diff --git a/Cargo.lock b/Cargo.lock
index 4d5dc3a..5bb038f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -64,6 +64,9 @@ dependencies = [
 [[package]]
 name = "init"
 version = "0.1.0"
+dependencies = [
+ "libusr",
+]
 
 [[package]]
 name = "kernel"
@@ -77,6 +80,10 @@ dependencies = [
  "tock-registers",
 ]
 
+[[package]]
+name = "libusr"
+version = "0.1.0"
+
 [[package]]
 name = "memoffset"
 version = "0.5.6"
diff --git a/Cargo.toml b/Cargo.toml
index 540262c..bbf5076 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -10,6 +10,7 @@ edition = "2018"
 [workspace]
 members = [
     "kernel",
+    "libusr",
     "init",
     "error"
 ]
diff --git a/Makefile b/Makefile
index 26f408e..9861b99 100644
--- a/Makefile
+++ b/Makefile
@@ -58,7 +58,7 @@ all: kernel
 
 kernel:
 	cd kernel && cargo build $(CARGO_BUILD_OPTS)
-	cd init && cargo build --target=../etc/$(ARCH)-osdev5.json -Z build-std=core
+	cd init && cargo build --target=../etc/$(ARCH)-osdev5.json -Z build-std=core,alloc,compiler_builtins
 	cp target/$(ARCH)-osdev5/debug/init $(O)/initrd.img
 ifeq ($(ARCH),aarch64)
 	$(LLVM_BASE)/llvm-strip -o $(O)/kernel.strip $(O)/kernel
diff --git a/init/Cargo.toml b/init/Cargo.toml
index f922052..a687bfa 100644
--- a/init/Cargo.toml
+++ b/init/Cargo.toml
@@ -6,3 +6,4 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+libusr = { path = "../libusr" }
diff --git a/init/src/main.rs b/init/src/main.rs
index dc8a51c..21b1a8e 100644
--- a/init/src/main.rs
+++ b/init/src/main.rs
@@ -1,27 +1,11 @@
-#![feature(asm)]
 #![no_std]
 #![no_main]
 
-use core::panic::PanicInfo;
+#[macro_use]
+extern crate libusr;
 
-#[link_section = ".text._start"]
 #[no_mangle]
-extern "C" fn _start(arg: usize) -> ! {
-    let mut c0 = arg;
-    let mut c1: usize;
-    loop {
-        unsafe {
-            asm!("mrs {}, cntpct_el0", out(reg) c1);
-            asm!("svc #0", inout("x0") c0, in("x1") c1);
-        }
-
-        for _ in 0..1000000 {
-            unsafe { asm!("nop"); }
-        }
-    }
-}
-
-#[panic_handler]
-fn panic_handler(_pi: &PanicInfo) -> ! {
-    loop {}
+fn main() -> i32 {
+    trace!("Hello from userspace");
+    123
 }
diff --git a/kernel/src/arch/aarch64/exception.rs b/kernel/src/arch/aarch64/exception.rs
index 3e3fb2d..29d16d8 100644
--- a/kernel/src/arch/aarch64/exception.rs
+++ b/kernel/src/arch/aarch64/exception.rs
@@ -3,6 +3,7 @@
 use crate::arch::machine;
 use crate::debug::Level;
 use crate::dev::irq::{IntController, IrqContext};
+use crate::syscall;
 use cortex_a::registers::{ESR_EL1, FAR_EL1};
 use tock_registers::interfaces::Readable;
 
@@ -18,7 +19,7 @@ pub const EC_SVC_AA64: u64 = 0b010101;
 #[derive(Debug)]
 #[repr(C)]
 struct ExceptionFrame {
-    x: [u64; 32],
+    x: [usize; 32],
     spsr_el1: u64,
     elr_el1: u64,
     sp_el0: u64,
@@ -81,8 +82,12 @@ extern "C" fn __aa64_exc_sync_handler(exc: &mut ExceptionFrame) {
             dump_data_abort(Level::Error, esr, far);
         }
         EC_SVC_AA64 => {
-            infoln!("{:#x} {:#x}", exc.x[0], exc.x[1]);
-            exc.x[0] += 1;
+            unsafe {
+                match syscall::syscall(exc.x[8], &exc.x[..6]) {
+                    Ok(val) => exc.x[0] = val,
+                    Err(_) => exc.x[0] = usize::MAX,
+                }
+            }
             return;
         }
         _ => {}
diff --git a/kernel/src/main.rs b/kernel/src/main.rs
index b2e164c..853d519 100644
--- a/kernel/src/main.rs
+++ b/kernel/src/main.rs
@@ -31,6 +31,8 @@ pub mod mem;
 pub mod proc;
 pub mod sync;
 pub mod util;
+#[allow(missing_docs)]
+pub mod syscall;
 
