#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <linux/unistd.h>
#include <asm/ldt.h>
#include <asm/segment.h>
#include <asm/page.h>
#include <sys/mman.h>

_syscall3(int, modify_ldt, int, func, void *, ptr, unsigned long, bytecount)

static int set_ldt_entry(int entry, unsigned long base, unsigned int limit,
	      int seg_32bit_flag, int contents, int read_only_flag,
	      int limit_in_pages_flag, int seg_not_present, int useable)
{
  struct modify_ldt_ldt_s ldt_info;
  ldt_info.entry_number = entry;
  ldt_info.base_addr = base;
  ldt_info.limit = limit;
  ldt_info.seg_32bit = seg_32bit_flag;
  ldt_info.contents = contents;
  ldt_info.read_exec_only = read_only_flag;
  ldt_info.limit_in_pages = limit_in_pages_flag;
  ldt_info.seg_not_present = seg_not_present;
  ldt_info.useable = useable;

  return modify_ldt(1, &ldt_info, sizeof(ldt_info));
}

void my_trap(int sig)
{
  printf("Test passed, All OK!\n");
  exit(0);
}

int main(int argc, char *argv[])
{
  unsigned char *ptr;
  if (mmap(0, PAGE_SIZE, PROT_READ | PROT_WRITE,
      MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0) == MAP_FAILED) {
    perror("mmap");
    return 1;
  }
  if ((ptr = mmap(0, PAGE_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC,
      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0)) == MAP_FAILED) {
    perror("mmap");
    return 1;
  }
  if (argc == 1)		/* no-Oops mode */
    *(unsigned char *)0 = 1;	/* Set the no-Oops flag :) */
  /* Create the LDT entry */
  #define MY_CS (__USER_CS | 4)
  set_ldt_entry(MY_CS >> 3, (unsigned long)ptr, PAGE_SIZE - 1, 1,
    MODIFY_LDT_CONTENTS_CODE, 1, 0, 0, 0);
  ptr[0] = 0xcc;
  ptr[1] = 0xcb;
  signal(SIGTRAP, my_trap);
  asm volatile ("lcall %0,$0\n"::"i"(MY_CS));
  printf("Stolen interrupt, very bad.\n");
  return 0;
}