xv6-public VS Mezzano

+1 for mini operating system.

Us, application developers, rely on many OS features: memory management, filesystem, etc. I'm sure eventually we'll ask "how such things are done behind the scene?"

That's why I tinker with xv6 (https://github.com/mit-pdos/xv6-public) during sparetime. Learning various process scheduling algorithms from textbook is a thing. Implementing it is another thing. I learn a lot. And it's definitely fun, even though there's almost zero chance the knowledge gained is relevant for my job (I'm a mobile app dev).

Recently I compiled xv6 using gcc 7.5.0 on Ubuntu 18 , everything is ok. But when I try to compile it using gcc 13.2.1 on latest Arch, it's failed: result

https://github.com/mit-pdos/xv6-public has under 10,000 lines of C and assembly including some user space programs.

xv6 was originally written for 32-bit x86; the RISC-V port is a relatively recent development. See e.g. https://github.com/mit-pdos/xv6-public for some of the earlier history.

rxv64 was written for a specific purpose: we had to ramp up professional engineers on both 64-bit x86_64 and kernel development in Rust; we were pointing them to the MIT materials, which at the time still focused on x86, but they were getting tripped up 32-bit-isms and the original PC peripherals (e.g., accessing the IDE disk via programmed IO). Interestingly, the non sequitur about C++ aside, porting to Rust exposed several bugs or omissions in the C original; fixes were contributed back to MIT and applied to the original (and survived into the RISC-V port).

Oh, by the way, the use of the term "SMP" predates Intel's usage by decades.

I'd define an arena as the pattern where the arena itself owns N objects. So you free the arena to free all objects.

My first job was at EA working on console games (PS2, GameCube, XBox, no OS or virtual memory on any of them), and while at the time I was too junior to touch the memory allocators themselves, we were definitely not malloc-ing and freeing all the time.

It was more like you load data for the level in one stage, which creates a ton of data structures, and then you enter a loop to draw every frame quickly. There were many global variables.

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Wikipedia calls it a region, zone, arena, area, or memory context, and that seems about right:

https://en.wikipedia.org/wiki/Region-based_memory_management

It describes history from 1967 (before C was invented!) and has some good examples from Apache ("pools") and Postgres ("memory contexts").

I also just looked at these codebases:

https://github.com/mit-pdos/xv6-public (based on code from the 70's)

https://github.com/id-Software/DOOM (1997)

I looked at allocproc() in xv6, and gives you an object from a fixed global array. A lot of C code in the 80's and 90's was essentially "kernel code" in that it didn't have an OS underneath it. Embedded systems didn't run on full-fledges OSes.

DOOM tends to use a lot of what I would call "pools" -- arrays of objects of a fixed size, and that's basically what I remember from EA.

Though in g_game.c, there is definitely an arena of size 0x20000 called "demobuffer". It's used with a bump allocator.

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So I'd say

- malloc / free of individual objects was NEVER what C code looked like (aside from toy code in college)

- arena allocators were used, but global vars and pools are also very common.

- arenas are more or less wash for memory safety. they help you in some ways, but hurt you in others.

The reason C programmers don't malloc/free all the time is for speed, not memory safety. Arenas are still unsafe.

When you free an arena, you have no guarantee there's nothing that points to it anymore.

Also, something that shouldn't be underestimated is that arena allocators break tools like ASAN, which use the malloc() free() interface. This was underscored to me by writing a garbage collector -- the custom allocator "broke" ASAN, and that was actually a problem:

https://www.oilshell.org/blog/2023/01/garbage-collector.html

If you want memory safety in your C code, you should be using ASAN (dynamically instrumented allocators) and good test coverage. Arenas don't help -- they can actually hurt. An arena is a trivial idea -- the problem is more if that usage pattern actually matches your application, and apps evolve over time.

Magma is proudly licensed under the MIT license, and uses code from Xv6 and Yagura.

My OS classes used xv6, a reimplementation of Unix Version 6 for a RISC-V architecture. Accompanying that was the OSTEP textbook.

Check out xv6 if you are only getting started with operating systems and want something simpler.

Here is kernel.ld.

Have you made or plan to make any contributions to Mezzano (https://github.com/froggey/Mezzano) or are you mainly interested in seeing how far you can take this thing on your own?

>> except building compilers and OSes

SBCL is written in Lisp, yes? Except the runtime, which is C + asm.

I've heard people wrote some OSes in the past, like Genera. Or if you prefer recent attempt, try https://github.com/froggey/Mezzano. Never tried it, though.

No need to.

Not at all. See mezzano for a notable recent example of an OS written entirely in a dynamic language.

So..

"Why do you want to make Lisp more popular? If you were sucessful, what would be different in the world, and why is that desirable to you?"

Normally at this point I'd listen to the response, and ask more questions based on that. That would wind up with a very, very deep thread, so I'll break a cardinal rule and pre-guess at some answers.

This kind of question comes up pretty frequently. In many cases, I suspect the motivation behind the question is "Wow! Here's this cool tool I've discovered. I want to make something really useful with it. I want to do it as part of a community effort; share my excitement with others, share in their excitement, and know that what I'm making is useful because others find it desirable and are excited by it." The field could be cooking, sports, old machine tools, tiny homes, or demo scene. Its the fundemental driver for most content on HN, YouTube, Instructables, and such. It is a Good Thing.

If that is your motivator, then my suggestion is to find something that bugs you and fix it. You've already decided you're only interested in code, not other aspects. You said you preferred vim, but the emacs ecosystem has a very rich set of sharp edges that need filing off, and a rich set of tools with which to attack them.

One example: even after 50 years there's no open IDE which allows you to easily globally rename a Lisp identifier. I don't know about LispWorks or other proprietary environments, but you can't in emacs or vim do a right-click on "foo" in "(defun foo ()...)" and select a command which automatically renames it in all invocations. [Queue lots of "but you can..." replies here.] I don't think vim is up to the task of doing this internally. It would be possible in emacs; but would require a huge effort with lots of help from other people. If you emerged alive from that rabbit warren you'd join the company of Certified "How Hard Could it Be?" Mad Scientists such as Dr. "I just want to draw molecules" Meister [1] and "Wouldn't an OS in Lisp be Cool" Froggey [2].

[1] https://github.com/clasp-developers/clasp

[2] Mezzano https://github.com/froggey/Mezzano

You might want to look at Mezzano which is an operation system written in Common Lisp https://github.com/froggey/Mezzano

I haven’t tried it since moving to M1/ARM, but it is cool.