Date: Thu, 05 Oct 2017 15:24:32 -0600 From: Ian Lepore <ian@freebsd.org> To: Warner Losh <imp@bsdimp.com>, David Goldblatt <davidtgoldblatt@gmail.com> Cc: FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: C++ in jemalloc Message-ID: <1507238672.86205.250.camel@freebsd.org> In-Reply-To: <CANCZdfqO49Jg7vv=mhXZ6-YxqX=C0vSMkR=rnaFdb561hF3XuA@mail.gmail.com> References: <CAHD6eXdazBO4=R7m5odWLt0YyAoTsuZTKvYbEh4_U5ZUXzxt9g@mail.gmail.com> <CANCZdfqO49Jg7vv=mhXZ6-YxqX=C0vSMkR=rnaFdb561hF3XuA@mail.gmail.com>
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On Thu, 2017-10-05 at 14:01 -0700, Warner Losh wrote: > On Thu, Oct 5, 2017 at 11:59 AM, David Goldblatt > wrote: > > > > > Hi all, > > > > The jemalloc developers have wanted to start using C++ for a while, to > > enable some targeted refactorings of code we have trouble maintaining due > > to brittleness or complexity (e.g. moving thousand line macro definitions > > to templates, changing the build->extract symbols->rebuild mangling scheme > > for internal symbols to one using C++ namespaces). We'd been holding off > > because we thought that FreeBSD base all had to compile on GCC 4.2, in > > order to support some esoteric architectures[1]. > > > > The other day though, I noticed that there is some C++ shipping with > > FreeBSD; /usr/bin/dtc and /sbin/devd (the former claiming in the HACKING > > document that C++11 is a minimum for FreeBSD 11). This, combined with the > > fact that ports now points to a modern gcc, makes me think we were > > incorrect, and can turn on C++ without breaking FreeBSD builds. > > > > Am I right? Will anything break if jemalloc needs a C++ compiler to build? > > We will of course not use exceptions, RTTI, global constructors, the C++ > > stdlib, or anything else that might affect C source or link compatibility. > > > > Thanks, > > David (on behalf of the jemalloc developers > > > > [1] That being said, we don't compile or test on those architectures, and > > so probably don't work there in the first place if I'm being honest. But > > we'd also like to avoid making that a permanent state of affairs that can't > > be changed. > > > For FreeBSD 10 and earlier, this would likely break all architectures that > aren't x86. Starting in FreeBSD 11, arm and powerpc are supported by clang, > but not super well. For FreeBSD 12, we're getting close for everything > except sparc64 (whose fate has not yet been finally decided). > > So for the popular architectures, this arrangement might work. For building > with external toolchains, it might also work. Some of the less popular > architectures may be a problem. > > Does that help? It isn't completely cut and dried, but it should be helpful > for you making a decision. > > Warner Wait a sec... we've been compiling C++ code with gcc 4.2 since like 2006. What am I missing here that keeps this answer from being a simple "go for it"? Just stay away from C++11 features and gcc 4.2 should work fine. (DTC may require C++11, but that was likely the author's choice given that there was no requirement for it to work on pre-clang versions of freebsd). -- Ian
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