Booting

The Boot Process §

• Executes Motherboard ROM firmware code
  1. power-on-self-test(https://en.wikipedia.org/wiki/Power-on_self-test)
  2. detect available RAM
  3. pre-initialize CPU & other hardwares
  4. looks for bootable disk

Patch for bootloader_api crate §

bootloader_api를 이용하려 하였으나, x86 dependent한 요소가 많아 더 이상 이용하지 않음

• Translate instruction from x86 to aarch64
• Reference
  • https://developer.arm.com/documentation/dui0068/b/ARM-Instruction-Reference/ARM-general-data-processing-instructions/ADD—SUB—RSB—ADC—SBC—and-RSC
  • https://c9x.me/x86/html/file_module_x86_id_5.html

Bootable Disk Image §

• Update: abandon creating disk image since our os will boot on uefi-app
• Update: abandon uefi since there were some compatibility issue when using asm

mkdir kernel
mv src kernel/
mv Cargo.toml kernel/
cargo init --new cosmos

# top-level Cargo.toml
[workspace]
members = ["kernel"]

UEFI APP §

rustup install nightly

# rust-toolchain.toml
[toolchain]
channel = "nightly"

rustup target add aarch64-unknown-uefi
cargo build --target aarch64-unknown-uefi

BIOS vs UEFI §

BIOS §

Basic Input Output System

• Stored in EPROM (Erasable Programmable Read Only Memory)
• Uses MBR Partitioning Scheme
• Legacy Way
• Requires 16bit-32bit-64bit transition since it starts on 16bit mode

UEFI §

Unified Extensible Firmware Interface

• Requires EFI System Partition (ESP) to store .efi file
• .efi file includes all device initialization & startup codes.. (could be kernel itself)
• Uses GPT Partitioning scheme

Reference §

• phil-opp/blog-os: https://github.com/phil-opp/blog_os/blob/edition-3/blog/content/edition-3/posts/02-booting/index.md
• UEFI vs BIOS: https://phoenixnap.com/kb/uefi-vs-bios