#include <stdio.h>
#include <signal.h>
#include <asm/ldt.h>
#include <asm/segment.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/mman.h>
#define __KERNEL__
#include <asm/page.h>

extern void sysenter_call(pid_t pid, int signo, short ds, void *addr);
extern void sysenter_call_2(pid_t pid, int signo, void *addr);
void catch_sig(int signo, struct sigcontext ctx)
{
	__asm__ __volatile__("mov %0, %%ds" : : "r" (__USER_DS));
	printf("interrupted %%ebp = 0x%x\n", ctx.ebp);
	if (ctx.ebp == 0xbaadf00d)
		printf("phew\n");
}

void main(void)
{
	struct user_desc desc;
	short ds;
	unsigned long addr;
	unsigned *stack;
	unsigned long offset;

	stack = (unsigned *)mmap(0, 4096, PROT_EXEC|PROT_READ|PROT_WRITE,
				 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
	stack = &stack[1024];
	addr = 0xf0000;
	offset = __PAGE_OFFSET-(unsigned)stack+addr+16;
	signal(SIGUSR1, catch_sig);
	desc.entry_number = 0;
	desc.base_addr = offset;
	desc.limit = 0xffffff;
	desc.seg_32bit = 1;
	desc.contents = MODIFY_LDT_CONTENTS_DATA;
	desc.read_exec_only = 0;
	desc.limit_in_pages = 1;
	desc.seg_not_present = 0;
	desc.useable = 1;
	if (modify_ldt(1, &desc, sizeof(desc)) != 0) {
		perror("modify_ldt");
	}
	ds = 0x7; /* TI | RPL 3 */
	sysenter_call(getpid(), SIGUSR1, ds, stack);
	sysenter_call_2(getpid(), SIGSTOP, __PAGE_OFFSET+4096);
	printf("not reached - core should show %%eax == -EFAULT\n");
}