Building a multiboot 1 compatible executable

src/kernel/Link.ld

@@ -0,0 +1,11 @@
+ENTRY(_start)
+
+SECTIONS
+{
+  .text : AT(ADDR(.text))
+  {
+    *(.multiboot)
+    *(.text)
+    . = ALIGN(4096);
+  }
+}

src/kernel/Makefile

@@ -0,0 +1,19 @@
+ifeq ($(MITTOS64),)
+$(error Unsupported environment! See README)
+endif
+
+CC := x86_64-elf-gcc
+
+SRC := $(wildcard **/*.[cS])
+OBJ := $(patsubst %, %.o, $(basename $(SRC)))
+
+CFLAGS ?= -Wall -Wextra
+CFLAGS += -ffreestanding
+
+all: kernel
+
+kernel: LDFLAGS += -n -nostdlib -T Link.ld
+kernel: $(OBJ)
+	$(LINK.c) $^ -o $@
+	mkdir -p /opt/sysroot
+	cp kernel /opt/sysroot/kernel

src/kernel/boot/boot.S

@@ -0,0 +1,26 @@
+#define MBOOT1_MAGIC 0x1BADB002
+#define MBOOT1_PALIGN 0x01
+#define MBOOT1_MEMINFO 0x02
+#define MBOOT1_FLAGS (MBOOT1_PALIGN | MBOOT1_MEMINFO)
+#define MBOOT1_CS -(MBOOT1_FLAGS + MBOOT1_MAGIC)
+
+.intel_syntax noprefix
+
+.section .multiboot
+.align 0x1000
+MultiBootHeader1:
+.long MBOOT1_MAGIC
+.long MBOOT1_FLAGS
+.long MBOOT1_CS
+
+.section .text
+.global _start
+.code32
+_start:
+cli
+
+// Print a red exclamation mark in top left corner
+mov eax, 0x0421
+mov short [0xB8000], ax
+// and loop infinitely
+jmp $