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Boot Flow

Sinux boots through GRUB 2 using the Multiboot2 protocol, transitions from 32-bit protected mode to 64-bit long mode, and finally jumps into the C entry point kernel_main().

BIOS/UEFI → GRUB 2 → Multiboot2
  → boot.asm (32-bit)
      ├── Validate Multiboot2 magic
      ├── Check CPUID + Long Mode support
      ├── Build PML4/PDPT/PDT page tables (identity map first 1 GiB)
      ├── Enable PAE + LME + Paging
      ├── Load 64-bit GDT
      └── Jump to kernel_main() (64-bit C)

Stages explained​

  1. Firmware (BIOS/UEFI) loads GRUB. Secure Boot must be OFF.
  2. GRUB 2 loads the kernel using the Multiboot2 specification and passes a boot information structure.
  3. boot.asm runs in 32-bit mode and:
    • Validates the Multiboot2 magic value.
    • Uses CPUID to confirm Long Mode (64-bit) support.
    • Builds page tables (PML4 → PDPT → PDT) that identity-map the first 1 GiB.
    • Enables PAE, the LME bit, and paging.
    • Loads the 64-bit GDT.
    • Far-jumps into 64-bit kernel_main().

From there, the C kernel initializes the memory managers, drivers, filesystem, and scheduler before dropping into the built-in shell.