Is there some lore about this I don’t know?
There is no C++ allowed in the Linux kernel and Linus has gone on several major rants about how terrible a language it is.
Is it all C?
There’s assembly and makefiles too
Less of a joke answer, there has been work to allow Rust bindings for drivers.
rust too
According to the github analysis, the kernel repository is:
- C 98.3%
- Assembly 0.7%
- Shell 0.4%
- Makefile 0.2%
- Python 0.2%
- Perl 0.1%
- Other 0.1%
So yeah, its basically all C, plus a tiny bit of assembly for very low level bootstrapping and some helper scripts.
Yeah but a lot of that C code has inline assembly so it’s more like 5-10% asm.
Inline assembly is such a shit practice. But c++ bad.
Sometimes you can’t get around it though.
Afaik MSVC forbids it and it’s one of the very few nice things about c++ on windows.
If you need to write assembly don’t fucking do it in a cpp file. Create a header, an assembly file, assemble it and link to it.
Wot no Delphi?
No VB6 either 🤷♂️
How can one write a kernel without using VB6 at all?
Yeah, indeed, why not 🤔…
Lots of core UNIX and Linux projects are. C++ is not liked by a lot of low level FOSS community. I think Rust is going to get further into these areas. I know C++ well but prefer C. I know plenty of others who feel the same.
I’ve read that they are writing parts of the kernel in Rust
Yes, I think Rust is a better C++ and will replace it in many places. Though all three will be around for ever to be honest.
Yes, first Rust code was released in 6.6 I think and MS also started implementing Rust code in the Windows kernel.
Rust is certainly interesting. I think it’s the C++ we need.
Personally I find the syntax unreadable.
Always has been
Why do I suddenly feel a meme coming on? 😅
Then why does he write C++?
https://github.com/subsurface/subsurface/commit/1b16d570a1b6700295153bd6597b148b65000458
Torvalds just really dislikes C++. He’s gone on the record saying that he thinks it’s just not a good language. In his own words “C++ is just a waste, there is no design at all, just adding some scum on top of C.”
he’s not wrong
In the specific use case of kernel programming, maybe. But the Standard Template Library is awesome.
they dumped everything in the languaga, at least samething they needed to have right, it’s otherwise statistically impossible
The STD is maybe the only good thing C++ has over C, and even that is awful compared to other language’s standard libraries.
I can’t name another good thing C++ has. Maybe templates. C++’s reliance on inheritance for polymorphism is awful (should’ve gone with interfaces/traits).
Not to mention the mess with all the different types of constructors that must always be implemented.
It’s just a bunch of bad design choices added on top of an old outdated language.
The STD is maybe the only good thing C++ has over C, […]. I can’t name another good thing C++ has. Maybe templates.
Are you high? I was praising the STL, you know, the template library?
Never before have I been so offended by something I 100% agree with.
I would have agreed with that before C++11. But since then, C++ has improved a lot. Its like the vision of what C++ suddenly became more clear. So I wonder if Linus would still say that today. (Unfortunately, there have been a lot of missteps in the development of C++ though, and so there is a lot of cruft that everyone wishes was not there…)
”C++ is a horrible language. It’s made more horrible by the fact that a lot of substandard programmers use it, to the point where it’s much much easier to generate total and utter crap with it. Quite frankly, even if the choice of C were to do nothing but keep the C++ programmers out, that in itself would be a huge reason to use C.”
I don’t know about Linus, but the last time Reiser’s wife was seen, she was writing a c++ hello world
Too soon.
For an example from the other poster’s explanation:
https://lwn.net/Articles/249460/
This was pre c++11 - not sure if he’s changed his mind at all with more modern c++
He absolutely has not.
That’s my guess, but there was a conversation on the mailing list a few months ago that wasn’t just immediately shut down, even by other prolific developers
Ts’o seems skeptical, but is at least asking whether c++ has improved
Take a look at what even the proposer is saying wouldn’t be allowed in:
(1) new and delete. There's no way to pass GFP_* flags in. (2) Constructors and destructors. Nests of implicit code makes the code less obvious, and the replacement of static initialisation with constructor calls would make the code size larger. (3) Exceptions and RTTI. RTTI would bulk the kernel up too much and exception handling is limited without it, and since destructors are not allowed, you still have to manually clean up after an error. (4) Operator overloading (except in special cases). (5) Function overloading (except in special inline cases). (6) STL (though some type trait bits are needed to replace __builtins that don't exist in g++). (7) 'class', 'private', 'namespace'. (8) 'virtual'. Don't want virtual base classes, though virtual function tables might make operations tables more efficient.C++ without
class, constructors, destructors, most overloading and the STL? Wow.That doesn’t really surprise me, as most of those are the same requirements from any embedded development use case using c++ that I’ve worked on
4 and 5 are the only ones stricter than I’m used to
I’ve only worked on a few embedded systems where C++ was even an option, but they allowed 2, 4, 5, and 7. Though, for the most part most classes were simple interfaces to some sort of SPI/I2C/CAN/EtherCAT device, most of which were singletons.
time to go pedantic and use parts of the c++stdlib that weren’t included in the stl!
