From e0979ed357e745eeb64176c5e8337f7eb8c65d4c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Thomas=20Lov=C3=A9n?= <thomasloven@gmail.com>
Date: Sun, 2 Jan 2022 17:25:07 +0100
Subject: [PATCH] Bootable multiboot2 kernel

---
 .gitignore                         |  7 ++++++-
 Makefile                           | 10 +++++++++
 make                               |  2 +-
 src/kernel/Link.ld                 | 10 +++++++++
 src/kernel/Makefile                | 33 ++++++++++++++++++++++++++++++
 src/kernel/boot/boot.S             |  7 +++++++
 src/kernel/boot/multiboot_header.S | 15 ++++++++++++++
 src/kernel/include/multiboot.h     |  7 +++++++
 toolchain/gdbinit                  |  5 +++++
 toolchain/setup-grub.sh            | 13 ++++++++++++
 10 files changed, 107 insertions(+), 2 deletions(-)
 create mode 100644 src/kernel/Link.ld
 create mode 100644 src/kernel/Makefile
 create mode 100644 src/kernel/boot/boot.S
 create mode 100644 src/kernel/boot/multiboot_header.S
 create mode 100644 src/kernel/include/multiboot.h
 create mode 100755 toolchain/setup-grub.sh

diff --git a/.gitignore b/.gitignore
index 840d338..501990d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,8 @@
 dist/
 build/
-sysroot/
\ No newline at end of file
+sysroot/
+
+*.d
+*.o
+
+src/kernel/kernel
\ No newline at end of file
diff --git a/Makefile b/Makefile
index 6328a18..07dbace 100644
--- a/Makefile
+++ b/Makefile
@@ -7,8 +7,18 @@ SYSROOT := $(BUILDROOT)/sysroot
 DIST := $(BUILDROOT)/dist/mittos.iso
 
 $(DIST):
+	setup-grub.sh
 	grub-mkrescue -o $@ $(SYSROOT)
 
+kernel:
+ifeq ($(shell make -sqC src/kernel || echo 1), 1)
+	$(MAKE) -C src/kernel install
+endif
+
 install: $(DIST)
 
+clean:
+	rm -rf $(DIST)
+	$(MAKE) -C src/kernel clean
+
 .PHONY: install
\ No newline at end of file
diff --git a/make b/make
index dd1199d..596a495 100755
--- a/make
+++ b/make
@@ -1,3 +1,3 @@
 #!/usr/bin/env bash
 
-docker-compose -f toolchain/docker-compose.yml run --rm make "$@"
\ No newline at end of file
+docker-compose -f toolchain/docker-compose.yml run --rm -u $(id -u):$(id -g) make make "$@"
\ No newline at end of file
diff --git a/src/kernel/Link.ld b/src/kernel/Link.ld
new file mode 100644
index 0000000..ed6473f
--- /dev/null
+++ b/src/kernel/Link.ld
@@ -0,0 +1,10 @@
+ENTRY(_start)
+
+SECTIONS
+{
+    .text :
+    {
+        *(.multiboot)
+        *(.text)
+    }
+}
\ No newline at end of file
diff --git a/src/kernel/Makefile b/src/kernel/Makefile
new file mode 100644
index 0000000..6a9b12a
--- /dev/null
+++ b/src/kernel/Makefile
@@ -0,0 +1,33 @@
+
+CC := x86_64-elf-gcc
+
+SRC := $(wildcard **/*.[cS])
+OBJ := $(patsubst %, %.o, $(basename $(SRC)))
+
+CFLAGS := -Wall -Wextra -pedantic -ffreestanding
+CFLAGS += -ggdb -O0
+ASFLAGS += -ggdb
+CPPFLAGS += -I include
+LDFLAGS := -n -nostdlib -lgcc -T Link.ld
+
+kernel: $(OBJ)
+	$(LINK.c) $^ -o $@
+
+DEP := $(OBJ:.o=.d)
+DEPFLAGS = -MT $@ -MMD -MP -MF $*.d
+$(OBJ): CPPFLAGS += $(DEPFLAGS)
+%.d: ;
+
+DESTDIR ?= $(BUILDROOT)/sysroot
+
+$(DESTDIR)$(PREFIX)/kernel: kernel
+	install -D kernel $(DESTDIR)$(PREFIX)/kernel
+
+install: $(DESTDIR)$(PREFIX)/kernel
+
+clean:
+	rm -rf $(OBJ) $(DEP) kernel
+
+.PHONY: install
+
+include $(DEP)
\ No newline at end of file
diff --git a/src/kernel/boot/boot.S b/src/kernel/boot/boot.S
new file mode 100644
index 0000000..9df8fd3
--- /dev/null
+++ b/src/kernel/boot/boot.S
@@ -0,0 +1,7 @@
+.intel_syntax noprefix
+.section .text
+.global _start
+.code32
+_start:
+cli
+jmp $
\ No newline at end of file
diff --git a/src/kernel/boot/multiboot_header.S b/src/kernel/boot/multiboot_header.S
new file mode 100644
index 0000000..ba08c0a
--- /dev/null
+++ b/src/kernel/boot/multiboot_header.S
@@ -0,0 +1,15 @@
+#include <multiboot.h>
+.section .multiboot
+
+.align 0x8
+Multiboot2Header:
+.long MBOOT2_MAGIC
+.long MBOOT2_ARCH
+.long MBOOT2_LENGTH
+.long MBOOT2_CHECKSUM
+
+.short 0
+.short 0
+.long 8
+
+Multiboot2HeaderEnd:
\ No newline at end of file
diff --git a/src/kernel/include/multiboot.h b/src/kernel/include/multiboot.h
new file mode 100644
index 0000000..9964bd1
--- /dev/null
+++ b/src/kernel/include/multiboot.h
@@ -0,0 +1,7 @@
+#pragma once
+
+#define MBOOT2_MAGIC 0xE85250D6
+#define MBOOT2_REPLY 0x36D76289
+#define MBOOT2_ARCH 0
+#define MBOOT2_LENGTH (Multiboot2HeaderEnd - Multiboot2Header)
+#define MBOOT2_CHECKSUM -(MBOOT2_MAGIC + MBOOT2_ARCH + MBOOT2_LENGTH)
diff --git a/toolchain/gdbinit b/toolchain/gdbinit
index 4c381b6..45fd97e 100644
--- a/toolchain/gdbinit
+++ b/toolchain/gdbinit
@@ -13,4 +13,9 @@ end
 
 define reset
 monitor system_reset
+end
+
+python
+import os
+gdb.execute('file ' + os.environ['BUILDROOT'] + '/sysroot/kernel')
 end
\ No newline at end of file
diff --git a/toolchain/setup-grub.sh b/toolchain/setup-grub.sh
new file mode 100755
index 0000000..753806e
--- /dev/null
+++ b/toolchain/setup-grub.sh
@@ -0,0 +1,13 @@
+#!/bin/sh
+
+mkdir -p ${BUILDROOT}/sysroot/boot/grub
+
+cat > ${BUILDROOT}/sysroot/boot/grub/grub.cfg << EOF
+set timeout=1
+set default=0
+
+menuentry "mittos64" {
+    multiboot2 /kernel
+}
+
+EOF
\ No newline at end of file