Thor – A minimalistic operating system in assembly and C++

https://github.com/wichtounet/thor-os#thor-os

by ingve • 10 years ago

189 146 10 years ago

Jaruzel2• 10 years ago

Last week I read the very good 'How to build an operating system from scratch' [1], and I'm glad I did. It meant that I could burrow into the files on this github project and understand exactly what was going on.

One day, when I finally have some free time, I am totally going to do this myself.

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[1] https://www.cs.bham.ac.uk/~exr/lectures/opsys/10_11/lectures...

gravypod4• 10 years ago

Check out the broken thorn tutorials on the subject. They are far more complete.

Jaruzel2• 10 years ago

I will!

I'm guessing you mean these..?

http://www.brokenthorn.com/Resources/OSDevIndex.html

blackflame7000• 10 years ago

I read this same exact article last week too, what are the odds! Definitely have the same mindset to write my own someday. This project will be a ton of help.

xhrpost• 10 years ago

That looks awesome! I did a little side project on rolling my own Unix kernel, highly recommend the guide! https://web.archive.org/web/20160301082842/http://www.jamesm...

kschmit90• 10 years ago

Weow, excellaent reply budday.

jordigh2• 10 years ago

An OS in C++?

But Linus said...

http://harmful.cat-v.org/software/c++/linus

erikj• 10 years ago

That's Linus's opinion, yes. Not everyone has to share it.

jordigh2• 10 years ago

It's a really annoying widespread opinion. I've been looking for people who really do write OSes in modern C++.

tmptmp4• 10 years ago

Yes, but his opinion counts more than some John Doe's as Linus supports his case with solid arguments.

tboneatx• 10 years ago

I agree 100% with Linus, especially the boost comment. It was heavily used in a project I worked on and "boost" soon became a curse word.

garaetjjte• 10 years ago

I don't agree with Linus, but yes, boost is horrible.

leaningtower2• 10 years ago

You should not really judge a tool by the bad use the people make of it. Hammers are perfectly fine with nail but they are horrible at cutting bread

zer0gravity• 10 years ago

I do believe that when programming at "machine level" your language needs to be as simple and straightforward as possible. It needs to obey you like a sword. Yes, you need some mastery, but you know that your every action is effective. No lost effort, no mind tricks, no unnecesary complexity.

I find that every abstraction level makes me more unhappy and somehow lost..

So yes, I do believe Linus knows something and for sure he's not trying to fool himself. When you really try to build something to actually be used, all those abstractions will bite you..

TFortunato4• 10 years ago

As other's have stated, that is just Linus's opinion, which he is entitled to. It's also even understandable given his position managing all of the Linux kernel and git development work, and the large number of people who contribute (or try to anyways...) If you don't want people to blow their damn leg off, don't give them a shotgun (http://programmers.stackexchange.com/questions/92126/what-di...).

That said, this absolutely doesn't mean that you CAN'T do systems level programming in C++. I've actually done real RTOS and motor control work on a small embedded platform that went in a robot using C++! This is in an actual shipping product too, not just a hobby project...

As Linus said, it's definitely easier to come up with something inefficient in C++, and you do have to limit yourself to a sane set of features. That said, I think some of the things C++ brings to the table can make development a lot easier without sacrificing performance as long as you have a disciplined team and sane coding guidelines. But what makes sense for a personal project or a small team may not make sense for a larger project, and while I think Linus is justified in his opinion, you definitely shouldn't take it to mean that you CAN'T do systems programming in C++.

minipci13213• 10 years ago

Totally agreed with your comment until that:

as long as you have a disciplined team and sane coding guidelines

Is it not possible at all anymore to just hire people actually understanding what they are doing? Or cargo cult is here to stay?

I am sorry - please don't take that as a personal attack, but explaining people that C++ can actually be used in OS development by mindlessly sticking to some rules doesn't seem a way to me... but rather a counter-argument to what you said yourself.

jmnicolas• 10 years ago

Aren't large parts of Windows written in C++ ?

TFortunato4• 10 years ago

I'm pretty sure it is! ( I'm also pretty sure that for a subset of the HN crowd, you may have just proven Linus's point :-P )

ekr• 10 years ago

The kernel is written entirely in C. See various WRK releases you can find online.

snarfy• 10 years ago

The problem with C++ is more about collaboration than with the language. It's harder to misuse C than C++. When you have a large group of people contributing, proper usage matters. Everything Linus rants about is improper usage.

legulere• 10 years ago

On the other hand smart pointers (which I think didn't exist when linus wrote this?) and RAII make C++ harder to misuse than C.

mdellavo• 10 years ago

Does this actually use classes and other features of C++? Scanning a few files on Github I see namespaces being used but not much else.