I don’t think its the ergonomics of the language he has an issue with. If anything C++1x probably just made the original critiques of bloat worse.
In that post, his critiques were around the problems with the STL and everyone using Boost. The STL has improved significantly since then, and it would be a limited subset of c++ if it was ever allowed
There have been mailing list conversations earlier this year, citing that clang/gcc now allowing c++ in their own code might mean they’ve taken care of the issues that made it unusable for kernel code
https://lore.kernel.org/lkml/[email protected]/
I’m not saying it will happen, but it’s not being shot down as an absolute insanity anymore, and I wouldn’t have expected Rust to be allowed in the kernel, either
Oh interesting. I didn’t realize boost was the main issue. Most people I’ve talked to were complaining about VTables introducing a bunch of indirection and people blindly using associative containers.
Vtable equivalents are used extensively in the kernel
You’ll find structs all over the place setting them up, e.g. every driver sets up a .probe function that the core will call, since it doesn’t know what driver it’s loading
Right the issue was more because they’re so easy to throw in without thinking about it so people overuse them. That may just be older devs complaining about newbies though.
”C++ is a horrible language. It’s made more horrible by the fact that a lot of substandard programmers use it, to the point where it’s much much easier to generate total and utter crap with it. Quite frankly, even if the choice of C were to do nothing but keep the C++ programmers out, that in itself would be a huge reason to use C.”
Literally apply that train of thought to JavaScript and JavaScript is in an even worse position than C++
JavaScript has the Node.js community in it and that just says it all really.
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Linus is a C advocate btw, which make him even more goated
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The day I learned that Linus shares my disdain for all things OOP was such a good day for me.
Me, when Linus’ opinion is different to mine: “Linus has such weirdly strong opinions about this”
Me when Linus’ opinion is the same as mine: VINDICATION
peak hairless ape
I feel the OOP debate got a bit out of hand. I hate OOP as well, as a paradigm.
But I love objects. An object is just a struct that can perform operations on itself. It’s super useful. So many problems lend themselves to the use of objects.
I’ve been writing a mix of C and C++ for so long I don’t even know where the line is supposed to be. It’s “C with objects”. I probably use only 1% of the functionality of C++, but that 1% is a huge upgrade from bare C IMO.
Agreed. Objects are nice and a great way to program. Composition is great. Traits/interfaces are great. Namespaces are great. Objects are a really nice way to reap the benefits of principles like these.
But then there are aspects of OOP that absolutely suck, like inheritance. I hate inheritance. The rules get very confusing very quickly. For example, try understanding overriding of methods. Do I need to call the superclass method or not? If not, does it get called automatically? If so, in what order? How do these rules change for the constructor? Now repeat this exercise for every OOP language you use and try not to mix them up… Java, C++, Python, etc.
Fortunately, it feels like we rely on inheritance less and less these days. As an example, I really like how Java allows you to implement
Runnablethese days. Before, if you wanted to run a thread, you needed a separate object that inheritedThread. And what if that object needs to inherit from another one too? Things would get out of hand quickly. (This is a very old example, but with lambdas and other new features, things are getting even better now.)Anyway, long story short, I think OOP is a complicated way to achieve good principles, and there are simpler ways to achieve those principles than a full OOP implementation.
I’ve seen this thing where people dislike inheritance a lot, and I have to admit that I kind of struggle with seeing the issue when it’s used appropriately. I write a bunch of models that all share a large amount of core functionality, so of course I write an abstract base class in which a couple methods are overridden by derived models. I think it’s beautiful in the way that I can say “This model will do X, Y, Z, as long as there exists an implementation of methods A, B, C, which have these signatures”, then I can inherit that base class and implement A, B, and C for a bunch of different cases. In short, I think it’s a very useful way to express the purpose of the code, without focusing on the implementation of specific details, and a very natural way of expressing that two classes are closely related models, with the same functionality, as expressed by the base class.
I honestly have a hard time seeing how not using inheritance would make such a code base cleaner, but please tell me, I would love to learn.
What you’re describing is an interface. An interface is a contract that ensures you can do something, but doesn’t care how.
Abstract classes can have abstract functions. When you do this, you’re basically just creating a base class with an interface on top; you’re saying “all my children must implement this interface of mine” without having to actually make a separate interface.
Abstract classes also offer additional functionality though, such as the ability to define properties, and default implementations of methods. You can even utilize the base class implementation of the method in your child class, in order to perform extra steps or format your input before you do whatever it is you were doing in the first place.
So, an interface is a contract that allows you to call a method, without having to know the specific class or implementation.
