Setup simple kernel with Hello World output via debugcon (AI)

src/kernel.c

@@ -1,3 +1,31 @@
-void _start() {
-    while(1) {}
+#include <multiboot2.h>
+#include <stdint.h>
+#include <stddef.h>
+
+static inline void outb(uint16_t port, uint8_t val)
+{
+    asm volatile ( "outb %b0, %w1" : : "a"(val), "Nd"(port) );
+}
+
+void offset_print(const char *str)
+{
+    while (*str) {
+        outb(0xE9, *str);
+        str++;
+    }
+}
+
+#define MULTIBOOT_BOOTLOADER_MAGIC 0x2BADB002
+
+void kernel_main(uint32_t magic, uint32_t addr) {
+    (void)addr; // Unused for now
+
+    if (magic != MULTIBOOT2_BOOTLOADER_MAGIC && magic != MULTIBOOT_BOOTLOADER_MAGIC) {
+        offset_print("Invalid magic number: ");
+        // I don't have hex print yet, but I can print something generic
+        offset_print("Unknown\n");
+        return;
+    }
+
+    offset_print("Hello, world\n");
 }