vvar.c

#include <stdint.h>
#include <stdio.h>
#include <sys/auxv.h>

int main(int argc, char** argv, char** envv) {
  uintptr_t vdso_base = getauxval(AT_SYSINFO_EHDR);
  vdso_base &= ~0xfff; // round down;
  printf("VDSO base: %#llx\n", vdso_base);

  // Linux 5.6+ have 4 pages of VVAR.
  uintptr_t vvar_offset = 4 * 4096;
  // Linux 4.12+ have 3 pages of VVAR.
  //vvar_offset = 3 * 4096;
  // Linux 4.7+ have 2 pages of VVAR.
  //vvar_offset = 2 * 4096;
  // Earlier has 1 page.
  //vvar_offset = 1 * 4096;

  uintptr_t vvar_base = vdso_base - vvar_offset;

  // Dump first 512 bytes.
  for (int i = 0; i < 512; i += 4) {
    uintptr_t addr = vvar_base + i;
    if (i % 16 == 0) {
      printf("\n%#llx:", addr);
    }
    printf(" 0x%08x", *(uint32_t*)addr);
  }

  return 0;
}