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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.
Exactly my thoughts 👍.
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.
”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.
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.
Linus is a C advocate btw, which make him even more goated