, buf);
  28   if (INTERNAL_SYSCALL_ERROR_P (ret, err)
  29       && __builtin_expect (INTERNAL_SYSCALL_ERRNO (ret, err) == EFAULT, 0)
  30       && buf)
  31     {
  32       /* This might be an error or not.  For architectures which have no
  33          separate return value and error indicators we cannot
  34          distinguish a return value of e.g. (clock_t) -14 from -EFAULT.
  35          Therefore the only course of action is to dereference the user
  36          -supplied structure on a return of (clock_t) -14.  This will crash
  37          applications which pass in an invalid non-NULL BUF pointer.
  38          Note that Linux allows BUF to be NULL in which case we skip this.  */
  39 #define touch(v) \
  40       do {                                                                    \
  41         clock_t temp = v;                                                     \
  42         asm volatile ("" : "+r" (temp));                                      \
  43         v = temp;                                                             \
  44       } while (0)
  45       touch (buf->tms_utime);
  46       touch (buf->tms_stime);
  47       touch (buf->tms_cutime);
  48       touch (buf->tms_cstime);
  49
  50       /* If we come here the memory is valid and the kernel did not
  51          return an EFAULT error, but rather e.g. (clock_t) -14.
  52          Return the value given by the kernel.  */
  53     }
  54
  55   /* On Linux this function never fails except with EFAULT.
  56      POSIX says that returning a value (clock_t) -1 indicates an error,
  57      but on Linux this is simply one of the valid clock values after
  58      clock_t wraps.  Therefore when we would return (clock_t) -1, we
  59      instead return (clock_t) 0, and loose a tick of accuracy (having
  60      returned 0 for two consecutive calls even though the clock
  61      advanced).  */
  62   if (ret == (clock_t) -1)
  63     return (clock_t) 0;
  64
  65   return ret;
  66 }
  67 weak_alias (__times, times)