 #[panic_handler]
 fn panic_handler(pi: &core::panic::PanicInfo) -> ! {
diff --git a/kernel/src/proc/mod.rs b/kernel/src/proc/mod.rs
index ab3eb50..576364f 100644
--- a/kernel/src/proc/mod.rs
+++ b/kernel/src/proc/mod.rs
@@ -57,13 +57,15 @@ pub unsafe fn enter(initrd: Option<(usize, usize)>) -> ! {
     if let Some((start, end)) = initrd {
         let initrd = Box::into_raw(Box::new((mem::virtualize(start), mem::virtualize(end))));
 
-        spawn!(fn (initrd_ptr: usize) {
-            debugln!("Running kernel init process");
+        for _ in 0..4 {
+            spawn!(fn (initrd_ptr: usize) {
+                debugln!("Running kernel init process");
 
-            let (start, _end) = unsafe { *(initrd_ptr as *const (usize, usize)) };
-            Process::execve(|space| elf::load_elf(space, start as *const u8), 0).unwrap();
-            panic!("This code should not run");
-        }, initrd as usize);
+                let (start, _end) = unsafe { *(initrd_ptr as *const (usize, usize)) };
+                Process::execve(|space| elf::load_elf(space, start as *const u8), 0).unwrap();
+                panic!("This code should not run");
+            }, initrd as usize);
+        }
     }
     SCHED.enter();
 }
diff --git a/kernel/src/proc/process.rs b/kernel/src/proc/process.rs
index 8b272b2..672c6c4 100644
--- a/kernel/src/proc/process.rs
+++ b/kernel/src/proc/process.rs
@@ -125,6 +125,11 @@ impl Process {
     const USTACK_VIRT_TOP: usize = 0x100000000;
     const USTACK_PAGES: usize = 4;
 
+    /// Returns currently executing process
+    pub fn current() -> ProcessRef {
+        SCHED.current_process()
+    }
+
     /// Schedules an initial thread for execution
     ///
     /// # Safety
@@ -190,6 +195,7 @@ impl Process {
                 state: State::Ready,
             }),
         });
+        debugln!("New kernel process: {}", id);
         assert!(PROCESSES.lock().insert(id, res.clone()).is_none());
         Ok(res)
     }
@@ -263,10 +269,7 @@ impl Process {
                 old_pid,
                 lock.id
             );
-            assert!(
-                proc_lock.insert(lock.id, proc.clone()).is_none(),
-                "Failed to downgrade kernel process (add user pid)"
-            );
+            assert!(proc_lock.insert(lock.id, proc.clone()).is_none());
             unsafe {
                 SCHED.hack_current_pid(lock.id);
             }
diff --git a/kernel/src/proc/sched.rs b/kernel/src/proc/sched.rs
index f124fb4..3f2f598 100644
--- a/kernel/src/proc/sched.rs
+++ b/kernel/src/proc/sched.rs
@@ -66,7 +66,7 @@ impl Scheduler {
             PROCESSES.lock().get(&id).unwrap().clone()
         };
 
-        asm!("msr daifclr, #2");
+        asm!("msr daifset, #2");
         Process::enter(thread)
     }
 
@@ -103,7 +103,7 @@ impl Scheduler {
                 let lock = PROCESSES.lock();
                 (
                     lock.get(&current).unwrap().clone(),
-                    lock.get(&next).unwrap().clone(),
+                    lock.get(&next).unwrap().clone()
                 )
             };
 
