Date: Tue, 11 Jul 2006 23:37:52 +0200 From: "Attilio Rao" <attilio@freebsd.org> To: "mag@intron.ac" <mag@intron.ac> Cc: freebsd-hackers@freebsd.org Subject: Re: kern/99979: Get Ready for Kernel Module in C++ Message-ID: <3bbf2fe10607111437h6547432fn2887348708df29a4@mail.gmail.com> In-Reply-To: <1152642474.29859@origin.intron.ac> References: <84dead720607092015q7f1701abse143f3855c2aa95a@mail.gmail.com> <44B2D2DF.2000401@sh.cvut.cz> <86sll8zl9x.fsf@xps.des.no> <courier.44B35DBC.00003F75@intron.ac> <86fyh8zgw8.fsf@xps.des.no> <courier.44B37714.00004B4D@intron.ac> <868xn0z8w9.fsf@xps.des.no> <courier.44B3B9A0.0000609C@intron.ac> <20060711152949.GB1463@merlin.emma.line.org> <1152642474.29859@origin.intron.ac>
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2006/7/11, mag@intron.ac <mag@intron.ac>: > Why do you all consider importing C++ code to FreeBSD kernel to be so > complicated at the beginning? > > Matthias Andree wrote: > > > (please don't Cc me on list replies; chopping down the Cc list) > > > > On Tue, 11 Jul 2006, mag@intron.ac wrote: > > > >> Just as you said, C++ is more complicated than C. However, without > >> C++ exception and other advanced features, it hasn't brought much > >> complexity to C++ runtime library. Early C++ compiler even translates > >> C++ code into C code before real compilation. > > > > But what's the point of C++ if it is mutilated below minimum standard > > compliance levels so that you can no longer call it C++? > > > > This discussion has been through for other systems such as Linux long > > ago, and it wasn't lack of manpower, but lack of technical feasibility, > > or in other words, what was still useful for a kernel wasn't that much > > different from C any more. C99 already adressed several concerns of C89, > > and ISTR that FreeBSD kernels are C99 code these days. > > > >> We can judge whether a C++ feature can or cannot be imported into FreeBSD > >> kernel by assemble code generated by GNU CC. > > > > Great, make the whole kernel depend on compiler internals. > > Can you imagine a single vendor who'd have interest in hauling so many > > dependencies into their software and handle all the support? I can't. > > Please complain about the portability of runtime library after reading > codes in /usr/src/contrib/libstdc++/libsupc++/. > Are they really so difficult to port? > > > > > Write a C stub and put the rest into userspace where C++ works. > > > >> For example, I think C++ exception handling is really poorly suited for > >> low-level code. > > > > Which chops off one of C++'s legs to stand on. > > Aside from the complexity of implementing C++ exception, in kernel, every > exception must be carefully processed. A simple exception throw may lay > memory leak and unfreed resource allocation. And outer exception catch > is difficult to help inner exception. Even if I have no proof-of-concepts (so maybe somebody can show that this is not fair), if we have setjmp/longjmp in the kernel we can have a correct exception handling mechanism without not great problems. Attilio -- Peace can only be achieved by understanding - A. Einstein
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