mboot

mboot is a minimal os for i386 platforms.

Prequisites

Building mboot depends on:

• llvm tools (clang, ld.lld)
• nasm

Running mboot needs:

• the building tools or a disk image
• qemu-system-x86_64

Building

make
# normal os
qemu-system-x86_64 -m 4G -drive file=image.img -serial stdio

# with networking enabled
qemu-system-x86_64 -m 4G -drive file=image.img -serial stdio -device e1000,netdev=n0 -netdev user,id=n0 -object filter-dump,id=f1,netdev=n0,file=netdump.pcap

# with networking enabled and UDP forwarded from host port 10007 to guest port 7
qemu-system-x86_64 -m 4G -drive file=image.img -serial stdio \
  -device e1000,netdev=n0 \
  -netdev user,id=n0,hostfwd=udp::10007-:7 \
  -object filter-dump,id=f1,netdev=n0,file=netdump.pcap

UDP demo

The kernel brings up the network interface at boot (stage2/net/net.c): guest IP 10.0.2.15/24 with gateway 10.0.2.2. The init system (user/src/init.c) assigns each process a tty at spawn: init stays on tty1, the Lua interpreter runs on tty4, the UDP echo service on tty2, and ping (user/src/ping.c, a raw ICMP socket via socket(AF_INET, SOCK_RAW, IPPROTO_ICMP)) on tty3. Processes cannot rebind their stdio to a different tty — the kernel rejects dup2 of another tty onto stdin/stdout/stderr.

Run QEMU with host UDP forwarding:

qemu-system-x86_64 -m 4G -drive file=image.img -serial stdio \
  -device e1000,netdev=n0 \
  -netdev user,id=n0,hostfwd=udp::10007-:7 \
  -object filter-dump,id=f1,netdev=n0,file=netdump.pcap

From the host, send a datagram to the forwarded port:

printf 'hello from host\n' | nc -u -w 1 127.0.0.1 10007

If your nc supports listen mode, you can also watch the echoed reply with a second terminal:

nc -u -l 10007

On the guest serial log you should see:

• NET: and IPV4: messages for the kernel-side interface bring-up
• ping: messages for the raw-socket ICMP echo round trips
• an RX a.b.c.d:src -> 10.0.2.15:7 log line for the UDP datagram

todo:

• 32 bit protected mode
• cpu exceptions
• individual hardware interrupts
• a ps/2 keyboard
• vga driver
• reading ata drives
• rs232 interface
• the intel 8259 PIC
• the intel 8253 PIT
• the mbr partitioning scheme
• fat 16 as the filesystem
• enable x87 fpu
• memory allocator
• elf loader
• paging
• libc
• implement more demos to show syscalls working

Features

Screenshots

Oct 20, 2025:

Aug 6, 2026: