RustHaruspex big-lip-bob

This is the translation of my blog posts. You can find them here (in Russian).

Exploiting Lua 5.1 on x86_64

The following Lua program generates a Lua bytecode program called lua-sandbox-rce.luac, which in turn spawns a shell from within Lua 5.1 sandbox. The remainder of this document attempts to explain how this program works by a whirlwind tour of relevent bits of the Lua 5.1 virtual machine.

function outer()
  local magic -- In bytecode, the stack slot corresponding to this local is changed
  local function middle()
    local co, upval
    local ub1 = {[0] = -- Convert uint8_t to char[1]

I think I’ve figured out most parts of the cubical type theory papers; I’m going to take a shot to explain it informally in the format of Q&As. I prefer using syntax or terminologies that fit better rather than the more standard ones.

Q: What is cubical type theory?

A: It’s a type theory giving homotopy type theory its computational meaning.

Q: What is homotopy type theory then?

A: It’s traditional type theory (which refers to Martin-Löf type theory in this Q&A) augmented with higher inductive types and the univalence axiom.

On Writing a ComputerCraft OS

One of the most common projects I've seen for ComputerCraft is to write an operating system. People look at the limited command-line interface that CraftOS provides, and think, "I want this to work like my normal computer does!" Time and time again, a new post pops up on the ComputerCraft forums or Discord either announcing an OS, or asking for help with an OS, or releasing an OS. Usually, there are some very obvious flaws in these "OS"es, ranging from poor design choices, to overstating what they are and underdelivering. There are many common misunderstandings and undersights that newbie developers run into when writing an operating system, and these end up creating mediocre products at best.

A Critical Distinction

The term "OS" is thrown around a lot, and in my opinion it's very overused. According to [Wikipedia]: "An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs." However, m

List of "Essential" 1.7.10 Mods

This is a list of Minecraft 1.7.10 mods that are not focused on adding new original content. Instead, they make the base game run better, or port over features from other versions of vanilla.

These lists try to comprehensively list all the available options. You will not want to use all of the listed mods at once.

Some of the listed mods require a Mixin bootstrap mod in order to work. See the Mixin mods section near the end of the document for information about that.

as does a huge number of things. Probably too many. Here's a comprehensive list of everything it can do. Entries in italics are the names of functions that actually exist in the standard library, while all entries attempt to have a descriptive name for what a function that does the same thing as that particular as would do.

int <-> int
- zero_extend: unsigned int -> bigger unsigned int. Pads the number with leading zeroes. This preserves the numeric value.
- sign_extend: signed int -> bigger signed int. Pads the number with leading zeroes if positive, and leading ones if negative. This preserves the numeric value.
- truncate: bigger int -> smaller int (regardless of signedness). Throws away the high bits of the number.
- reinterpret_sign: int -> int of the same size and opposite signedness. Does nothing to the bits.
int <-> float
cast_saturate_to_infinity: Yields the float closest to the specified integer. Yields infinity if the integer is out of boun

By default Linux distros are unoptimized in terms of I/O latency. So, here are some tips to improve that.

Most apps still don't do multi-threaded I/O access, so it's a thread-per-app which makes per-app speed always bottlenecked by single-core CPU performance (that's not even accounting for stuttering on contention between multiple processes), so even with NVMe capable of 3-6 GB/s of linear read you may get only 1-2 GB/s with ideal settings and 50-150/100-400 MB/s of un/buffered random read (what apps actually use in real life) is the best you can hope for.

All writes are heavily buffered on 3 layers (OS' RAM cache, device's RAM cache, device's SLC-like on-NAND cache), so it's difficult to get real or stable numbers but writes are largelly irrelevant for system's responsiveness, so they may be sacrificed for better random reads.

The performance can be checked by:

`fio --name=read --readonly --rw={read/randread} --ioengine=libaio --iodepth={jobs_per_each_worker's_command} --bs={4k/2M} --direct={0/1} --num

VirGL for Linux KVM guests on Ubuntu Desktop

NOTE: Please don't ask for help here, it was a miracle that I got it to work at all. Seek answers in the usual places (yes, even Stackoverflow knows more than I do).

The question: How can I get 3d accelerated graphics for Linux guests in KVM without using PCI passthrough?

The short answer is: Use VirGL. The long answer is more complicated, because the VirGL project has had slow but steady progress towards actually working reliably, but the degree to which any given Linux distribution (or related driver project) is in sync has varied greatly over time. Even if it works right now, today, on your machine, it might not tomorrow. Note that even when it works, graphics performance is mediocre to downright painful.

Tested on Ubuntu Desktop 22.04.04 LTS with qemu-kvm, in an "Ubuntu on Xorg" session (not Wayland). Linux quests must have spice-vdagent installed (Ubuntu installs this by default). The hardware is a AMD 5600G d

	/*** MIT LICENSE
	Copyright (c) 2022 torcado

	Permission is hereby granted, free of charge, to any person
	obtaining a copy of this software and associated documentation
	files (the "Software"), to deal in the Software without
	restriction, including without limitation the rights to use,
	copy, modify, merge, publish, distribute, sublicense, and/or sell
	copies of the Software, and to permit persons to whom the
	Software is furnished to do so, subject to the following

	///////////////////////////////////////////////////////////////////////////////
	// ABOUT: A unity Shader .cginc to draw numbers in the fragment shader
	// AUTHOR: Freya Holmér
	// LICENSE: Use for whatever, commercial or otherwise!
	// Don't hold me liable for issues though
	// But pls credit me if it works super well <3
	// LIMITATIONS: There's some precision loss beyond 3 decimal places
	// CONTRIBUTORS: yes please! if you know a more precise way to get
	// decimal digits then pls lemme know!
	// GetDecimalSymbolAt() could use some more love/precision