Update on the Mu computer

Now that we have a bootstrapped (quasi-) language and (kinda) bootstrapped OS, we're finally starting to think about less error-prone notations.

This week two of us built a notation for x86 addressing modes:

• direct: %ecx
• indirect: *ecx
• indirect with displacement: *(ecx+4)
• indirect with index, scale and displacement: *(ecx + edx<<3 + 4)

Not yet sure this is a good approach. But it'll be fun to playtest.

Here's before and after screenshots for factorial.subx.

Before:

After:

(project link)

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Now that I have the beginnings of a whole new computer, I'm at a loss for what to work on next. (One of the items is H's suggestion of socket syscalls.)

Today's little mini-experiment: a program to print out random numbers in an infinite loop. Works fine on Linux or Mac, but only prints zeroes when packaged up with my kernel fork and run on Qemu or Linode. Looks like I need to do something to initialize /dev/random.

(More details)

Here's my complete current list of ideas, just for triggering serendipity:

• Test /dev/random without my kernel changes
• Test framebuffer syscalls
• Client socket helpers
• A compiled language -- kinda like my previous prototype (https://github.com/akkartik/mu1#readme)
• Some sort of storage. Either ramdisk (volatile) or local disk (needs mount) or S3 (needs sockets)
• An interpreted language. Either a subset of Oil or a straight-up Lisp. Needs storage.

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Updated Mu's fork of the Linux kernel again. Today I deleted the entire top-level sound/ directory and a whole bunch of unused file systems.

LoC down from 6.1M to 4.4M.

Context: https://github.com/akkartik/mu#readme

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Stack manipulations in SubX

I've been noodling on a Forth-inspired (but likely insane) syntactic sugar for stack manipulations in raw machine code. Behold:

{ 0 0 ->%ecx
...
}

This expands to:

push 0/imm32
push 0/imm32
copy %esp to %ecx
...
add 8 to %esp

Basically you get a (fairly unsafe) block scope containing an 8-byte local in %ecx.

To temporarily spill a register:

{ %ecx
...
}

Function call:

{ z y x
call f/disp32
}

The `}` turns into code to undo pushes in the `{` line.

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Now that I'm packaging Mu with a fork of bleeding-edge Linux, I have a tiger by the tail. I need to stay abreast of changes from upstream or risk bitrot, particularly as new security vulnerabilities are uncovered and patched.

I'm going to start changing the kernel soon, and I need a way to not kill myself merging patches from upstream. For starters: aggressively delete code Mu doesn't need. That'll reduce merge conflicts.

In the first run I just deleted non-x86 architectures. So far so good.

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Turn a set of .subx files into a bootable disk image.

$ git clone https://github.com/akkartik/mu
$ cd mu
# package up a "hello world" binary and Linux kernel into mu.iso
$ ./gen_iso examples/ex6.subx
# try it out
$ qemu-system-x86_64 -m 256M -cdrom mu.iso -boot d

https://github.com/akkartik/mu#readme

The process is still fairly klunky, and I've added several large dependencies. But now that I have something working I can start polishing it.

Credit: http://minimal.linux-bg.org/

One aspect that seems more broadly useful than just my own Assembly language project: how to deploy bootable disk images on Linode.

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Cloud VPS from "scratch"

I just successfully built a minimal Linux kernel, installed a SubX binary as init -- and ran the whole thing on a Linode.

It's not in https://github.com/akkartik/mu yet, but there will soon be step-by-step instructions.

This couldn't have happened without the education I received from http://minimal.linux-bg.org

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Table literals in my Assembly language

https://github.com/akkartik/mu/blob/37c859058/apps/desugar.subx#L440

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Question for Unix experts: why do we need open()?

I've spent some time in the past staring at the abyss that is http://pubs.opengroup.org/onlinepubs/009695399/functions/open.html, and much of its complexity seems needed only for Things That Are Not Files.

At the syscall level it's pretty ugly that sockets are not files. Alternative client-side syscalls that unify file system and network:

• PUT
• GET
• POST
• DELETE

Just have them take a resource name and maybe a Go channel for synchronizing. What am I missing?!

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My new Assembly syntax

SubX can now build itself! 9kLoC in 1.5s. Caveats:

1. Zero error checking. You still need the C++ translator for development (just like a text editor and other tools).
2. Some programs compile with the C++ translator but not the self-hosted one. Ones with no `Entry` labels, no `data` segments, or with uppercase hex will throw errors. However, it's a bug if a program successfully compiles but generates a different binary.

What's next? I have a few ideas.

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