TwoKernel

A hobbyist monolithic kernel written in c++. Trying to be posix style.

Resources

Limine-c++-template: https://codeberg.org/Limine/limine-cxx-template/src/branch/trunk/limine.conf

Roadmap

Completed

01 — Boot & C++ runtime

• Limine config + base revision check
• C++ global constructor invocation
• hcf halt routine
• Linker script

02 — Output & logging

• Framebuffer driver
• Flanterm-backed TTY
• klog printf-style kernel logger
• Minimal libc (memset/memcpy/strlen, etc.)

03 — CPU descriptors & interrupts

• GDT load
• IDT + ISR stubs
• Exception handlers
• PIC remap + IRQ mask scaffolding

04 — Memory

• PMM with free-list allocator
• VMM: 4-level paging, kernel HHDM mapping, kernel section mapping with NX, EFER.NX, CR3 load
• Reclaim bootloader_reclaimable memory after VMM init (stub exists, not wired into kmain)

05 — Scheduling

• Thread/Task struct (registers, kernel stack, state)
• Context switch in asm (save/restore GPRs, RFLAGS, RIP, RSP)
• Ready queue + round-robin scheduler
• Timer-driven preemption (PIC timer ISR → schedule())
• sleep/wait queues, blocking primitives
• Idle thread

06 — Userspace

• User CS/DS/TSS in GDT, IST stacks
• Per-process address space (clone kernel-half PML4 entries into new pagemap)
• User page mapping flags (USER bit) in VMM
• ELF64 loader (program headers → mmap into address space)
• iretq-based ring 3 entry
• Syscall entry: SYSCALL/SYSRET, MSR setup (STAR/LSTAR/SFMASK)
• Initial syscall set (write, exit, getpid, mmap, brk)
• Kernel heap (kmalloc/kfree, slab or bump-then-free-list on top of PMM)
• unmap should also free intermediate page tables when empty + INVLPG / TLB shootdown
• Replace PIC with APIC + LAPIC timer (or HPET) — needed for preemptive scheduling
• ACPI table parsing (RSDP/MADT) — feeds APIC/SMP
• PS/2 keyboard or serial input for interactive debugging

07 — IPC

• Pipes or message ports
• Shared memory regions (VMM API for shared mappings)
• Signals or equivalent async notification
• Synchronization primitives exposed to userspace (futex-like)

08 — Virtual File System

• VFS node abstraction (vnode/inode, ops table)
• Mountpoint + path resolution
• In-memory tmpfs as first backend
• File descriptor table per process
• open/read/write/close/stat syscalls
• A real disk FS (FAT32 or ext2) and a block driver (AHCI/virtio-blk) when ready