Makar

A bare-metal i686 hobby OS written in straight C (no C++, no managed runtime), booted via GRUB Multiboot 2. Targets 32-bit protected mode, ships in QEMU, runs on real hardware once installed to disk.

Sibling of Medli — the C# / Cosmos counterpart. The two share a command vocabulary, filesystem layout, and long-term binary-format goals while exploring how language choice shapes the implementation.

Current version: 0.9.0 (kernel self-host milestone; see include/kernel/version.h and kernel rebuild guide).

What works today

Subsystem State
Boot GRUB Multiboot 2, 5 s menu (Makar OS / chainload next device). Cmdline parsed for test_mode + console=ttyS0.
Display VESA framebuffer (Bochs VBE, 720p default); VGA 80×50 fallback. vesa_pane_t pane abstraction.
Multi-TTY 4 preemptive shell tasks shell0–shell3, Alt+F1–F4 to switch. Per-TTY vt_buf_t backing grid; FB painted only when focused; makmux multiplexer’s status bar at the bottom row (left label, centred VT1 VT2 VT3 VT4, Alt+F1-F4 hint; Alt+F5 toggles the label between Makar and a live HH:MM:SS DD/MM/YY clock). Framebuffer syscalls are focus-gated so a backgrounded fullscreen app stays isolated to its VT.
VIX editor vim-style line-number gutter, word wrap, flashing block caret (SYS_CARET_STYLE), status row, runtime-resolution agnostic. Now a userland ELF (vix.elf) run via PATH — appears in maktop as its own task. Renamed from VICS during the port — see Makar × Medli.
Storage FAT32 + ext2 (HDD/USB) + ISO 9660 (CD-ROM) over IDE PIO, routed via a real VFS mount table (s_mounts[] in vfs.c; longest-prefix-match dispatch). Rootfs election (vfs_mount_root) honours root=/dev/hdaN Multiboot2 cmdline first, else auto-detects (ext2 → FAT32 → CD-ROM emergency) by probing each candidate for /usr/lib/crt0.o. Single-partition disks auto-mount at /mnt/root; dual-partition installer layouts bind partition 0 at /mnt/boot (also mirrored at /boot) and partition 1 at /mnt/root; CD-ROM at /mnt/cdrom. Synthetic overlays (/dev /proc /tmp /log) are first-class mount-table entries. mount /dev/hdaN /mnt/<name> auto-detects the backend (ext2 superblock else FAT32). FAT32 and ext2 mount simultaneously at separate mountpoints (one of each — the drivers are single-volume). Read + write + delete + rename + mkdir on both; mkfs.fat32 / mkfs.ext2 to format; flush + unmount on shutdown/reboot. /root mkdir’d best-effort on writable rootfs boots.
/dev Synthetic block-device tree: /dev/hda[N] (ATA disks + partitions), /dev/cdrom (ATAPI). Byte-addressed read/write over native sector I/O; backs fdisk.elf / cfdisk.elf and mount.
/proc Synthetic filesystem with cpuinfo, meminfo, tasks, uname, rtc — content generated on each read. meminfo MemUsed folds in heap; tasks has a per-task MEMKB column.
Memory PMM bitmap allocator, paging (256 MiB identity + per-task 4 KiB user pages), kernel heap.
Tasking Preemptive round-robin scheduler. PIT 100 Hz, SCHED_QUANTUM = 4 ticks (40 ms slice). Per-task pid, parent_pid, cwd, tty, real fd_table_t, signal bitmasks, exit_status. User PD reaped on task exit. Lifecycle: READY → RUNNING → ZOMBIE → DEAD.
Processes Full POSIX fork + execve + wait4: copy-on-write page-table clone (per-frame refcounts + VMM_PTE_COW software bit + COW #PF handler with CR0.WP enforced), execve replaces caller’s address space with a new ELF, wait4 reaps zombies and round-trips the child’s exit_status.
Userspace Ring-3 via iret. ELF loader (elf_exec) with argc/argv. Apps: hello, calc, vix, diskinfo, fdisk, cfdisk (full-screen cfdisk-style MBR editor), basic (C64-style integer BASIC w/ graphics), kbtester, makbox (multicall: ls/cat/cp/mv/rm/rmdir/echo/pwd), clock, lines, maktop, sigtest, forktest + execvetest.
Syscalls Linux i386 ABI subset over int 0x80 (1 exit, 2 fork, 11 execve, 19 lseek, 37 kill, 45 brk, 48 signal, 114 wait4, 119 sigreturn, 158 yield, …) + Makar extensions (200–218; 218 = SYS_CARET_STYLE). /dev nodes open as FD_KIND_BLOCKDEV so read/write/lseek do sector I/O.
Shell Inline editing, 16-entry history, cross-FS tab completion, glob expansion, Ctrl+C sigint, lsman/man <cmd>, settable PATH variable. Fullscreen-command dispatch with auto FB restore.
Drivers 16550 UART, PIT, layered PS/2 keyboard (full set-1 + e0 with per-task SPSC rings), ATA/IDE PIO 28-bit LBA, MBR + GPT partition tables.
Debug INT 1 / INT 3 GDB-friendly handlers, kernel panic screen, ktest harness with per-suite descriptions and VGA + serial output.
Serial Linux-style: dmesg + explicit diagnostics by default. console=ttyS0 cmdline or verbose [on\|off] shell builtin opts into TTY-mirroring.

