diff --git a/src/interrupt/syscall.rs b/src/interrupt/syscall.rs
index d1527da..bc4ea43 100644
--- a/src/interrupt/syscall.rs
+++ b/src/interrupt/syscall.rs
@@ -1,23 +1,19 @@
 #[naked]
 pub unsafe extern fn syscall() {
     #[inline(never)]
-    unsafe fn inner() {
+    unsafe fn inner(stack: &mut SyscallStack) {
         extern {
-            fn syscall(a: usize, b: usize, c: usize, d: usize, e: usize, f: usize, stack: usize) -> usize;
+            fn syscall(a: usize, b: usize, c: usize, d: usize, e: usize, f: usize, rbp: usize, stack: &mut SyscallStack) -> usize;
         }
 
         let mut a;
         {
             let b;
-            let c;
-            let d;
-            let e;
-            let f;
-            let stack;
-            asm!("" : "={rax}"(a), "={rbx}"(b), "={rcx}"(c), "={rdx}"(d), "={rsi}"(e), "={rdi}"(f), "={rbp}"(stack)
+            let rbp;
+            asm!("" : "={rax}"(a), "={rbx}"(b), "={rbp}"(rbp)
                 : : : "intel", "volatile");
 
-            a = syscall(a, b, c, d, e, f, stack);
+            a = syscall(a, b, stack.rcx, stack.rdx, stack.rsi, stack.rdi, rbp, stack);
         }
 
         asm!("" : : "{rax}"(a) : : "intel", "volatile");
@@ -37,7 +33,11 @@ pub unsafe extern fn syscall() {
         mov fs, r11"
         : : : : "intel", "volatile");
 
-    inner();
+    // Get reference to stack variables
+    let rsp: usize;
+    asm!("" : "={rsp}"(rsp) : : : "intel", "volatile");
+
+    inner(&mut *(rsp as *mut SyscallStack));
 
     // Interrupt return
     asm!("pop fs
@@ -53,6 +53,23 @@ pub unsafe extern fn syscall() {
         : : : : "intel", "volatile");
 }
 
+#[allow(dead_code)]
+#[repr(packed)]
+pub struct SyscallStack {
+    pub fs: usize,
+    pub r11: usize,
+    pub r10: usize,
+    pub r9: usize,
+    pub r8: usize,
+    pub rsi: usize,
+    pub rdi: usize,
+    pub rdx: usize,
+    pub rcx: usize,
+    pub rip: usize,
+    pub cs: usize,
+    pub rflags: usize,
+}
+
 #[naked]
 pub unsafe extern fn clone_ret() -> usize {
     asm!("pop rbp"
diff --git a/src/macros.rs b/src/macros.rs
index a54fb35..2c8d133 100644
--- a/src/macros.rs
+++ b/src/macros.rs
@@ -85,7 +85,7 @@ macro_rules! interrupt_stack {
         #[naked]
         pub unsafe extern fn $name () {
             #[inline(never)]
-            unsafe fn inner($stack: &$crate::macros::InterruptStack) {
+            unsafe fn inner($stack: &mut $crate::macros::InterruptStack) {
                 $func
             }
 
@@ -109,7 +109,7 @@ macro_rules! interrupt_stack {
             asm!("" : "={rsp}"(rsp) : : : "intel", "volatile");
 
             // Call inner rust function
-            inner(&*(rsp as *const $crate::macros::InterruptStack));
+            inner(&mut *(rsp as *mut $crate::macros::InterruptStack));
 
