5486 - draft synthesis of Mu and SubX descriptions
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Kartik Agaram
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Readme.md
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Readme.md
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## SubX: A minimalist assembly language for a subset of the x86 ISA
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# Mu: a _human-scale_ computer
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SubX is a simple, minimalist stack for programming your computer.
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* Not designed to operate in large clusters providing services for millions of
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people.
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* Designed for _you_, to run one computer. (Or a few.)
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Goals (in priority order):
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* [Reward curiosity.](http://akkartik.name/about)
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* Easy to build, easy to run.
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* All design decisions comprehensible to a single individual. (On demand.)
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* All design decisions comprehensible without needing to talk to anyone.
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(I always love talking to you, but I try hard to make myself redundant.)
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* [A globally comprehensible _codebase_ rather than locally clean code.](http://akkartik.name/post/readable-bad)
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* Safe.
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* Thorough test coverage. If you break something you should immediately see
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an error message. If you can manually test for something you should be
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able to write an automated test for it.
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* Memory leaks over memory corruption.
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* Clear error messages over expressive syntax.
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* Teach the computer bottom-up.
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* [Minimal dependencies](http://akkartik.name/post/libraries2), so that
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installation is always painless.
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Non-goals:
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* Efficiency. Clear programs over fast programs.
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* Portability. Runs on any computer as long as it's x86.
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* Compatibility. The goal is to get off mainstream stacks, not to perpetuate
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them. Sometimes the right long-term solution is to [bump the major version number](http://akkartik.name/post/versioning).
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* Syntax. Mu code is meant to be comprehended by [running, not just reading](http://akkartik.name/post/comprehension).
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For now it's a thin veneer over machine code. I'm working on memory safety
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before expressive syntax.
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What I have so far: a self-hosted tool (SubX) for writing thoroughly tested
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x86 machine code atop a bare Linux kernel. Eventually you will be able to
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program in higher-level notations. Eventually Mu won't need Linux or C.
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Eventually the OS interfaces for screen, keyboard, file system and network
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will be _dependency-injected_ so that tests can easily insert a fake screen,
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keyboard, file system or network.
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The rest of this Readme describes SubX.
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## SubX is a simple, minimalist stack for programming your computer.
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```sh
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$ git clone https://github.com/akkartik/mu
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$ cd mu/subx
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$ cd mu
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$ ./subx # print out a help message
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```
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SubX is designed:
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* to enable automation of arbitrary manual tests
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* to be easy to implement in itself, and
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* to help learn and teach the x86 instruction set.
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It requires a Unix-like environment with a C++ compiler (Linux or BSD or Mac
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SubX requires a Unix-like environment with a C++ compiler (Linux or BSD or Mac
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OS). Running `subx` will transparently compile it as necessary.
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[](https://travis-ci.org/akkartik/mu)
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You can hack on it, and its thorough tests will raise the alarm when you break
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something.
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Eventually you will be able to program in higher-level notations. But you'll
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always have tests as guardrails and traces for inspecting runs. The entire
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stack will always be designed for others to comprehend. You'll always be
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empowered to understand how things work, and change what doesn't work for you.
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You'll always be expected to make small changes during upgrades.
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## What it looks like
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Here is the first example we ran above, a program that just returns 42:
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- syntax for addressing modes: `%reg`, `*reg`, `*(reg+disp)`,
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`*(reg+reg+disp)`, `*(reg+reg<<n + disp)`
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- function calls in a single line, using addressing modes for arguments
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- syntax for controlling a type checker, akin to the top-level Mu language
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- syntax for controlling a type checker, like [prototype 2](https://github.com/akkartik/mu/tree/master/archive/2.vm).
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- a register allocation _verifier_. Programmer provides registers for
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variables; verifier checks that register reads are for the same type that
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was last written -- across all control flow paths.
