1  /* Copyright (C) 2008-2023 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 <errno.h>
      19  #include <sys/times.h>
      20  #include <sysdep.h>
      21  
      22  
      23  clock_t
      24  __times (struct tms *buf)
      25  {
      26    clock_t ret = INTERNAL_SYSCALL_CALL (times, buf);
      27    if (INTERNAL_SYSCALL_ERROR_P (ret)
      28        && __glibc_unlikely (INTERNAL_SYSCALL_ERRNO (ret) == EFAULT)
      29        && buf)
      30      {
      31        /* This might be an error or not.  For architectures which have no
      32  	 separate return value and error indicators we cannot
      33  	 distinguish a return value of e.g. (clock_t) -14 from -EFAULT.
      34  	 Therefore the only course of action is to dereference the user
      35  	 -supplied structure on a return of (clock_t) -14.  This will crash
      36  	 applications which pass in an invalid non-NULL BUF pointer.
      37  	 Note that Linux allows BUF to be NULL in which case we skip this.  */
      38  #define touch(v) \
      39        do {								      \
      40  	clock_t temp = v;						      \
      41  	asm volatile ("" : "+r" (temp));				      \
      42  	v = temp;							      \
      43        } while (0)
      44        touch (buf->tms_utime);
      45        touch (buf->tms_stime);
      46        touch (buf->tms_cutime);
      47        touch (buf->tms_cstime);
      48  
      49        /* If we come here the memory is valid and the kernel did not
      50  	 return an EFAULT error, but rather e.g. (clock_t) -14.
      51  	 Return the value given by the kernel.  */
      52      }
      53  
      54    /* On Linux this function never fails except with EFAULT.
      55       POSIX says that returning a value (clock_t) -1 indicates an error,
      56       but on Linux this is simply one of the valid clock values after
      57       clock_t wraps.  Therefore when we would return (clock_t) -1, we
      58       instead return (clock_t) 0, and loose a tick of accuracy (having
      59       returned 0 for two consecutive calls even though the clock
      60       advanced).  */
      61    if (ret == (clock_t) -1)
      62      return (clock_t) 0;
      63  
      64    return ret;
      65  }
      66  weak_alias (__times, times)