diff --git a/src/arch/x86_64/gdt.rs b/src/arch/x86_64/gdt.rs
index a4cee8f..2db9cca 100644
--- a/src/arch/x86_64/gdt.rs
+++ b/src/arch/x86_64/gdt.rs
@@ -32,8 +32,7 @@ pub fn init() {
     let mut tss_selector = SegmentSelector(0);
     let gdt = Box::new({
         let mut gdt = Gdt::new();
-        gdt.add_entry(GNULL);
-        code_selector = 
+        code_selector =
         gdt.add_entry(KCODE);
         gdt.add_entry(UCODE);
         gdt.add_entry(KDATA);
@@ -55,7 +54,6 @@ pub fn init() {
 pub const DOUBLE_FAULT_IST_INDEX: usize = 0;
 
 // Copied from xv6 x86_64
-const GNULL: Descriptor = Descriptor::UserSegment(0);
 const KCODE: Descriptor = Descriptor::UserSegment(0x0020980000000000);  // EXECUTABLE | USER_SEGMENT | PRESENT | LONG_MODE
 const UCODE: Descriptor = Descriptor::UserSegment(0x0020F80000000000);  // EXECUTABLE | USER_SEGMENT | USER_MODE | PRESENT | LONG_MODE
 const KDATA: Descriptor = Descriptor::UserSegment(0x0000920000000000);  // DATA_WRITABLE | USER_SEGMENT | PRESENT
diff --git a/src/arch/x86_64/idt.rs b/src/arch/x86_64/idt.rs
index e2d412b..f08428a 100644
--- a/src/arch/x86_64/idt.rs
+++ b/src/arch/x86_64/idt.rs
@@ -12,10 +12,14 @@ pub fn init() {
         let mut idt = Idt::new();
         idt.breakpoint.set_handler_fn(breakpoint_handler);
         idt.double_fault.set_handler_fn(double_fault_handler);
+        idt.general_protection_fault.set_handler_fn(general_protection_fault_handler);
         idt[(T_IRQ0 + IRQ_COM1) as usize].set_handler_fn(com1_handler);
         idt[(T_IRQ0 + IRQ_COM2) as usize].set_handler_fn(com2_handler);
         idt[(T_IRQ0 + IRQ_KBD) as usize].set_handler_fn(keyboard_handler);
         idt[(T_IRQ0 + IRQ_TIMER) as usize].set_handler_fn(timer_handler);
+        idt[T_SWITCH_TOU as usize].set_handler_fn(to_user_handler);
+        idt[T_SWITCH_TOK as usize].set_handler_fn(to_kernel_handler);
+        idt[T_SYSCALL as usize].set_handler_fn(syscall_handler);
         unsafe {
             idt.page_fault.set_handler_fn(page_fault_handler)
                 .set_stack_index(DOUBLE_FAULT_IST_INDEX as u16);
diff --git a/src/arch/x86_64/interrupt/irq.rs b/src/arch/x86_64/interrupt/irq.rs
index 1b5523b..b875805 100644
--- a/src/arch/x86_64/interrupt/irq.rs
+++ b/src/arch/x86_64/interrupt/irq.rs
@@ -22,6 +22,12 @@ pub extern "x86-interrupt" fn page_fault_handler(
     loop {}
 }
 
+pub extern "x86-interrupt" fn general_protection_fault_handler(
+    stack_frame: &mut ExceptionStackFrame, error_code: u64)
+{
+    println!("\nEXCEPTION: General Protection Fault\n{:#?}\nErrorCode: {:#x}", stack_frame, error_code);
+}
+
 #[cfg(feature = "use_apic")]
 use arch::driver::apic::ack;
 #[cfg(not(feature = "use_apic"))]
@@ -70,4 +76,26 @@ pub extern "x86-interrupt" fn timer_handler(
         println!("\nInterupt: Timer\ntick = {}", tick);
     }
     ack(IRQ_TIMER);    
+}
+
+pub extern "x86-interrupt" fn to_user_handler(
+    stack_frame: &mut ExceptionStackFrame)
+{
+    println!("\nInterupt: To User");
+    stack_frame.code_segment = 16;
+    stack_frame.stack_segment = 32;
+}
+
+pub extern "x86-interrupt" fn to_kernel_handler(
+    stack_frame: &mut ExceptionStackFrame)
+{
+    println!("\nInterupt: To Kernel");
+    stack_frame.code_segment = 8;
+    stack_frame.stack_segment = 24;
+}
+
+pub extern "x86-interrupt" fn syscall_handler(
+    stack_frame: &mut ExceptionStackFrame)
+{
+    println!("\nInterupt: Syscall");
 }
\ No newline at end of file
diff --git a/src/consts.rs b/src/consts.rs
index 67ab9b6..19f5cb3 100644
--- a/src/consts.rs
+++ b/src/consts.rs
@@ -104,4 +104,7 @@ pub mod irq {
 	pub const IRQ_IDE      : u8 = 14;
 	pub const IRQ_ERROR    : u8 = 19;
 	pub const IRQ_SPURIOUS : u8 = 31;
+    pub const T_SYSCALL    : u8 = 0x80;     // SYSCALL, ONLY FOR THIS PROJ
+    pub const T_SWITCH_TOU : u8 = 120;      // user/kernel switch
+    pub const T_SWITCH_TOK : u8 = 121;      // user/kernel switch
 }
diff --git a/src/lib.rs b/src/lib.rs
index 3affcd9..fc4f920 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -9,6 +9,7 @@
 #![feature(abi_x86_interrupt)]
 #![feature(iterator_step_by)]
 #![feature(unboxed_closures)]
+#![feature(asm)]
 #![no_std]
 
 
@@ -21,6 +22,7 @@ extern crate spin;
 extern crate multiboot2;
 #[macro_use]
 extern crate bitflags;
+#[macro_use]
 extern crate x86_64;
 #[macro_use]
 extern crate once;
@@ -74,6 +76,9 @@ pub extern "C" fn rust_main(multiboot_information_address: usize) -> ! {
     arch::smp::start_other_cores(&acpi, &mut memory_controller);
 
     unsafe{ arch::interrupt::enable(); }
+
+    unsafe{ int!(120); } // to user
+
     loop{}
 
     test_end!();