diff --git a/common.c b/common.c
new file mode 100644
index 0000000..480d389
--- /dev/null
+++ b/common.c
@@ -0,0 +1,64 @@
+#include "common.h"
+
+void putchar(char ch);
+
+void printf(const char *fmt, ...) {
+  va_list vargs;
+  va_start(vargs, fmt);
+
+  while (*fmt) {
+    if (*fmt == '%') {
+      fmt++; // Skip '%'
+      switch (*fmt) { // Read the next character
+        case '\0': // '%' at the end of the format string
+          putchar('%');
+          goto end;
+        case '%': // Print '%'
+          putchar('%');
+          break;
+        case 's': { // Print a NULL-termintated string
+          const char *s = va_arg(vargs, const char *);
+          while (*s) {
+            putchar(*s);
+            s++;
+          }
+          break;
+        }
+        case 'd': { // Print an integer in decimal
+          int value = va_arg(vargs, int);
+          unsigned magnitude = value;
+          if (value < 0) {
+            putchar('-');
+            magnitude = -magnitude;
+          }
+
+          unsigned divisor = 1;
+          while (magnitude / divisor > 9)
+            divisor *= 10;
+
+          while (divisor > 0) {
+            putchar('0' + magnitude / divisor);
+            magnitude %= divisor;
+            divisor /= 10;
+          }
+
+          break;
+        }
+        case 'x': { // Print an integer in hexademical
+          unsigned value = va_arg(vargs, unsigned);
+          for (int i = 7; i >= 0; i--) {
+            unsigned nibble = (value >> (i * 4)) & 0xf;
+            putchar("0123456789abcdef"[nibble]);
+          }
+        }
+      }
+    } else {
+      putchar(*fmt);
+    }
+
+    fmt++;
+  }
+
+end:
+  va_end(vargs);
+}
diff --git a/common.h b/common.h
new file mode 100644
index 0000000..9adcc31
--- /dev/null
+++ b/common.h
@@ -0,0 +1,27 @@
+#pragma once
+
+typedef int bool;
+typedef unsigned char uint8_t;
+typedef unsigned short uint16_t;
+typedef unsigned int uint32_t;
+typedef unsigned long long uint64_t;
+typedef uint32_t size_t;
+typedef uint32_t paddr_t;
+typedef uint32_t vaddr_t;
+
+#define true 1
+#define false 0
+#define NULL ((void *) 0)
+#define align_up(value, align)    __builtin_align_up(value, align)
+#define is_aligned(value, align)  __builtin_is_aligned(value, align)
+#define offsetof(type, member)    __builtin_offsetof(type, member)
+#define va_list   __builtin_va_list
+#define va_start  __builtin_va_start
+#define va_end    __builtin_va_end
+#define va_arg    __builtin_va_arg
+
+void *memset(void *buf, char c, size_t n);
+void *memcpy(void *dst, const void *src, size_t n);
+char *strcpy(char *dst, const char *src);
+int strcmp(const char *s1, const char *s2);
+void printf(const char *fmt, ...);
diff --git a/kernel.c b/kernel.c
index 6abe1b7..0bc2384 100644
--- a/kernel.c
+++ b/kernel.c
@@ -1,28 +1,46 @@
-typedef unsigned char uint8_t;
-typedef unsigned int uint32_t;
-typedef uint32_t size_t;
+#include "kernel.h"
+#include "common.h"
 
 extern char __bss[], __bss_end[], __stack_top[];
 
-void *memset(void *buf, char c, size_t n) {
-    uint8_t *p = (uint8_t *) buf;
-    while (n--)
-        *p++ = c;
-    return buf;
+struct sbiret sbi_call(long arg0, long arg1, long arg2, long arg3, long arg4,
+                       long arg5, long fid, long eid) {
+    register long a0 __asm__("a0") = arg0;
+    register long a1 __asm__("a1") = arg1;
+    register long a2 __asm__("a2") = arg2;
+    register long a3 __asm__("a3") = arg3;
+    register long a4 __asm__("a4") = arg4;
+    register long a5 __asm__("a5") = arg5;
+    register long a6 __asm__("a6") = fid;
+    register long a7 __asm__("a7") = eid;
+
+    __asm__ __volatile__("ecall"
+                         : "=r"(a0), "=r"(a1)
+                         : "r"(a0), "r"(a1), "r"(a2), "r"(a3), "r"(a4), "r"(a5),
+                           "r"(a6), "r"(a7)
+                         : "memory");
+    return (struct sbiret){.error = a0, .value = a1};
+}
+
+void putchar(char ch) {
+    sbi_call(ch, 0, 0, 0, 0, 0, 0, 1 /* Console Putchar */);
 }
 
 void kernel_main(void) {
-    memset(__bss, 0, (size_t) __bss_end - (size_t) __bss);
-    
-    for (;;);
+    printf("\n\nHello %s\n", "RETARD!");
+    printf("60 + 9 = %d, %x\n", 60 + 9, 0x1234abcd);
+
+    for (;;) {
+        __asm__ __volatile__("wfi");
+    }
 }
 
 __attribute__((section(".text.boot")))
 __attribute__((naked))
 void boot(void) {
     __asm__ __volatile__(
-        "mv sp, %[stack_top]\n" // Set stacker point
-        "j kernel_main\n"       // Jump to the kernel function
+        "mv sp, %[stack_top]\n" // Set the stack pointer
+        "j kernel_main\n"       // Jump to the kernel main function
         :
         : [stack_top] "r" (__stack_top) // Pass the stack top address as %[stack_top]
     );
diff --git a/kernel.h b/kernel.h
new file mode 100644
index 0000000..4faa208
--- /dev/null
+++ b/kernel.h
@@ -0,0 +1,6 @@
+#pragma once
+
+struct sbiret {
+    long error;
+    long value;
+};
diff --git a/run.sh b/run.sh
index ad42e23..e312578 100755
--- a/run.sh
+++ b/run.sh
@@ -10,7 +10,7 @@ CFLAGS="-std=c11 -O2 -g3 -Wall -Wextra --target=riscv32-unknown-elf -fno-stack-p
 
 # Build the kernel
 $CC $CFLAGS -Wl,-Tkernel.ld -Wl,-Map=kernel.map -o kernel.elf \
-    kernel.c
+    kernel.c common.c
 
 # Start QEMU
 $QEMU -machine virt -bios default -nographic -serial mon:stdio --no-reboot \