Architecture

Architecture

NyxOS is a monolithic kernel with loadable modules, running in long mode (x86_64) with 4-level paging.

See also: Boot Process, Memory Management, Process Management, Networking Stack, GUI Subsystem, Filesystem, Drivers, Syscalls, SMP, Security

Overview

+--------------------------------------------------------+
|                    Userspace (Ring 3)                   |
|  sh.elf  init.elf  top.elf  edit.elf  ps.elf  kill.elf |
|  cat/wc/ls/find/sort/grep/head/tail/mkdir/rm/touch     |
+--------------------------------------------------------+
|              System Call Interface (syscall/sysret)     |
+--------------------------------------------------------+
|                    Kernel (Ring 0)                      |
|  +----------+ +---------+ +--------+ +-----------+     |
|  | Scheduler | | Memory  | | VFS    | | Networking |   |
|  |  + IPC    | | Manager | | + EXT2 | | TCP/IP     |   |
|  +----------+ +---------+ +--------+ +-----------+     |
|  +---------+ +--------+ +---------+ +-----------+      |
|  | Drivers | | GUI    | | ELF     | | Initramfs |      |
|  |(kbd,mouse| | Compo- | | Loader  | |           |     |
|  | SB16,    | | sitor  | |         | |           |     |
|  | RTL8139) | |        | |         | |           |     |
|  +---------+ +--------+ +---------+ +-----------+      |
+--------------------------------------------------------+
|                 Hardware Abstraction Layer              |
+--------------------------------------------------------+
|                      x86_64 Hardware                    |
|  CPU  | APIC | I/O APIC | PIT | PCI | ATA | VBE | PS2 |
+--------------------------------------------------------+

Kernel structure

All kernel source lives in kernel/. Key files:

File	Purpose
kernel.c	Main entry, shell, command handlers
kernel.h	Typedefs, constants, extern declarations
boot.asm	Multiboot header, GDT, long mode entry
memory.c	Bitmap physical page allocator
heap.c	16 MB kernel heap (kmalloc/kfree)
paging.c	4-level paging, demand paging, COW
process.c	Process table, scheduler, background tasks
switch.asm	Context switch assembly
vfs.c	Ramdisk VFS + mount table
ext2.c	EXT2 filesystem driver
compositor.c	Window compositor (32 windows, z-order)
tcp.c	Full TCP state machine
elf.c	ELF64 loader
apic.c	Local APIC + I/O APIC
smp.c	Multi-core bringup
rtl8139.c	RTL8139 NIC driver

Higher-half kernel

The kernel is mapped at the higher half using PML4[511] (the last entry). The user half occupies PML4[0..510]. The kernel page tables mirror the identity mapping (low 64 MB of physical memory accessible through the higher-half alias). This provides page-table isolation: user page directories lack the identity mapping, so a user process cannot access kernel memory.

Key constants

• KERNEL_BASE = 0xFFFF800000000000
• KERNEL_HEAP_SIZE = 16 MB
• MAX_PROCESSES = 64
• PAGE_SIZE = 4096
• MAX_CPUS = 8