auxval.c

#include <sys/types.h>
#include <sys/auxv.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <assert.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

// for simplicity, no optimizations in mind..
static unsigned long proc_getauxval(unsigned long type) {
  unsigned long auxv[4096 / sizeof(unsigned long)] = {0,};

  int fd = open("/proc/self/auxv", O_RDONLY);
  assert(fd >= 0);

  long nb = read(fd, auxv, sizeof(auxv));
  assert(nb >= 0);
  close(fd);

  for (int i = 0; i < nb / sizeof(long); i+=2) {
    if (auxv[i] == type) {
      return auxv[i+1];
    }
  }

  return 0;
}

static struct auxval {
  unsigned long type;
  const char* desc;
} auxvals[] =
  {
   { AT_BASE, "AT_BASE", },
   { AT_ENTRY, "AT_ENTRY", },
   { AT_HWCAP, "AT_HWCAP", },
  };
  
int main(int argc, char** argv) {
  unsigned long vals[2];

  for (int i = 0; i < sizeof(auxvals) / sizeof(auxvals[0]); i++) {
    vals[0] = getauxval(auxvals[i].type);
    vals[1] = proc_getauxval(auxvals[i].type);
    printf("%16s: getauxval = 0x%-16lx, proc_getauxval = 0x%-16lx\n",
	   auxvals[i].desc, vals[0], vals[1]);
  }
  
  return 0;
}