Very impressive either way - I was just curious how C++ was leveraged.

wichtounet7• 10 years ago

I'm using a few classes and some class hierarchy as well. I've reimplemented std::vector and std::string and a few other features from the STL and use them both in kernel space and user space (the STL is not standalone, need the glibc and I didn't want to port everything). I'm using quite some templates in the library part. I'm using auto from C++11 and a few constexpr functions. I have disabled exceptions and RTTI. I'm using RAII principle as much as possible (but this can be improved a lot still). I'm using references when I can remove pointers.

On the other hand, a lot of code is clearly very close to C. When you're doing some low-level things, parsing memory structures, paging, ... there are not a lot of features from C++ than can help. Moreover, there is a lot of code that could profit from some refactorings:P

pjmlp12• 10 years ago

Linus now even uses Qt for its own hobby application.

xjia• 10 years ago

s/its/his/ ?

dbcurtis5• 10 years ago

What kind of C++ are you writing? That's the real question. My friends and I that work on bare-metal talk about "embedded C++". Yes, it is C++, and you can take advantage of some C++ features, but some things are not in the mix. Like, for instance, if you have 8K of physical SRAM and no virtual memory manager, new and dispose aren't going to do a lot for you.

C++ has it's place in OS development, but you need to know exactly what code is being generated, and you need to understand with excruciating precision how memory is being allocated.

microcolonel2• 10 years ago

I prefer this one http://harmful.cat-v.org/software/c++/I_did_it_for_you_all

leaningtower2• 10 years ago

Well, when St. Linus Torvalds said those words, (1) g++ was not as good as many other C++ compilers, (2) the world was still full of very bad examples of C++: if you were lucky, back in those days you could have found some projects using C++03 but the majority were stuck to C++98 -- or worse -- and, (3) he called out the holy principle that "at my place, I make the rules". I do not think that in 2016 there are good reasons not to use C++ for an operating system. Even without using the STL -- which would require custom allocators at that level -- incapsulation of data inside objects, inheritance, templates and namespaces alone are a reasons good enough for me to prefer C++ over C at any time nowadays. In 2016, that is more a cargo cult not to use C++ for operating systems implementation than anything else.

insulanian• 10 years ago

Can an operating system be developed from scratch using a safe language such as Rust?

If yes, why people still even think about doing it with unsafe languages?

wichtounet7• 10 years ago

You can write a kernel in pretty much every language. There are some experiments with Rust: http://www.randomhacks.net/bare-metal-rust/

There are several reasons to choose a language rather than another. I personally don't like Rust at all, so I don't see any reason to use it, neither do I see any advantage in using it. But that's only my opinion. A lot of osdev currently is made by hobbyist (not counting the handful of really succesful kernels), so the main argument is simply personal and there is nothing wrong with it. Moreover, keep in mind that Rust is pretty new while C/C++ are decades old, this means more support, more portability, more people that know how to use it, ... This is not negligible at all.

nickpsecurity• 10 years ago

Forget the experiments. Try this one:

https://www.redox-os.org/

pjmlp12• 10 years ago

Sure it can and it has been done multiple times, although the industry hasn't cared much besides high integrity software, where software errors cost human lives.

For an example, check the "Project Oberon" book.

http://people.inf.ethz.ch/wirth/ProjectOberon/index.html

The revised 2013 version, with its own FPGA as replacement for the Ceres Workstation hardware of the original version.

snaky3• 10 years ago

Can an operating system be developed from scratch using a safe language such as Rust?

We don't know.

If yes, why people still even think about doing it with unsafe languages?

Because it works.

vertex-four4• 10 years ago

> Can an operating system be developed from scratch using a safe language such as Rust?
We don't know.

Sure we do. Redox[0] boots into a desktop environment with a filesystem, etc etc. What we don't really know is how performant/portable/etc you could make it if you put the same amount of manpower into it as went into <other operating system of choice>.

dbcurtis5• 10 years ago

If yes, why people still even think about doing it with unsafe languages?

What you need for OS or embedded development is a language that doesn't get in your way. C doesn't get in your way. C is the first language that both stayed out of your way and also provided reasonable productivity features (over BCPL, B, and assembly).

It was only recently that people have figured out how to come close to a "safe" language that doesn't get in your way.

Here is a test case: grab an ARM Cortex-Mx processor. Boot, configure the I/O matrix, and set up, oh say, the counter/timer peripherals for PWM motor control and quadrature decode. If you can do that without a trip to an "unsafe" language, that is a worthy accomplishment for your safe language.

Another test case might be doing page swapping and page-table updates on a virtual memory subsystem on a multi-core CPU without a trip to an unsafe language.

I guess a more direct answer to your question is that when you get down to the hardware, you have to deal with weirdo bit fields, volatile hardware registers, strange read/write ordering requirements, interlocks, and even some totally non-interlockable volatile stuff. C can do it (although I admit it uses language features not everyone sees every day).

nmjohn• 10 years ago

I guess a more direct answer to your question is that when you get down to the hardware, you have to deal with weirdo bit fields, volatile hardware registers, strange read/write ordering requirements, interlocks, and even some totally non-interlockable volatile stuff. C can do it (although I admit it uses language features not everyone sees every day).