             // Pop scratch registers and return
             asm!("pop fs
diff --git a/src/start.rs b/src/start.rs
index c7a6dd4..cd3c0c4 100644
--- a/src/start.rs
+++ b/src/start.rs
@@ -172,7 +172,7 @@ pub unsafe fn usermode(ip: usize, sp: usize, arg: usize) -> ! {
         :   "{r10}"(gdt::GDT_USER_DATA << 3 | 3), // Data segment
             "{r11}"(gdt::GDT_USER_TLS << 3 | 3), // TLS segment
             "{r12}"(sp), // Stack pointer
-            "{r13}"(3 << 12 | 1 << 9), // Flags - Set IOPL and interrupt enable flag
+            "{r13}"(0 << 12 | 1 << 9), // Flags - Set IOPL and interrupt enable flag
             "{r14}"(gdt::GDT_USER_CODE << 3 | 3), // Code segment
             "{r15}"(ip) // IP
             "{rdi}"(arg) // Argument
diff --git a/src/syscall/driver.rs b/src/syscall/driver.rs
index c28aa76..30f4492 100644
--- a/src/syscall/driver.rs
+++ b/src/syscall/driver.rs
@@ -1,8 +1,9 @@
+use interrupt::syscall::SyscallStack;
 use memory::{allocate_frames, deallocate_frames, Frame};
 use paging::{entry, ActivePageTable, PhysicalAddress, VirtualAddress};
 use context;
 use context::memory::Grant;
-use syscall::error::{Error, EFAULT, ENOMEM, EPERM, ESRCH, Result};
+use syscall::error::{Error, EFAULT, EINVAL, ENOMEM, EPERM, ESRCH, Result};
 use syscall::flag::{MAP_WRITE, MAP_WRITE_COMBINE};
 
 fn enforce_root() -> Result<()> {
@@ -16,10 +17,15 @@ fn enforce_root() -> Result<()> {
     }
 }
 
-pub fn iopl(_level: usize, _stack_base: usize) -> Result<usize> {
+pub fn iopl(level: usize, stack: &mut SyscallStack) -> Result<usize> {
     enforce_root()?;
 
-    //TODO
+    if level > 3 {
+        return Err(Error::new(EINVAL));
+    }
+
+    stack.rflags = (stack.rflags & !(3 << 12)) | ((level & 3) << 12);
+
     Ok(0)
 }
 
diff --git a/src/syscall/mod.rs b/src/syscall/mod.rs
index 8bfd132..77e6412 100644
--- a/src/syscall/mod.rs
+++ b/src/syscall/mod.rs
@@ -17,6 +17,7 @@ use self::error::{Error, Result, ENOSYS};
 use self::number::*;
 
 use context::ContextId;
+use interrupt::syscall::SyscallStack;
 use scheme::{FileHandle, SchemeNamespace};
 
 /// Driver syscalls
@@ -41,9 +42,9 @@ pub mod time;
 pub mod validate;
 
 #[no_mangle]
-pub extern fn syscall(a: usize, b: usize, c: usize, d: usize, e: usize, f: usize, stack: usize) -> usize {
+pub extern fn syscall(a: usize, b: usize, c: usize, d: usize, e: usize, f: usize, bp: usize, stack: &mut SyscallStack) -> usize {
     #[inline(always)]
-    fn inner(a: usize, b: usize, c: usize, d: usize, e: usize, f: usize, stack: usize) -> Result<usize> {
+    fn inner(a: usize, b: usize, c: usize, d: usize, e: usize, f: usize, bp: usize, stack: &mut SyscallStack) -> Result<usize> {
         match a & SYS_CLASS {
             SYS_CLASS_FILE => {
                 let fd = FileHandle::from(b);
@@ -83,7 +84,7 @@ pub extern fn syscall(a: usize, b: usize, c: usize, d: usize, e: usize, f: usize
                 SYS_BRK => brk(b),
                 SYS_GETPID => getpid().map(ContextId::into),
                 SYS_GETPPID => getppid().map(ContextId::into),
-                SYS_CLONE => clone(b, stack).map(ContextId::into),
+                SYS_CLONE => clone(b, bp).map(ContextId::into),
                 SYS_EXIT => exit((b & 0xFF) << 8),
                 SYS_KILL => kill(ContextId::from(b), c),
                 SYS_WAITPID => waitpid(ContextId::from(b), c, d).map(ContextId::into),
@@ -127,7 +128,7 @@ pub extern fn syscall(a: usize, b: usize, c: usize, d: usize, e: usize, f: usize
         }
     }
 
-    let result = inner(a, b, c, d, e, f, stack);
+    let result = inner(a, b, c, d, e, f, bp, stack);
 
     /*
     if let Err(ref err) = result {