Documentation/vDSO/vdso_test.c

   1 /*
   2  * vdso_test.c: Sample code to test parse_vdso.c
   3  * Copyright (c) 2014 Andy Lutomirski
   4  * Subject to the GNU General Public License, version 2
   5  *
   6  * Compile with:
   7  * gcc -std=gnu99 vdso_test.c parse_vdso.c
   8  *
   9  * Tested on x86, 32-bit and 64-bit.  It may work on other architectures, too.
  10  */
  11
  12 #include <stdint.h>
  13 #include <elf.h>
  14 #include <stdio.h>
  15 #include <sys/auxv.h>
  16 #include <sys/time.h>
  17
  18 extern void *vdso_sym(const char *version, const char *name);
  19 extern void vdso_init_from_sysinfo_ehdr(uintptr_t base);
  20 extern void vdso_init_from_auxv(void *auxv);
  21
  22 int main(int argc, char **argv)
  23 {
  24         unsigned long sysinfo_ehdr = getauxval(AT_SYSINFO_EHDR);
  25         if (!sysinfo_ehdr) {
  26                 printf("AT_SYSINFO_EHDR is not present!\n");
  27                 return 0;
  28         }
  29
  30         vdso_init_from_sysinfo_ehdr(getauxval(AT_SYSINFO_EHDR));
  31
  32         /* Find gettimeofday. */
  33         typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz);
  34         gtod_t gtod = (gtod_t)vdso_sym("LINUX_2.6", "__vdso_gettimeofday");
  35
  36         if (!gtod) {
  37                 printf("Could not find __vdso_gettimeofday\n");
  38                 return 1;
  39         }
  40
  41         struct timeval tv;
  42         long ret = gtod(&tv, 0);
  43
  44         if (ret == 0) {
  45                 printf("The time is %lld.%06lld\n",
  46                        (long long)tv.tv_sec, (long long)tv.tv_usec);
  47         } else {
  48                 printf("__vdso_gettimeofday failed\n");
  49         }
  50
  51         return 0;
  52 }