A simple program to verify si_code=128 behaviour .

trapex.c

/* Simple test program to verify si_code=SI_KERNEL(128) for address 
 * above TASK_SIZE64 or TASK_SIZE_MAX (0x800000000000 - 4096 = 0x7ffffffff000)
 * See do_page_fault(k).
 */
#include <stdio.h>
#include <sys/types.h>
#include <signal.h>
#include <string.h>
#include <unistd.h>

void action(int signo, siginfo_t *info, void *vc)
{
  printf("action sig=%d info {errno %d code %d addr %#lx} vc %#lx\n",
	 signo,
	 info->si_errno, info->si_code, info->si_addr,
	 vc);
  exit(1);
}

void setupHandler()
{
  int r;
  struct sigaction act;
  memset(&act, 0, sizeof(act));
  act.sa_sigaction = action;
  act.sa_flags = SA_SIGINFO;
  r = sigaction(SIGSEGV, &act, NULL);
}

int accessMem(long addr)
{
  char *cp = (char*)addr;
  return *cp;
}

int main(int argc, char *argv[])
{ 
  int r = -1;
  long l;
  /* l = 0x12345678aabbccddL; */
  l = 0x7fffffffff002;
  /* long l = 0xaabbccddL; */
  setupHandler();
  r = accessMem(l);
  return r;
}