diff --git a/build.sh b/build.sh
index fa85160..2876036 100755
--- a/build.sh
+++ b/build.sh
@@ -4,11 +4,19 @@ if [ -z "${MACH}" ]; then
     MACH=rpi3b
 fi
 
+if [ -z "${PROFILE}" ]; then
+    PROFILE=debug
+fi
+
 LLVM_DIR=$(llvm-config --bindir)
 ARCH=aarch64-unknown-none-${MACH}
 CARGO_ARGS="--target ../etc/aarch64-unknown-none-$MACH.json \
             --features mach_$MACH,fdt-rs"
 
+if [ "$PROFILE" = "release" ]; then
+    CARGO_ARGS="$CARGO_ARGS --release"
+fi
+
 set -e
 
 cd kernel
@@ -21,4 +29,5 @@ case $1 in
         ;;
 esac
 cd ..
-${LLVM_DIR}/llvm-objcopy -O binary target/${ARCH}/debug/kernel target/${ARCH}/debug/kernel.bin
+${LLVM_DIR}/llvm-objcopy -O binary target/${ARCH}/${PROFILE}/kernel \
+                                   target/${ARCH}/${PROFILE}/kernel.bin
diff --git a/kernel/src/arch/cpu.rs b/kernel/src/arch/cpu.rs
index fc66721..f853654 100644
--- a/kernel/src/arch/cpu.rs
+++ b/kernel/src/arch/cpu.rs
@@ -8,9 +8,9 @@ pub struct Cpu {
     index: u32, // 0x00
 }
 
-#[repr(transparent)]
 pub struct CpuRef {
     inner: &'static mut Cpu,
+    irq_state: usize
 }
 
 impl Cpu {
@@ -30,16 +30,19 @@ impl Cpu {
 
     #[inline]
     pub fn get() -> CpuRef {
-        // TODO lock
+        let irq_state = unsafe { intrin::save_irq() };
         CpuRef {
             inner: unsafe { Self::get_raw() },
+            irq_state
         }
     }
 }
 
 impl Drop for CpuRef {
     fn drop(&mut self) {
-        // TODO release
+        unsafe {
+            intrin::restore_irq(self.irq_state);
+        }
     }
 }
 
diff --git a/kernel/src/arch/intrin.rs b/kernel/src/arch/intrin.rs
index aa24a02..b50e53e 100644
--- a/kernel/src/arch/intrin.rs
+++ b/kernel/src/arch/intrin.rs
@@ -8,6 +8,21 @@ pub unsafe fn enable_irq() {
     llvm_asm!("msr daifclr, #0xF");
 }
 
+#[inline(always)]
+pub unsafe fn save_irq() -> usize {
+    let mut out: usize;
+    llvm_asm!(r#"
+        mrs $0, daif
+        msr daifset, #0xF
+    "#:"=r"(out));
+    out
+}
+
+#[inline(always)]
+pub unsafe fn restore_irq(state: usize) {
+    llvm_asm!("msr daif, $0"::"r"(state));
+}
+
 #[inline(always)]
 pub fn nop() {
     unsafe {
diff --git a/kernel/src/arch/mach_bcm283x/aux.rs b/kernel/src/arch/mach_bcm283x/aux.rs
index 0071d43..422f125 100644
--- a/kernel/src/arch/mach_bcm283x/aux.rs
+++ b/kernel/src/arch/mach_bcm283x/aux.rs
@@ -12,7 +12,7 @@ impl Aux {
     const AUX_ENABLES_MUART: u32 = 1 << 0;
 
     pub unsafe fn enable_uart(&self) {
-        let tmp = mmio_read(Self::REG_AUX_ENABLES);
+        let tmp: u32 = mmio_read(Self::REG_AUX_ENABLES);
         mmio_write(Self::REG_AUX_ENABLES, tmp | Self::AUX_ENABLES_MUART);
     }
 }
@@ -61,7 +61,7 @@ impl SerialDevice for AuxUart {
 
