Kernel Initialization

This document describes the detailed kernel initialization sequence in the Kyronix kernel. It is the child of Kernel Implementation Notes.

The kmain() function executes a nine-phase initialization sequence that brings up all kernel subsystems from early hardware detection through to the first userspace process execution.

Initialization Phases

1. Phase 1 — Early console and core tables: serial_init, printf setup, Global Descriptor Table (GDT) initialization (gdt_init), Interrupt Descriptor Table (IDT) initialization (idt_init), and keyboard initialization (kbd_init).

2. Phase 2 — Boot protocol validation: Validate Limine boot protocol responses, compute kernel_end_phys, and configure the bootstrap processor (BSP) Model-Specific Registers (MSRs) via g_cpu_local[0].

3. Phase 3 — Core memory and processor setup: Physical Memory Manager initialization (pmm_init), framebuffer initialization (fb_init), Virtual Memory Manager initialization (vmm_init), Local APIC (Advanced Programmable Interrupt Controller) initialization (lapic_init), Symmetric Multi-Processing initialization (smp_init), and Supervisor Mode Execution Prevention (SMEP) enable.

4. Phase 4 — Kernel services: Kernel heap initialization (heap_init), system call initialization (syscall_init), process subsystem initialization (proc_init), jail initialization (jail_init), Virtual File System initialization (vfs_init), and root mount verification.

5. Phase 5 — Hardware enumeration: PCI enumeration (pci_enumerate), Advanced Configuration and Power Interface (ACPI) initialization (acpi_init), block device initialization (block_init), AHCI (Advanced Host Controller Interface) initialization (ahci_init), VirtIO network initialization (virtnet_init), and network stack initialization (net_init).

6. Phase 6 — User interface devices: User Interface (UI) initialization (uio_init), framebuffer device initialization (fbdev_init), input subsystem initialization (input_init), virtual terminal initialization (vt_init), Programmable Interval Timer (PIT) initialization (pit_init), and LAPIC timer calibration (lapic_calibrate_timer).

7. Phase 7 — Application processor boot and entropy: BSP idle process creation, Application Processor (AP) boot (smp_boot_aps), and Cryptographically Secure Pseudo-Random Number Generator (CSPRNG) initialization with RDRAND instruction and Timestamp Counter (TSC) fallback.

8. Phase 8 — Interrupts and self-tests: sti (Set Interrupt Flag), PS/2 mouse initialization (ps2mouse_init), and self-tests for the PMM, VMM, and heap subsystems.

9. Phase 9 — Filesystem and init: ext2 filesystem initialization (ext2_init), root mount, initial ramdisk (initrd) load, Filesystem Table (fstab) mount, and execution of /init.

Self-Tests

The following self-tests execute during Phase 8 to verify core subsystem integrity.

PMM Self-Test

1. Allocate four physical pages.
2. Map each page to a virtual address via phys_to_virt.
3. Write the constant 0xDEADBEEFCAFEBABE to each page.
4. Verify that each page contains a unique allocation (distinct physical addresses).

VMM Self-Test

1. Map a single page at virtual address 0xffff900000001000.
2. Write the constant 0xC0FFEE00DEADC0DE to the mapped page.
3. Read back and verify the written value.
4. Unmap the page.

Heap Self-Test

1. Allocate buffers of 64, 128, and 256 bytes.
2. Fill the 64-byte buffer with 0xAA, the 128-byte buffer with 0xBB, and the 256-byte buffer with 0xCC.
3. Verify each buffer contains the expected fill pattern.
4. Test krealloc by reallocating each buffer and verifying content preservation.

Last reviewed: 2026-07-22