this post was submitted on 13 Apr 2024
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submitted 2 months ago by [email protected] to c/linuxmemes
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[–] ozymandias117 25 points 2 months 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++

[–] [email protected] 11 points 2 months ago (1 children)

He absolutely has not.

[–] ozymandias117 4 points 2 months ago* (last edited 2 months ago) (1 children)

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/[email protected]/

[–] [email protected] 12 points 2 months ago* (last edited 2 months 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.

[–] ozymandias117 10 points 2 months 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

[–] [email protected] 5 points 2 months 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.

[–] [email protected] 1 points 2 months ago

time to go pedantic and use parts of the c++stdlib that weren't included in the stl!

[–] nandeEbisu 3 points 2 months ago (1 children)

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.

[–] ozymandias117 13 points 2 months ago (1 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/[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

[–] nandeEbisu 1 points 2 months ago (1 children)

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.

[–] ozymandias117 2 points 2 months ago* (last edited 2 months ago) (1 children)

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

[–] nandeEbisu 2 points 2 months ago

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.