 impl InterruptHandler for AuxUart {
     fn do_irq(&self, _irq: u32) {
-        let _byte = unsafe { mmio_read(Self::REG_AUX_MU_IO) } as u8;
+        let _byte = unsafe { mmio_read::<u32>(Self::REG_AUX_MU_IO) } as u8;
     }
 }
 
diff --git a/kernel/src/arch/mach_bcm283x/intc.rs b/kernel/src/arch/mach_bcm283x/intc.rs
index ac7d332..6a344e7 100644
--- a/kernel/src/arch/mach_bcm283x/intc.rs
+++ b/kernel/src/arch/mach_bcm283x/intc.rs
@@ -59,7 +59,7 @@ impl InterruptController for Qa7Intc {
         match irq {
             super::IRQ_LOCAL_TIMER => {
                 let phys_core_id = cpu::get_phys_id();
-                let tmp = mmio_read(Self::REG_TIMER_INTC + 4 * phys_core_id);
+                let tmp: u32 = mmio_read(Self::REG_TIMER_INTC + 4 * phys_core_id);
                 mmio_write(
                     Self::REG_TIMER_INTC + 4 * phys_core_id,
                     tmp | Self::INTC_CNTPNSIRQ_IRQ,
@@ -74,7 +74,7 @@ impl InterruptController for Qa7Intc {
     }
 
     fn is_irq_pending(&self, irq: u32) -> bool {
-        unsafe { mmio_read(Self::REG_INT_SRC) & (1 << irq) != 0 }
+        unsafe { mmio_read::<u32>(Self::REG_INT_SRC) & (1 << irq) != 0 }
     }
 
     unsafe fn clear_irq(&self, _irq: u32) {}
@@ -95,9 +95,9 @@ impl InterruptController for Bcm2837Intc {
 
     fn is_irq_pending(&self, irq: u32) -> bool {
         if irq < 32 {
-            unsafe { mmio_read(Self::REG_PENDING_IRQ1) & (1 << irq) != 0 }
+            unsafe { mmio_read::<u32>(Self::REG_PENDING_IRQ1) & (1 << irq) != 0 }
         } else if irq < 64 {
-            unsafe { mmio_read(Self::REG_PENDING_IRQ2) & (1 << (irq - 32)) != 0 }
+            unsafe { mmio_read::<u32>(Self::REG_PENDING_IRQ2) & (1 << (irq - 32)) != 0 }
         } else {
             false
         }
diff --git a/kernel/src/arch/mach_bcm283x/mbox.rs b/kernel/src/arch/mach_bcm283x/mbox.rs
index 1f7a8f5..b57af17 100644
--- a/kernel/src/arch/mach_bcm283x/mbox.rs
+++ b/kernel/src/arch/mach_bcm283x/mbox.rs
@@ -1,5 +1,8 @@
 use crate::{
-    arch::{cpu, intrin, mmio_read, mmio_write, smp::{self, IpiDelivery, IpiMessage}},
+    arch::{
+        cpu, intrin, mmio_read, mmio_write,
+        smp::{self, IpiDelivery, IpiMessage},
+    },
     KernelSpace,
 };
 use address::{PhysicalAddress, VirtualAddress};
@@ -44,7 +47,10 @@ impl IpiDelivery for CoreMailbox {
 
     fn send_ipi(target_id: u32, message: IpiMessage) {
         unsafe {
-            mmio_write(Self::REG_SET + target_id as usize * 16, 1 << (message as u32));
+            mmio_write(
+                Self::REG_SET + target_id as usize * 16,
+                1 << (message as u32),
+            );
         }
     }
 }
@@ -56,21 +62,21 @@ impl CoreMailbox {
 
     pub fn do_irq(&self) {
         let phys_core_id = cpu::get_phys_id();
-        let value = unsafe { mmio_read(Self::REG_RDCLR + phys_core_id * 16 + self.index * 4) };
+        let value: u32 = unsafe { mmio_read(Self::REG_RDCLR + phys_core_id * 16 + self.index * 4) };
         if value != 0 {
             macro_rules! test_ipi {
                 ($value:expr, $msg:expr) => {
                     if $value & (1 << ($msg as u32)) != 0 {
                         smp::handle_ipi($msg);
                     }
-                }
+                };
             }
 
