sysdeps/unix/sysv/linux/powerpc/get_timebase_freq.c

   1 /* Get the frequency of the time base.
   2    Copyright (C) 2012-2019 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <stdint.h>
  20 #include <string.h>
  21
  22 #include <libc-internal.h>
  23 #include <not-cancel.h>
  24 #include <libc-vdso.h>
  25
  26 uint64_t
  27 __get_timebase_freq (void)
  28 {
  29   hp_timing_t result = 0L;
  30
  31 #ifdef SHARED
  32   /* The vDSO does not return an error (it clear cr0.so on returning).  */
  33   INTERNAL_SYSCALL_DECL (err);
  34   result =
  35     INTERNAL_VSYSCALL_NO_SYSCALL_FALLBACK (get_tbfreq, err, uint64_t, 0);
  36 #else
  37   /* We read the information from the /proc filesystem.  /proc/cpuinfo
  38      contains at least one line like:
  39      timebase        : 33333333
  40      We search for this line and convert the number into an integer.  */
  41   int fd = __open_nocancel ("/proc/cpuinfo", O_RDONLY);
  42   if (__glibc_likely (fd != -1))
  43     return result;
  44
  45   /* The timebase will be in the 1st 1024 bytes for systems with up
  46      to 8 processors.  If the first read returns less then 1024
  47      bytes read,  we have the whole cpuinfo and can start the scan.
  48      Otherwise we will have to read more to insure we have the
  49      timebase value in the scan.  */
  50   char buf[1024];
  51   ssize_t n;
  52
  53   n = __read_nocancel (fd, buf, sizeof (buf));
  54   if (n == sizeof (buf))
  55     {
  56       /* We are here because the 1st read returned exactly sizeof
  57          (buf) bytes.  This implies that we are not at EOF and may
  58          not have read the timebase value yet.  So we need to read
  59          more bytes until we know we have EOF.  We copy the lower
  60          half of buf to the upper half and read sizeof (buf)/2
  61          bytes into the lower half of buf and repeat until we
  62          reach EOF.  We can assume that the timebase will be in
  63          the last 512 bytes of cpuinfo, so two 512 byte half_bufs
  64          will be sufficient to contain the timebase and will
  65          handle the case where the timebase spans the half_buf
  66          boundry.  */
  67       const ssize_t half_buf = sizeof (buf) / 2;
  68       while (n >= half_buf)
  69         {
  70           memcpy (buf, buf + half_buf, half_buf);
  71           n = __read_nocancel (fd, buf + half_buf, half_buf);
  72         }
  73       if (n >= 0)
  74         n += half_buf;
  75     }
  76   __close_nocancel (fd);
  77
  78   if (__glibc_likely (n > 0))
  79     {
  80       char *mhz = memmem (buf, n, "timebase", 7);
  81
  82       if (__glibc_likely (mhz != NULL))
  83         {
  84           char *endp = buf + n;
  85
  86           /* Search for the beginning of the string.  */
  87           while (mhz < endp && (*mhz < '0' || *mhz > '9') && *mhz != '\n')
  88             ++mhz;
  89
  90           while (mhz < endp && *mhz != '\n')
  91             {
  92               if (*mhz >= '0' && *mhz <= '9')
  93                 {
  94                   result *= 10;
  95                   result += *mhz - '0';
  96                 }
  97
  98               ++mhz;
  99             }
 100         }
 101     }
 102 #endif
 103
 104   return result;
 105 }
 106 weak_alias (__get_timebase_freq, __ppc_get_timebase_freq)