Inheritance is more like “it does everything that X does, but it also does Y and Z.” If you’re ever finding yourself writing an abstract class with purely abstract methods, you probably want to write an interface instead. That way, you get all the same functionality, but it’s more loosely coupled
Epecially when you think in “real” OOP terms:
Abstract classes are “child is a parent”, fx “duck is a bird”. Bird describes all the traits that all birds have in common. But not all birds fly, so flight must come from an interface. This interface can be passed around to any number of objects, and they’re not as tightly coupled because unlike an abstract class, an interface doesnt imply that “duck is a flight”. The interface is just something we know the duck can do.
As you can probably tell, I work with OOP on a daily basis and have for years. There are a lot of valid criticisms of the OOP philosophy, and I have heard a lot of good points for the record. I am just educating on the OOP principles because you said you were interested and to clear up any misconceptions.
Well yes, I get the differerence between an interface and a class, and what I write is typically a class, which contains properties and functionality that may or may not be overridden in derived classes.
For example, calling a parent class implementation can be useful when I have a derived model that needs to validate its input in some specific way, but otherwise does the same as the base class.
What I don’t understand is why this makes OOP bad?
I think the problem with OOP is something you can see whenever legislation is linked with prestige (it happens a lot in real life). The number of good possible rules is quite limited, and the number of people who want to make a name for themselves by championing them seems to be infinite. If you can’t find a good rule to claim as your own, you have to pick a bad rule and try to gaslight people into thinking it’s a necessary and beneficial. Enough people do that, and we end up with modern OOP.
He is is OK with OOP. The Linux kernel is full of OPP C, but he doesn’t like C++
He writes Qt C++ for his diving app though.
I think Linus did it in C with GTK but who took it moved it C++ and Qt. Lazy searching didn’t dig up the story.
It was originally Gtk and they rewrote it with Qt: https://www.youtube.com/watch?v=gGZyVSOnqm0
But Linus does write C++/Qt code: https://github.com/subsurface/subsurface/commit/1b16d570a1b6700295153bd6597b148b65000458
I write C++, but I don’t like it. I don’t think any one should be claiming Linus doesn’t like it because he doesn’t know it. If he wants to contribute to this project, it must be C++.
I don’t think any one should be claiming Linus doesn’t like it because he doesn’t know it
I didn’t think anyone was making that claim? Either way I’m certainly not trying to.
If he wants to contribute to this project, it must be C++.
Yes, this is true, it’s just that he was also included in the decision making process to switch to it in the first place, and I feel like his continued use of it makes me think it doesn’t have to be as awful as everyone makes it out to be, or he wouldn’t use it at all.
Ask him. It’s not like he has publically changed his mind. I think he just went with other developers he had handed the project to.
He’s not though, you should look into it
Look at the kernel code. It’s full of OOP C. There absolutely are objects in the kernel.
Yea but all that function pointer indirection can actually hurt performance (especially caching), some things in C++ actually can be faster just because the compiler is better at optimizing for that.
There is nothing you can do in C++ or C, that can’t be done in the other. It’s the kind of the point of those languages.
Technically you’re right, but I don’t think that changes what I said about optimization. There are still cases where equivalent C++ code can be faster than the C version merely due to different optimizations used.
Meh, I’m unconvinced. If it’s any kind of hot spot, in either, you can optimize the hell out of it. C++ is often more bloated is it’s just a harder language pretending to be an easier one.
I know it is a complete joke. But every time i think of c++ i am reminded of this prank article https://www-users.york.ac.uk/~ss44/joke/cpp.htm
I wonder what would offend Linus more: A version of the Linux Kernel with C++ or one that breaks the userspace…
A PHP kernel?
That’s just a crime against humanity.
You know you want a PHP distribution with a JavaScript interface. Don’t lie to yourself.
The PHP Gtk bindings used to be built-in to PHP as one of the standard extensions. I think they split it out at some point.
I found this site with a few apps built using it: https://cweiske.de/phpgtk_apps.htm
Jesus… people really have nothing better to do, huh…
Uuuuu… you done it now 😬…
Hauge
The Indian distro BOSS Linux actually uses C++ modules in their kernel fork.
Mic looks like earring, can’t unsee it…
Assembly it is, then
That’s the Linux equivalent of calling someone an idiot sandwich.
What’s wrong with c++?
For kernel dev it would be a disaster, there’s too much implicit action, and abstractions that have unknown runtime cost. The classic answer is that everyone uses 10% of its features over C, but nobody can agree on which 10%.
As someone forced to get up to date with C++ recently, at this point it’s a language in full identity crisis. It wants so badly to be Rust, but it’s got decades of baggage it’s dragging along.
And now there is precedent for Rust components in the Linux kernel.
It do be like that… a lot of old languages want to be Rust…
What’s wrong with C? Just write a module
- My dad
10 in binary as well
Rapid Abandonment Is Imperative