             test_ipi!(value, IpiMessage::Halt);
             test_ipi!(value, IpiMessage::Tick);
 
             unsafe {
-                mmio_write(
+                mmio_write::<u32>(
                     Self::REG_RDCLR + phys_core_id * 16 + self.index * 4,
                     0xFFFFFFFF,
                 );
@@ -85,7 +91,7 @@ unsafe fn call(ch: u32) -> Result<(), ()> {
     )) as u32)
         | (ch & 0xF);
 
-    while mmio_read(MBOX_STATUS) & MBOX_STATUS_FULL != 0 {
+    while mmio_read::<u32>(MBOX_STATUS) & MBOX_STATUS_FULL != 0 {
         llvm_asm!("nop");
     }
 
@@ -93,11 +99,11 @@ unsafe fn call(ch: u32) -> Result<(), ()> {
     mmio_write(MBOX_WRITE, value);
 
     loop {
-        while mmio_read(MBOX_STATUS) & MBOX_STATUS_EMPTY != 0 {
+        while mmio_read::<u32>(MBOX_STATUS) & MBOX_STATUS_EMPTY != 0 {
             llvm_asm!("nop");
         }
 
-        if mmio_read(MBOX_READ) == value {
+        if mmio_read::<u32>(MBOX_READ) == value {
             if MESSAGE.data[1] == MBOX_RESPONSE {
                 return Ok(());
             } else {
diff --git a/kernel/src/arch/macros.S b/kernel/src/arch/macros.S
index 32571d1..b31c0ec 100644
--- a/kernel/src/arch/macros.S
+++ b/kernel/src/arch/macros.S
@@ -28,62 +28,4 @@
 .set PAGE_ATTR_SHIFT,   2
 
 .set KERNEL_OFFSET, 0xFFFFFF8000000000
-
-.macro __exc_save_ctx
-    sub sp, sp, #192
-
-    stp x0, x1, [sp, #0]
-    stp x2, x3, [sp, #16]
-    stp x4, x5, [sp, #32]
-    stp x6, x7, [sp, #48]
-    stp x8, x9, [sp, #64]
-    stp x10, x11, [sp, #80]
-    stp x12, x13, [sp, #96]
-    stp x14, x15, [sp, #112]
-    stp x16, x17, [sp, #128]
-    stp x18, x29, [sp, #144]
-
-    mrs x0, elr_el1
-    stp x30, x0, [sp, #160]
-.endm
-
-.macro __exc_restore_ctx
-    ldp x30, x0, [sp, #160]
-    msr elr_el1, x0
-
-    ldp x0, x1, [sp, #0]
-    ldp x2, x3, [sp, #16]
-    ldp x4, x5, [sp, #32]
-    ldp x6, x7, [sp, #48]
-    ldp x8, x9, [sp, #64]
-    ldp x10, x11, [sp, #80]
-    ldp x12, x13, [sp, #96]
-    ldp x14, x15, [sp, #112]
-    ldp x16, x17, [sp, #128]
-    ldp x18, x29, [sp, #144]
-
-    add sp, sp, #192
-.endm
-
-.macro __callee_save_ctx
-    sub sp, sp, #96
-
-    stp x19, x20, [sp, #0]
-    stp x21, x22, [sp, #16]
-    stp x23, x24, [sp, #32]
-    stp x25, x26, [sp, #48]
-    stp x27, x29, [sp, #64]
-    stp xzr, lr, [sp, #80]
-.endm
-
-.macro __callee_restore_ctx
-    ldp x19, x20, [sp, #0]
-    ldp x21, x22, [sp, #16]
-    ldp x23, x24, [sp, #32]
-    ldp x25, x26, [sp, #48]
-    ldp x27, x29, [sp, #64]
-    ldp xzr, lr, [sp, #80]
-
-    add sp, sp, #96
-.endm
 .endif
diff --git a/kernel/src/arch/vectors.S b/kernel/src/arch/vectors.S
index 320347f..4cf0d92 100644
--- a/kernel/src/arch/vectors.S
+++ b/kernel/src/arch/vectors.S
@@ -1,5 +1,63 @@
 .include "kernel/src/arch/macros.S"
 
