Write a simple bootstrap stub

nob.c

@@ -12,8 +12,11 @@ int main(int argc, char **argv) {
 
     Nob_Cmd cmd = {0};
 
-    nob_cmd_append(&cmd, "cc", "-Wall", "-Wextra", "-o", BUILD_FOLDER "kernel", SRC_FOLDER "kernel.c");
+    nob_cmd_append(&cmd, "i686-elf-as", "-o", BUILD_FOLDER "boot.o", SRC_FOLDER "boot.s");
+    if (!nob_cmd_run(&cmd))
+        return 1;
 
+    nob_cmd_append(&cmd, "i686-elf-gcc", "-Wall", "-Wextra", "-o", BUILD_FOLDER "kernel", SRC_FOLDER "kernel.c");
     if (!nob_cmd_run(&cmd))
         return 1;
 

shell.nix

@@ -0,0 +1,10 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+pkgs.mkShell {
+  nativeBuildInputs =
+    with pkgs; [
+      pkgsCross.i686-embedded.buildPackages.gcc
+      pkgsCross.i686-embedded.buildPackages.binutils
+      gdb
+    ];
+}

src/boot.s

@@ -0,0 +1,34 @@
+/* Multiboot header */
+	.set ALIGN, 	1<<0
+	.set MEMINFO, 	1<<1
+	.set FLAGS, 	ALIGN | MEMINFO
+	.set MAGIC, 	0x1BADB002
+	.set CHECKSUM, 	-(MAGIC + FLAGS)
+
+	.section .multiboot
+	.align 4
+	.long MAGIC
+	.long FLAGS
+	.long CHECKSUM
+
+	.section .bss
+	.align 16
+stack_bottom:
+	.skip 16384 /* 16 KiB */
+stack_top:
+
+	.section .text
+	.global _start
+	.type _start, @function
+_start:
+	mov $stack_top, %esp
+
+	/* Initialize processor state here */
+
+	call kernel_main
+
+	cli /* Disable interrupts */
+1:	hlt /* Waits for an interrupt */
+	jmp 1b /* Jump in case an interrupt actually arrives */
+
+	.size _start, . - _start