[fjfaase]

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.

[kragen]

Bootfuckbrainstrapping (?) is definitely an interesting idea; I explored it in some depth in https://dercuano.github.io/notes/uvc-archiving.html#addtoc_2 and https://dercuano.github.io/notes/self-compiler-bootstrapping..., and I concluded that although BF is inspiring, it would be easy to do better. Also, although the interpreter you point at compiles to 11331 bytes on my machine (5992 stripped, 5912 after objcopy -S -R .note.gnu.build-id bf bf.small) Brian Raiter wrote a 199-byte BF interpreter for i386 Linux last millennium: http://www.muppetlabs.com/~breadbox/software/tiny/bf.asm.txt

[fjfaase]

I have written a BrainFuck generator for writing a BrainFuck program which could replace the hex0 seeds. See https://www.iwriteiam.nl/BFgen.html

[kragen]

This is pretty cool!

The dataflow is not totally clear to me—am I understanding correctly that the parser generator is implemented by a recursive-descent parser implemented in 1400 lines of JS, which then compiles the example grammar in "grammar" into the top-down Forthish code in "grammar_error", which is then used to compile the Algolish code in "input" into the Lispish code in "output", which is then compiled into the BF in "result"?

While this is an inspiring and aesthetically delightful achievement, it's not clear that it helps with the hex0 seeds, because executing the 1400-line recursive-descent parser requires the seed to grow by the size of one JavaScript execution engine; all the existing ones are about four orders of magnitude larger than the live-bootstrap seed. Lacking that, a malicious JS execution engine could inject malicious code into the BF output, in the Karger–Thompson-attack scenario.

I suspect that the initial grammar compilation could be achieved by a cut-down compiler-compiler along the lines of what I'm working on in http://canonical.org/~kragen/sw/dev3/meta5ix.m5, although Meta5ix itself is not currently bootstrappable from a human-written seed.

[fjfaase]

Thanks!

It is not so much a parser generator as in interpreting parser. It is based on https://fransfaase.github.io/ParserWorkshop/Online_inter_par... which I developed earlier this year.

My idea was not to use the input as the base of the seed, but the generated BrainFuck program. The idea is that there are a multitude of BrainFuck interpreters/compilers in a multitude of programming languages that one could use verify that they are not malicious.

Also, I think it is easier to verify that a BrainFuck program is not malicious than a program in machine code. The x86 instruction set is rather large, I understand, with all its extensions. I understand that only a very restricted subset of instructions is used in the seed, but one still needs to verify this requiring to understand the x86 instruction documentation. Verifying the BrainFuck program is not easy, but it does not require the access to some external document. Besides the definition of the language, only an ASCII table, which would also be needed for x86 seed, BTW.

[NieDzejkob]

Except that brainfuck was actively designed to make programming difficult, and as you can only increment and decrement, the performance is abysmal.

[fjfaase]

The performance argument is not a real issue if it is only used as a replacement for sed/xxd combination. And yes, it was designed to make programming difficult, but one could argue that it is easier to verify manually than machine code, because machine code requires you to know the whole x86 instruction set, which I understand, is rather large, taking into account all the extensions. I suspect that these exentions are not used in the stage0 code, but we still have to verify that they are not used.

[kragen]

You can make more efficient BF interpreters and compilers that recognize common patterns and optimize them.