Fix kernel entrypoint

kernel/src/main.rs

@@ -1,22 +1,31 @@
 #![no_std]
 #![no_main]
 
-use core::{arch::asm, panic::PanicInfo};
+use core::{
+    arch::{asm, global_asm},
+    panic::PanicInfo,
+};
 
 use gdt::setup_gdt;
 use log::{error, info};
 
 mod gdt;
 
-static mut STACK: [u8; 8 * 1024] = [0; 8 * 1024];
+global_asm!(
+    "
+    .global _start
+    _start:
+    mov $stack, %rsp
+    call main
+    .section .bss
+    .align 16
+    .skip 0x2000
+    stack:
+    ",
+    options(att_syntax)
+);
 
 #[no_mangle]
-fn _start() -> ! {
-    unsafe {
-        asm!("mov rsp, {}", in(reg) STACK.as_ptr().add(STACK.len()));
-    }
-    main();
-}
 fn main() -> ! {
     com_logger::init();
     info!("Starting kernel...");

qemu.sh

@@ -0,0 +1,5 @@
+#!/bin/sh
+# shellcheck disable=SC2068
+set -e
+./build.sh
+qemu-system-x86_64 -M q35 -m 256M -L /usr/share/OVMF -bios OVMF_CODE.fd -drive file=img/os.img,format=raw $@