stage0 VS mescc-tools-seed

Somewhat tangential, but I'm curious how big the bootstrap seed for Nix is. That is, if you wanted to build the entire world, what's a minimum set of binaries you'd need?

Guix has put quite a bit of work into this, AFAIU, and it's getting close to being bootstrappable all the way from stage0 [0]. Curious if some group is also working on similar things for Nix.

[0]:https://github.com/oriansj/stage0

https://www.bootstrappable.org/ has some good info. Reading the source of https://github.com/oriansj/stage0 is also very enlightening. It's set its goal to be understandable by 70% of programmers.

Even if they aren't, people absolutely should be able to bootstrap new platforms from scratch. It's important to have confidence in our tools, in our ability to rebuild from scratch, and to be safe against the "trusting trust" attack among other things.

Lately I've been catching up on the state of the art in bootstrapping. Check out the live-bootstrap project. stage0 starts with a seed "compiler" of a couple hundred bytes that basically turns hex codes into bytes while stripping comments. A series of such text files per architecture work their way up to a full macro assembler, which is then used to write a mostly architecture-independent minimal C compiler, which then builds a larger compiler written in this subset of C. This then bootstraps a Scheme in which a full C compiler (mescc) is written, which then builds TinyCC, which then builds GCC 4, which works its way up to modern GCC for C++... It's a fascinating read:

https://github.com/oriansj/stage0

https://github.com/fosslinux/live-bootstrap/blob/master/part...

Even if no one is "using" this it should still be a primary motivator for keeping C simple.

One countermeasure not mentioned here is bootstrapping a compiler with a program small enough to be manually verified. The stage0 project is under 1KB (small enough that the binary can be, and has been, manually checked against the hand written assembly), and GNU Guix (a system for reproducible, isolated builds) is currently working on moving it's bootstrap speed to stage0. That means that, fairly soon, there will be a large set of software that doesn't have a connection to an original C compiler.

From here I found a reference to the Gash, Mes-M2 and stage0 projects, who's README.org references a nice wiki for stage0. The Wiki references a more expansive stage0-posix repo. From here, I finally got all the pieces to fit togeather.

Of course, reproducible builds will only give you security if you trust the compiler you're using to verify. Unlike traditional distributions, Guix packages are rigorously defined in terms of their dependencies all the way down to ~60 MB of bootstrap binaries. There has been a lot of cool work to reduce the initial binary seed size, and they are working to reduce this even further to a "full source" bootstrap which will make use of the stage0 project to bootstrap the entire OS from a small, auditable ASCII Hex -> binary program.

stage0-posix just gained initial support for RISC-V (64-bit). It starts with 392 byte hex assembler, 361 byte "shell" and bootstraps simple linker (hex2), macro assembler (M0). Then it builds cc_riscv64 RISC-V compiler written in RISC-V assembly and uses it to build simple C compiler written in C (M2-Planet). Then it builds a few extra utilities (cp, mkdir, untar, ungz, sha256sum, chmod)

I wonder if Brainfuck could be used for https://github.com/oriansj/stage0-posix ? It would not surprise me if there is no other language for which there are so many interpreters written in so many different programming languages. It is even possible to write a Brainfuck interpreter in Brainfuck, which can be verified. And there is also a Brainfuck interpreter written in x86-64: https://github.com/316k/brainfuck-x86-64 . It is a little larger than hex0_x86.hex0 , but not too much to make it hard to verify.

I'd argue the easiest to implement language is macro-assembly then the C subset known as cc_x86

https://github.com/oriansj/mescc-tools-seed