C++ in the kernel

Pieter Dumon pieter.dumon at gmail.com
Sun Jan 4 10:30:33 PST 2009

It's just political, there's pros and cons for everything.
Its not because LT says something that it's true.
Some people have demonstrated nice work in C++ (e.g. some L4 variants).
Whatever language you use, it all comes down to using it properly.
But if your whole kernel is written in C, better to leave it at that :-)
The worst thing you can do is mix and match C and C++ I think - that
would be really crappy.

On Sun, Jan 4, 2009 at 5:25 PM, B. Estrade <estrabd at gmail.com> wrote:
> On Sun, Jan 04, 2009 at 05:06:13PM +0100, Michael Neumann wrote:
>> This question bugs me since a quite long time so I write it down...
>> FreeBSD had a long thread about pros and cons of using C++
>> in the kernel here [1].
>> I'm undecided whether it would be good to use C++ in the DragonFly kernel.
>> At first, most importantly, there is the question about the quality of
>> the C++ compiler (bug-freeness) and the quality of the generated machine
>> code.
>> I can't answer this for sure, just did a small test compiling
>> the same C code with both a C and a C++ compiler. Both produce the same
>> machine code.. Using C++ classes without all the more advanced stuff
>> (like exception, RTTI...) shouldn't make too much a difference in the
>> produced code. So I don't think this will be much of a problem.
>> Next thing to consider is the possible abuse of C++'s features
>> (exceptions, RTTI etc.). I don't think this is a problem either,
>> especially in a small project like DragonFly, as there is only a handful
>> of developers. The solution to this problem is as simple as just don't
>> use those features.
>> Now to the advantages of C++ that IMO would make sense:
>>   * Think about the kobj and the driver architecture. All this comes
>>     for free when using C++. No .m files anymore. Everything in
>>     one language.
>>   * Think about macro-driven datastructures (e.g. rbtree).
>>     They are IMHO quite unreadable and very hackish.
>>     C++ templates on the other hand are a lot cleaner
>>     (they are sometimes ugly as well :).
>>     Of course templates doesn't help when using internal
>>     datastructures like sys/queue.h.
>> Maybe I spent too much time using OO languages (like Ruby or C++).
>> What I am missing most in C is the ability to subclass structures,
>> methods and templates. All this IMHO can improve expressability
>> and code quality.
> I can't pretend to know what this implies for DfBSD, I think Linus has
> addressed this before wrt Linux:
>  http://lwn.net/Articles/249460/
> I don't know enough C++ to share his opinion, nor do I contribute to
> any projects, but I think this might be some good background on the
> matter.
> Cheers,
> Brett
>> Regards,
>>   Michael
>> [1]http://lists.freebsd.org/pipermail/freebsd-arch/2007-October/006969.html

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