Re: C++ in jemalloc

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