Minimum system requirements

Makar targets emulation (QEMU) but is designed to run on period-appropriate real hardware once installed to disk.

Resource Minimum Recommended
CPU i686 (Pentium Pro / 1995) — 32-bit protected mode, PSE large pages Any i686+; runs in QEMU TCG without KVM
RAM 32 MiB (CI/test config boots with qemu -m 32; ~29 MiB free after the PMM reserves the kernel) 256 MiB (kernel identity-maps the low 256 MiB)
Firmware BIOS with GRUB Multiboot 2 (the boot device tag is read for auto-mount; root=/dev/hdaN on the kernel cmdline picks the rootfs explicitly) —
Display VGA text 80×50 (always works) Bochs VBE for the 720p VESA framebuffer (qemu -vga std)
Storage None required to boot (live shell). For persistence: an ATA/IDE disk (PIO, 28-bit LBA) with an MBR or GPT FAT32 partition; optional ext2 partition ATA HDD with FAT32 boot + ext2 data partitions (auto-mount at /mnt/boot + /mnt/root; rootfs election lifts the latter to /)
Input PS/2 keyboard (set-1 + 0xE0 extended) —
Boot media ISO 9660 CD-ROM (-cdrom makar.iso) or a FAT32 HDD image with GRUB —

USB HID keyboards, networking, and x86-64 are not yet supported (see the roadmap).

Kernel subsystem reference

Per-driver and per-module documentation:

Document Description
kernel Boot entry point and post-boot heartbeat
system Panic, halt, and assertion helpers
asm Inline x86 port I/O and CPU-control helpers
types Common type aliases and geometric structs
vga VGA text-mode constants and low-level helpers
tty VGA text terminal driver
serial Serial port (UART) driver
descr_tbl GDT and IDT initialisation
isr Interrupt and IRQ dispatch
timer PIT timer driver and ksleep
pmm Physical memory manager
paging Paging and virtual memory
heap Kernel heap allocator (kmalloc / kfree)
vesa VESA linear framebuffer driver
vesa_tty VESA bitmap-font text renderer
vt Per-TTY logical character grid (Linux vc_data-style backing buffer)
vtty Virtual TTY manager (focus, Alt+Fn switch, deferred repaint, status bar)
debug INT 1 / INT 3 debug-exception handlers
multiboot Multiboot 2 structure definitions
keyboard PS/2 keyboard driver (layered, IRQ 1, set 1 + e0, per-task SPSC rings)
ide ATA/IDE PIO driver (28-bit LBA read/write)
partition MBR and GPT partition table driver
ext2 ext2 filesystem driver (read + write + mkfs)
procfs Synthetic /proc filesystem
devfs Synthetic /dev block devices (disks, partitions, CD-ROM)
shell Interactive multi-TTY kernel command shell

Standard library

Document Description
libc overview Freestanding libc (libk.a)
stdio printf, putchar, puts
stdlib abort
string Memory and string utilities

Source map 

src/kernel/arch/i386/
  boot/       Multiboot 2 entry, crti/crtn
  core/       GDT/IDT, ISR stub, interrupt dispatch
  mm/         pmm.c, paging.c, vmm.c, heap.c
  drivers/    serial, keyboard, timer, IDE, ACPI, partition
  fs/         fat32.c, ext2.c, iso9660.c, procfs.c, devfs.c, vfs.c
  display/    tty.c, vesa.c + vesa_tty.c, vt.c
  proc/       task.c + task_asm.S, syscall.c, ring3.S, vtty.c
  shell/      shell.c, shell_cmd_*.c
  debug/      exception handlers
src/kernel/kernel/kernel.c    kernel_main
src/kernel/include/kernel/    public headers
src/libc/                     freestanding libc → libk.a
src/userspace/                ring-3 ELF apps
tests/                        gdb_boot_test.py, ui_test.sh

Acknowledgements

Makar draws on the work of many FOSS projects. Full attribution in LICENSES/THANKS.md and per-file source-level credits. Key influences:

  • Linux kernel (GPLv2) — syscall ABI, ELF loading model, process memory layout
  • ELKS / FUZIX (GPLv2) — minimal-libc / crt0 approach; vi-style editor design
  • CP/M — terminal-owns-screen philosophy; self-contained program model
  • musl libc (MIT) — target libc for the userspace porting roadmap
  • GRUB (GPLv2) — bootloader and Multiboot 2 tag format
  • OSDev wiki (CC-BY-SA) — cross-compiler setup, paging, descriptor tables