@@ -112,7 +112,7 @@ impl Scheduler {
 
         if !Rc::ptr_eq(&from, &to) {
             unsafe {
-                asm!("msr daifclr, #2");
+                asm!("msr daifset, #2");
                 Process::switch(from, to, discard);
             }
         }
diff --git a/kernel/src/syscall.rs b/kernel/src/syscall.rs
new file mode 100644
index 0000000..7710812
--- /dev/null
+++ b/kernel/src/syscall.rs
@@ -0,0 +1,60 @@
+use crate::mem;
+use error::Errno;
+
+fn translate(virt: usize) -> Option<usize> {
+    let mut res: usize;
+    unsafe {
+        asm!("at s1e1r, {}; mrs {}, par_el1", in(reg) virt, out(reg) res);
+    }
+    if res & 1 == 0 {
+        Some(res & !(0xFFF | (0xFF << 56)))
+    } else {
+        None
+    }
+}
+
+fn validate_user_ptr(base: usize, len: usize) -> Result<(), Errno> {
+    if base > mem::KERNEL_OFFSET || base + len > mem::KERNEL_OFFSET {
+        warnln!("User region refers to kernel memory: base={:#x}, len={:#x}", base, len);
+        return Err(Errno::InvalidArgument);
+    }
+
+    for i in (base / mem::PAGE_SIZE)..((base + len + mem::PAGE_SIZE - 1) / mem::PAGE_SIZE) {
+        if translate(i * mem::PAGE_SIZE).is_none() {
+            warnln!(
+                "User region refers to unmapped memory: base={:#x}, len={:#x} (page {:#x})",
+                base,
+                len,
+                i * mem::PAGE_SIZE
+            );
+            return Err(Errno::InvalidArgument);
+        }
+    }
+
+    Ok(())
+}
+
+pub unsafe fn syscall(num: usize, args: &[usize]) -> Result<usize, Errno> {
+    match num {
+        // sys_exit
+        1 => {
+            use crate::proc::Process;
+            Process::current().exit(args[0] as i32);
+            unreachable!();
+        }
+        // sys_ex_debug_trace
+        120 => {
+            use crate::debug::Level;
+            validate_user_ptr(args[0], args[1])?;
+
+            let buf = core::slice::from_raw_parts(args[0] as *const u8, args[1]);
+            print!(Level::Debug, "[trace] ");
+            for &byte in buf.iter() {
+                print!(Level::Debug, "{}", byte as char);
+            }
+            println!(Level::Debug, "");
+            Ok(args[1])
+        }
+        _ => panic!("Undefined system call: {}", num),
+    }
+}
diff --git a/libusr/Cargo.toml b/libusr/Cargo.toml
new file mode 100644
index 0000000..714ee4e
--- /dev/null
+++ b/libusr/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "libusr"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/libusr/src/lib.rs b/libusr/src/lib.rs
new file mode 100644
index 0000000..5ae4587
--- /dev/null
+++ b/libusr/src/lib.rs
@@ -0,0 +1,29 @@
+#![feature(
+    asm,
+    alloc_error_handler,
+)]
+#![no_std]
+
+use core::panic::PanicInfo;
+
+mod sys;
+pub mod mem;
+pub mod os;
+
+#[link_section = ".text._start"]
+#[no_mangle]
+extern "C" fn _start(_arg: usize) -> ! {
+    extern "Rust" {
+        fn main() -> i32;
+    }
+    unsafe {
+        sys::sys_exit(main());
+    }
+}
+
+#[panic_handler]
+fn panic_handler(pi: &PanicInfo) -> ! {
+    // TODO formatted messages
+    trace!("Panic ocurred: {}", pi);
+    sys::sys_exit(-1);
+}
diff --git a/libusr/src/mem.rs b/libusr/src/mem.rs
new file mode 100644
index 0000000..6d667be
--- /dev/null
+++ b/libusr/src/mem.rs
@@ -0,0 +1,31 @@
+#[no_mangle]
+pub unsafe extern "C" fn memcpy(dst: *mut u8, src: *mut u8, mut len: usize) -> *mut u8 {
+    while len != 0 {
+        len -= 1;
+        *dst.add(len) = *src.add(len);
+    }
+    dst
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn memcmp(a: *mut u8, b: *mut u8, mut len: usize) -> isize {
+    while len != 0 {
+        len -= 1;
+        if *a.add(len) < *b.add(len) {
+            return -1;
+        }
+        if *a.add(len) > *b.add(len) {
+            return 1;
+        }
+    }
+    0
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn memset(buf: *mut u8, val: u8, mut len: usize) -> *mut u8 {
+    while len != 0 {
+        len -= 1;
+        *buf.add(len) = val;
+    }
+    buf
+}
diff --git a/libusr/src/os.rs b/libusr/src/os.rs
new file mode 100644
index 0000000..afbc0ca
--- /dev/null
+++ b/libusr/src/os.rs
@@ -0,0 +1,33 @@
+use crate::sys;
+use core::fmt;
+
+#[macro_export]
+macro_rules! trace {
+    ($($args:tt)+) => ($crate::os::_trace(format_args!($($args)+)))
+}
+
+struct BufferWriter<'a> {
+    buf: &'a mut [u8],
+    pos: usize,
+}
+
+impl fmt::Write for BufferWriter<'_> {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        for byte in s.bytes() {
+            self.buf[self.pos] = byte;
+            self.pos += 1;
+        }
+        Ok(())
+    }
+}
+
+pub fn _trace(args: fmt::Arguments) {
+    use core::fmt::Write;
+    static mut BUFFER: [u8; 4096] = [0; 4096];
+    let mut writer = BufferWriter {
+        buf: unsafe { &mut BUFFER },
+        pos: 0,
+    };
+    writer.write_fmt(args).ok();
+    sys::sys_ex_debug_trace(unsafe { &BUFFER } as *const _, writer.pos);
+}
diff --git a/libusr/src/sys.rs b/libusr/src/sys.rs
new file mode 100644
index 0000000..ba68e54
--- /dev/null
+++ b/libusr/src/sys.rs
@@ -0,0 +1,27 @@
+macro_rules! syscall {
+    ($num:expr, $a0:expr) => {{
+        let mut res: usize = $a0;
+        unsafe {
+            asm!("svc #0", inout("x0") res, in("x8") $num, options(nostack));
+        }
+        res
+    }};
+    ($num:expr, $a0:expr, $a1:expr) => {{
+        let mut res: usize = $a0;
+        unsafe {
+            asm!("svc #0", inout("x0") res, in("x1") $a1, in("x8") $num, options(nostack));
+        }
+        res
+    }};
+}
+
+#[inline(always)]
+pub fn sys_exit(status: i32) -> ! {
+    syscall!(1, status as usize);
+    loop {}
+}
+
+#[inline(always)]
+pub fn sys_ex_debug_trace(msg: *const u8, len: usize) -> usize {
+    syscall!(120, msg as usize, len)
+}