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boot/readme.md

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Overview

Currently we boot from BIOS on a GPT-partitioned disk.

boot0.s is the first-stage bootloader. It lives in the MBR bootstrap field, and must therefore fit into 440 bytes. Its tasks are:

  • Set up a stack etc.
  • Get the boot drive geometry
  • Load and parse the GPT
  • Find the partition of the second stage
  • Load and jump to the first sector of the second stage

boot1.s is the second-stage bootloader. Its tasks are:

  • Load its own sectors not loaded by the first stage
  • Enable A20
  • Detect available memory
  • Enter unreal mode
  • Read the kernel ELF from disk (don't have to parse the ELF just yet)
  • Get all the useful information we can from the BIOS before we leave unreal mode
  • Enter long mode (possibly via protected mode?)
  • Load the kernel ELF
  • Initialise stack etc. for the kernel
  • Jump to kernel