FizzBuzz OS
a project by mssola
Updated 7 months ago. 6 hacker ♥️. 5 followers.

Project Description

FizzBuzz OS (or just fbos) is an idea I've had in order to better grasp the fundamentals of the low level of a RISC-V machine. In practice, I'd like to build a small Operating System kernel that is able to launch three processes: one that simply prints "Fizz", another that prints "Buzz", and the third which prints "FizzBuzz". These processes are unaware of each other and it's up to the kernel to schedule them by using the timer interrupts as given on openSBI (fizz on % 3 seconds, buzz on % 5 seconds, and fizzbuzz on % 15 seconds).

This kernel provides just one system call, write, which allows any program to pass the string to be written into stdout.

This project is free software and you can find it here.

Goal for this Hackweek

  • Better understand the RISC-V SBI interface.
  • Better understand RISC-V in privileged mode.
  • Have fun.

Resources

Results

The project was a resounding success add-emoji Lots of learning, and the initial target was met.

Join this project

Looking for hackers with the skills:

assembly risc-v c kernel

This project is part of:

Hack Week 24

Activity

  • 7 months ago: cmatos left this project.
  • 7 months ago: fgonzalez joined this project.
  • 7 months ago: fgonzalez liked this project.
  • 8 months ago: cmatos joined this project.
  • 8 months ago: cmatos liked this project.
  • 8 months ago: rmarliere liked this project.
  • 8 months ago: jmodak liked this project.
  • 9 months ago: rmarliere joined this project.
  • 9 months ago: mbrugger liked this project.
  • 9 months ago: digitaltomm liked this project.
  • 10 months ago: mssola added keyword "assembly" to this project.
  • 10 months ago: mssola added keyword "risc-v" to this project.
  • 10 months ago: mssola added keyword "c" to this project.
  • 10 months ago: mssola added keyword "kernel" to this project.
  • 10 months ago: mssola started this project.
  • 10 months ago: mssola originated this project.


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    Goal for the Hackweeks

    1. Investigate if this is possible and the implications it would have (done in HW21)
    2. Hack up a PoC (done in HW22 and HW23)
    3. Prepare RFC series (giving it's only one week, we are entering wishful thinking territory here).

    update HW23

    • I was able to include the crash kernel into the kernel Image.
    • I'll need to find a way to load that from init/main.c:start_kernel() probably after kcsan_init()
    • I workaround for a smoke test was to hack kexec_file_load() systemcall which has two problems:
      1. My initramfs in the porduction kernel does not have a new enough kexec version, that's not a blocker but where the week ended
      2. As the crash kernel is part of init.data it will be already stale once I can call kexec_file_load() from user-space.

    The solution is probably to rewrite the POC so that the invocation can be done from init.text (that's my theory) but I'm not sure if I can reuse the kexec infrastructure in the kernel from there, which I rely on heavily.

    update HW24

    • Day1
      • rebased on v6.12 with no problems others then me breaking the config
      • setting up a new compilation and qemu/virtme env
      • getting desperate as nothing works that used to work
    • Day 2
      • getting to call the invocation of loading the early kernel from __init after kcsan_init()

    • Day 3

      • fix problem of memdup not being able to alloc so much memory... use 64K page sizes for now
      • code refactoring
      • I'm now able to load the crash kernel
      • When using virtme I can boot into the crash kernel, also it doesn't boot completely (major milestone!), crash in elfcorehdr_read_notes()

    • Day 4

      • crash systems crashes (no pun intended) in copy_old_mempage() link; will need to understand elfcorehdr...
      • call path vmcore_init() -> parse_crash_elf_headers() -> elfcorehdr_read() -> read_from_oldmem() -> copy_oldmem_page() -> copy_to_iter()

    • Day 5

      • hacking arch/arm64/kernel/crash_dump.c:copy_old_mempage() to see if crash system really starts. It does.
      • fun fact: retested with more reserved memory and with UEFI FW, host kernel crashes in init but directly starts the crash kernel, so it works (somehow) \o/

    • TODOs

      • fix elfcorehdr so that we actually can make use of all this...
      • test where in the boot __init() chain we can/should call kexec_early_dump()