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[–] 92 points 2 years ago (10 children)

Is there some lore about this I don't know?

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  • [–] 137 points 2 years ago (2 children)

    There is no C++ allowed in the Linux kernel and Linus has gone on several major rants about how terrible a language it is.

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  • [–] 53 points 2 years ago (4 children)
  • [–] 85 points 2 years ago (2 children)

    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.

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  • [–] 30 points 2 years ago (1 child)

    Yeah but a lot of that C code has inline assembly so it's more like 5-10% asm.

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  • [–] 13 points 2 years ago (1 child)

    Inline assembly is such a shit practice. But c++ bad.

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  • [–] 17 points 2 years ago (1 child)

    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.

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  • [–] 3 points 2 years ago (1 child)

    I've read that they are writing parts of the kernel in Rust

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  • [–] 4 points 2 years ago (2 children)

    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.

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  • [–] 76 points 2 years ago (3 children)

    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."

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  • [–] 55 points 2 years ago (1 child)
  • [–] 32 points 2 years ago (2 children)

    In the specific use case of kernel programming, maybe. But the Standard Template Library is awesome.

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  • [–] 2 points 2 years ago* (1 child)

    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.

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  • [–] 12 points 2 years ago

    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...)

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  • [–] 25 points 2 years ago (2 children)

    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++

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  • [–] 11 points 2 years ago (1 child)
  • [–] 4 points 2 years ago* (1 child)

    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

    https://lore.kernel.org/lkml/20240110175755.GC1006537@mit.edu/

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  • [–] 12 points 2 years ago* (2 children)

    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.

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  • [–] 10 points 2 years ago (2 children)

    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

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  • [–] 5 points 2 years ago

    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.

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  • [–] 3 points 2 years ago (1 child)

    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.

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  • [–] 13 points 2 years ago (3 children)

    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/e5949a27-999d-4b6e-8c49-3dbed32a00bc@zytor.com/

    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

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  • [–] 25 points 2 years ago (1 child)

    ”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.”

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

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