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@ -736,6 +764,16 @@ from a slice:
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* `skip-chars-matching-in-slice`: curr, end, delimiter byte -> new-curr (in `EAX`)
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* `skip-chars-not-matching-in-slice`: curr, end, delimiter byte -> new-curr (in `EAX`)
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## Resources
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* [Single-page cheatsheet for the x86 ISA](https://net.cs.uni-bonn.de/fileadmin/user_upload/plohmann/x86_opcode_structure_and_instruction_overview.pdf)
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(pdf; [cached local copy](https://github.com/akkartik/mu/blob/master/subx/cheatsheet.pdf))
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* [Concise reference for the x86 ISA](https://c9x.me/x86)
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* [Intel processor manual](http://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-instruction-set-reference-manual-325383.pdf) (pdf)
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- [“Bootstrapping a compiler from nothing”](http://web.archive.org/web/20061108010907/http://www.rano.org/bcompiler.html) by Edmund Grumley-Evans.
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- [“Creating tiny ELF executables”](https://www.muppetlabs.com/~breadbox/software/tiny/teensy.html) by Brian Raiter.
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- [StoneKnifeForth](https://github.com/kragen/stoneknifeforth) by [Kragen Sitaker](http://canonical.org/~kragen).
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## Conclusion
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The hypothesis of Mu and SubX is that designing the entire system to be
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* There would be a stronger culture of reviewing the code for programs you use
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or libraries you depend on. [More eyeballs would make more bugs shallow.](https://en.wikipedia.org/wiki/Linus%27s_Law)
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## Resources
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## Credits
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Mu builds on many ideas that have come before, especially:
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- [Peter Naur](http://akkartik.name/naur.pdf) for articulating the paramount
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problem of programming: communicating a codebase to others;
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- [Christopher Alexander](http://www.amazon.com/Notes-Synthesis-Form-Harvard-Paperbacks/dp/0674627512)
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and [Richard Gabriel](http://dreamsongs.net/Files/PatternsOfSoftware.pdf) for
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the intellectual tools for reasoning about the higher order design of a
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codebase;
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- Unix and C for showing us how to co-evolve language and OS, and for teaching
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the (much maligned, misunderstood and underestimated) value of concise
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*implementation* in addition to a clean interface;
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- Donald Knuth's [literate programming](http://www.literateprogramming.com/knuthweb.pdf)
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for liberating "code for humans to read" from the tyranny of compiler order;
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- [David Parnas](http://www.cs.umd.edu/class/spring2003/cmsc838p/Design/criteria.pdf)
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and others for highlighting the value of separating concerns and stepwise
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refinement;
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- [Lisp](http://www.paulgraham.com/rootsoflisp.html) for showing the power of
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dynamic languages, late binding and providing the right primitives *a la
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carte*, especially lisp macros;
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- The folklore of debugging by print and the trace facility in many lisp
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systems;
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- Automated tests for showing the value of developing programs inside an
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elaborate harness;
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- [Python doctest](http://docs.python.org/2/library/doctest.html) for
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exemplifying interactive documentation that doubles as tests;
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- [ReStructuredText](https://en.wikipedia.org/wiki/ReStructuredText)
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and [its antecedents](https://en.wikipedia.org/wiki/Setext) for showing that
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markup can be clean;
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- BDD for challenging us all to write tests at a higher level;
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- JavaScript and CSS for demonstrating the power of a DOM for complex
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structured documents.
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- Rust for demonstrating that a system-programming language can be safe.
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- Forth for demonstrating that ergonomics don't require grammar.
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## Coda
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* [Single-page cheatsheet for the x86 ISA](https://net.cs.uni-bonn.de/fileadmin/user_upload/plohmann/x86_opcode_structure_and_instruction_overview.pdf)
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(pdf; [cached local copy](https://github.com/akkartik/mu/blob/master/subx/cheatsheet.pdf))
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* [Concise reference for the x86 ISA](https://c9x.me/x86)
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* [Intel processor manual](http://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-instruction-set-reference-manual-325383.pdf) (pdf)
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* [Some details on the unconventional organization of this project.](http://akkartik.name/post/four-repos)
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## Inspirations
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* [“Creating tiny ELF executables”](https://www.muppetlabs.com/~breadbox/software/tiny/teensy.html)
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* [“Bootstrapping a compiler from nothing”](http://web.archive.org/web/20061108010907/http://www.rano.org/bcompiler.html)
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* Forth implementations like [StoneKnifeForth](https://github.com/kragen/stoneknifeforth)
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* Previous prototypes: [mu0](https://github.com/akkartik/mu0), [mu1](https://github.com/akkartik/mu1).
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