I agree with you that building an entire OS to interface with hardware without using _any_ unsafe code is, by some definition of the word, impossible.

However that doesn't mean you must limit yourself to unsafe languages for the other 90% of the operating system code.

steveklabnik4• 10 years ago

Funny you should mention the Cortex-M :) https://github.com/helena-project/tock/ (written in Rust, just linked to it down thread as well)

pjmlp12• 10 years ago

C is the first language that both stayed out of your way and also provided reasonable productivity features

If we ignore the history of computers outside AT&T....

lgessler• 10 years ago

Dave Evans at the University of Virginia taught a class on that in Spring 2014: http://rust-class.org/

Rust has changed a lot since then, but you might take a look there.

kalsk• 10 years ago

unsafe languages

There is no such thing.

adrusi2• 10 years ago

"Why doesn't everyone agree with me that statically enforced safety is the only necessary consideration when building hobby projects?"

And yes, an operating system can be developed from scratch with Rust, maybe with a sprinkle of assembly, but every attempt I've seen makes widespread use of `unsafe', so the value mostly comes from Rust's modern type system with its traits and enums.

pcwalton• 10 years ago

every attempt I've seen makes widespread use of `unsafe', so the value mostly comes from Rust's modern type system with its traits and enums.

http://os.phil-opp.com/ follows the Rust way of making safe abstractions as much as possible.

_c_5• 10 years ago

+1 for being able to run on Bochs.

There's nothing minimalistic about Qemu. It's an enormous resource intensive program to build. And it's not even easy to run in text mode (no x11). "Qemu-lite" is sorely needed.

Sir_Cmpwn• 10 years ago

It's actually quite easy to run in text mode, just add -nographic. It automatically hooks the serial port up to your terminal, too.

_c_5• 10 years ago

What OS are you using?

Is it working for you in VGA text mode (no x11)?

Is this now working on other UNIX-like OS besides Linux?

I have had problems with -nographic in the past and I know others who have as well, but maybe it works reliably now?

adrusi2• 10 years ago

It's not minimalistic in its capabilities or implementation, but it's minimalistic in its interface. Its a tool that emulates various hardware, and provides a CLI interface that's no more complex than necessary to operate its conceptually narrow functionality.

_c_5• 10 years ago

I was referring to how long it takes to build from source and how much RAM and CPU it uses while building. The interface is fine. I love Qemu. Bellard writes great software. My early experiences with it were very good. But it has grown to become a whale of a program. I had to switch to Bochs.

revelation• 10 years ago

And the latest commit message is "Prepare ICMP message type decoding"

It seems we have not learned from the mistakes of prior operating systems and instead of a "Windows NT ping of death" we'll have a "Thor ping of death", which is a curious image, Thor brought down by a puny ping.

wichtounet7• 10 years ago

That would be impossible, Thor cannot be brought down by any other than Jörmungandr. More seriously, I'll try to avoid reproducing the ping of death issue :)

joshmarinacci2• 10 years ago

The hobbyist OSes pop up a lot on Hackernews. Some are more full featured than others. What would say is the minimum feature set to be called a real OS?

whorleater• 10 years ago

At least for my operating systems class, the requirement was to be able to boot and run a text editor, usually Vi. Didn't stop some people from building one that could run Doom though.

joshmarinacci2• 10 years ago

Ah. I was thinking something more like process isolation and device drivers.

noblethrasher• 10 years ago

Remember that since our general purpose computers are approximately Turing Machines, they can simulate anything, including better general purpose computers.

An OS is just a simulation of a "nicer" computer than the one that is natively exposed by the "real" one (i.e. the hardware).

Normally, "nicer" is pretty subjective, but in the case of computing it almost always means only two things:

* We simulate many more computers than we actually have (i.e. timesharing and multitasking)

* We simulate computers that are much easier to program.

In other words, an OS is just a simulation of having access to a bunch of nicer-to-program computers.

But, this ends up implying a multitude of features:

* Simulating many computers requires having a scheduler and process isolation. If we decide that we want individual users to have privileged access to their simulated computers, then we end up adding security features related to authorization and authentication. If we decide that the simulated computers should be able to communicate with each other, then we end up with networking since there is little difference between two simulated computers running on the same box, and two simulated computers that are running on different boxes.

* Simulating easier-to-program computers requires having memory management, virtual memory, I/O abstraction, graphics, portability, etc.

Since we end up with most, if not all, of the features that most people think are requisite for an OS, I think that my definition is minimal.

mLuby• 10 years ago

Should have called it ant-man.

Thor – A minimalistic operating system in assembly and C++

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