From b83b28b21571f9b1fadd251295f5ca03d9dfedc7 Mon Sep 17 00:00:00 2001
From: Xander <xander@icth.xyz>
Date: Wed, 28 Jun 2023 17:20:46 +0200
Subject: Booting to protected mode

---
 .gitignore                           |  1 +
 Makefile                             | 36 +++++++++++++++++++++
 flake.lock                           | 61 ++++++++++++++++++++++++++++++++++++
 src/arch/x86_64/boot.asm             |  8 +++++
 src/arch/x86_64/grub.cfg             |  7 +++++
 src/arch/x86_64/linker.ld            | 16 ++++++++++
 src/arch/x86_64/multiboot_header.asm | 15 +++++++++
 7 files changed, 144 insertions(+)
 create mode 100644 Makefile
 create mode 100644 flake.lock
 create mode 100644 src/arch/x86_64/boot.asm
 create mode 100644 src/arch/x86_64/grub.cfg
 create mode 100644 src/arch/x86_64/linker.ld
 create mode 100644 src/arch/x86_64/multiboot_header.asm

diff --git a/.gitignore b/.gitignore
index 567609b..ff72c83 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 build/
+.ccls-cache/
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..6d4c9a8
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,36 @@
+arch ?= x86_64
+kernel := build/kernel-$(arch).bin
+iso := build/os-$(arch).iso
+
+linker_script := src/arch/$(arch)/linker.ld
+grub_cfg := src/arch/$(arch)/grub.cfg
+assembly_source_files := $(wildcard src/arch/$(arch)/*.asm)
+assembly_object_files := $(patsubst src/arch/$(arch)/%.asm, \
+	build/arch/$(arch)/%.o, $(assembly_source_files))
+
+.PHONY: all clean run iso
+
+all: $(kernel)
+
+clean:
+	@rm -r build
+
+run: $(iso)
+	@qemu-system-x86_64 -cdrom $(iso)
+
+iso: $(iso)
+
+$(iso): $(kernel) $(grub_cfg)
+	@mkdir -p build/isofiles/boot/grub
+	@cp $(kernel) build/isofiles/boot/kernel.bin
+	@cp $(grub_cfg) build/isofiles/boot/grub
+	@grub-mkrescue -o $(iso) build/isofiles 2> /dev/null
+	@rm -r build/isofiles
+
+$(kernel): $(assembly_object_files) $(linker_script)
+	@ld -n -T $(linker_script) -o $(kernel) $(assembly_object_files)
+
+# compile assembly files
+build/arch/$(arch)/%.o: src/arch/$(arch)/%.asm
+	@mkdir -p $(shell dirname $@)
+	@nasm -felf64 $< -o $@
diff --git a/flake.lock b/flake.lock
new file mode 100644
index 0000000..35ff5fb
--- /dev/null
+++ b/flake.lock
@@ -0,0 +1,61 @@
+{
+  "nodes": {
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1687709756,
+        "narHash": "sha256-Y5wKlQSkgEK2weWdOu4J3riRd+kV/VCgHsqLNTTWQ/0=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "dbabf0ca0c0c4bce6ea5eaf65af5cb694d2082c7",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1687886075,
+        "narHash": "sha256-PeayJDDDy+uw1Ats4moZnRdL1OFuZm1Tj+KiHlD67+o=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "a565059a348422af5af9026b5174dc5c0dcefdae",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
diff --git a/src/arch/x86_64/boot.asm b/src/arch/x86_64/boot.asm
new file mode 100644
index 0000000..1a531c0
--- /dev/null
+++ b/src/arch/x86_64/boot.asm
@@ -0,0 +1,8 @@
+global start
+
+section .text
+bits 32
+start:
+    ; print `OK` to screen
+    mov dword [0xb8000], 0x2f4b2f4f
+    hlt
diff --git a/src/arch/x86_64/grub.cfg b/src/arch/x86_64/grub.cfg
new file mode 100644
index 0000000..7c34c9c
--- /dev/null
+++ b/src/arch/x86_64/grub.cfg
@@ -0,0 +1,7 @@
+set timeout=0
+set default=0
+
+menuentry "ats-os" {
+    multiboot2 /boot/kernel.bin
+    boot
+}
diff --git a/src/arch/x86_64/linker.ld b/src/arch/x86_64/linker.ld
new file mode 100644
index 0000000..5d788f1
--- /dev/null
+++ b/src/arch/x86_64/linker.ld
@@ -0,0 +1,16 @@
+ENTRY(start)
+
+SECTIONS {
+    . = 1M;
+
+    .boot :
+    {
+        /* ensure that the multiboot header is at the beginning */
+        *(.multiboot_header)
+    }
+
+    .text :
+    {
+        *(.text)
+    }
+}
diff --git a/src/arch/x86_64/multiboot_header.asm b/src/arch/x86_64/multiboot_header.asm
new file mode 100644
index 0000000..9a9289c
--- /dev/null
+++ b/src/arch/x86_64/multiboot_header.asm
@@ -0,0 +1,15 @@
+section .multiboot_header
+header_start:
+    dd 0xe85250d6                ; magic number (multiboot 2)
+    dd 0                         ; architecture 0 (protected mode i386)
+    dd header_end - header_start ; header length
+    ; checksum
+    dd 0x100000000 - (0xe85250d6 + 0 + (header_end - header_start))
+
+    ; insert optional multiboot tags here
+
+    ; required end tag
+    dw 0    ; type
+    dw 0    ; flags
+    dd 8    ; size
+header_end:
-- 
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