+.macro __exc_save_ctx
+    sub sp, sp, #192
+
+    stp x0, x1, [sp, #0]
+    stp x2, x3, [sp, #16]
+    stp x4, x5, [sp, #32]
+    stp x6, x7, [sp, #48]
+    stp x8, x9, [sp, #64]
+    stp x10, x11, [sp, #80]
+    stp x12, x13, [sp, #96]
+    stp x14, x15, [sp, #112]
+    stp x16, x17, [sp, #128]
+    stp x18, x29, [sp, #144]
+
+    mrs x0, elr_el1
+    stp x30, x0, [sp, #160]
+.endm
+
+.macro __exc_restore_ctx
+    ldp x30, x0, [sp, #160]
+    msr elr_el1, x0
+
+    ldp x0, x1, [sp, #0]
+    ldp x2, x3, [sp, #16]
+    ldp x4, x5, [sp, #32]
+    ldp x6, x7, [sp, #48]
+    ldp x8, x9, [sp, #64]
+    ldp x10, x11, [sp, #80]
+    ldp x12, x13, [sp, #96]
+    ldp x14, x15, [sp, #112]
+    ldp x16, x17, [sp, #128]
+    ldp x18, x29, [sp, #144]
+
+    add sp, sp, #192
+.endm
+
+.macro __callee_save_ctx
+    sub sp, sp, #96
+
+    stp x19, x20, [sp, #0]
+    stp x21, x22, [sp, #16]
+    stp x23, x24, [sp, #32]
+    stp x25, x26, [sp, #48]
+    stp x27, x29, [sp, #64]
+    stp xzr, lr, [sp, #80]
+.endm
+
+.macro __callee_restore_ctx
+    ldp x19, x20, [sp, #0]
+    ldp x21, x22, [sp, #16]
+    ldp x23, x24, [sp, #32]
+    ldp x25, x26, [sp, #48]
+    ldp x27, x29, [sp, #64]
+    ldp xzr, lr, [sp, #80]
+
+    add sp, sp, #96
+.endm
+
 .section .rodata
 .global el1_vectors
 .p2align 7
diff --git a/kernel/src/proc/mod.rs b/kernel/src/proc/mod.rs
new file mode 100644
index 0000000..a0f3dd1
--- /dev/null
+++ b/kernel/src/proc/mod.rs
@@ -0,0 +1,3 @@
+pub mod sched;
+
+pub struct Process {}
diff --git a/kernel/src/proc/sched.rs b/kernel/src/proc/sched.rs
new file mode 100644
index 0000000..5fb6a01
--- /dev/null
+++ b/kernel/src/proc/sched.rs
@@ -0,0 +1,5 @@
+pub struct Queue {}
+
+pub struct Scheduler {
+    queue: Queue,
+}
diff --git a/qemu.sh b/qemu.sh
index 9cf5893..e85ff29 100755
--- a/qemu.sh
+++ b/qemu.sh
@@ -6,12 +6,16 @@ if [ -z "${MACH}" ]; then
     MACH=rpi3b
 fi
 
+if [ -z "${PROFILE}" ]; then
+    PROFILE=debug
+fi
+
 if [ -z "$QEMU_BIN" ]; then
     QEMU_BIN=qemu-system-aarch64
 fi
 
 ARCH=aarch64-unknown-none-${MACH}
-KERNEL=target/${ARCH}/debug/kernel
+KERNEL=target/${ARCH}/${PROFILE}/kernel
 
 QEMU_OPTS="-chardev stdio,wait=off,id=char0,mux=on \
            -mon chardev=char0"