From owner-freebsd-current@freebsd.org Thu Oct 5 23:13:10 2017 Return-Path: Delivered-To: freebsd-current@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 09066E451AF for ; Thu, 5 Oct 2017 23:13:10 +0000 (UTC) (envelope-from wlosh@bsdimp.com) Received: from mail-io0-x22f.google.com (mail-io0-x22f.google.com [IPv6:2607:f8b0:4001:c06::22f]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id BF70F65DB6 for ; Thu, 5 Oct 2017 23:13:09 +0000 (UTC) (envelope-from wlosh@bsdimp.com) Received: by mail-io0-x22f.google.com with SMTP id m16so6341399iod.1 for ; Thu, 05 Oct 2017 16:13:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bsdimp-com.20150623.gappssmtp.com; s=20150623; h=mime-version:sender:in-reply-to:references:from:date:message-id :subject:to:cc; bh=o4gPzBlPbwbezKasByGTAkq52EDIgVnLx/OaXQjP7bA=; b=bVm93UUGiYdHDFYnyxE5I6UtV7G1g9dSaKP6sMMpv7O9Z7t1MgERpb7ILzPHg3pQQq HgqI6tvADXYbHx3QUecJpX4wEeVqVrzrEqa28Pk4MZlbHdAN6bSSraFLYuETLAUsoH9r +yeC2Yl4wjRjZgtR3WqETk2FbX1dTtgfVpYuoBo+EE0T7EFu4uB1jTZ6/BcWYY5dMraC KjXeDGVc6U1ZfLRyGpkMrYTSG/zBhFqUB5gtV87lhplp/sDjjfLOMtLu/RdnMtPvizyr K66gN0PKV0NMeXX7l2FVYHf5Vhfhx3ozJfGfXKF3fXuLK1pl6ICNMgSy7Ju6D9J0iYhK j/kw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:sender:in-reply-to:references:from :date:message-id:subject:to:cc; bh=o4gPzBlPbwbezKasByGTAkq52EDIgVnLx/OaXQjP7bA=; b=Xr7tDr0me0G3CWxH4vbA+HXNQrlfrPqKc71sbOK7uiFENQS9GHp3LCnF6d6T2mVwjK AZaGqGANxOD/v/AL5JBoGzkqYkJ3/cnFAPESiB+DsGYEF+let/fDuQsdy7HN07dvqpQV eHhljWJGmYYiHsoFBrMgLYjFeuG3EtfEqie8O9TuOiNqbIsgvyxfk++iuoeG9ZUyZxrq kK7VWebCYAaGb0yopX6bm2zKunsSd+qB5KuW7QdKXZXP2qFAHQXjgyxdiR2XNmRCKy1t ye4pooDo3VadcvV81SYh6wwJdfY8AWpyg3OHdfGxDV67PVHvPjh+dz03u5j4qGlGinON yK9w== X-Gm-Message-State: AMCzsaXYdRxcSw2RGdBQE0e9pVAgf2EAjRVPsxFpOgImF5irqAgbrIRk /71SLKrKykrJFHMow94v0ezCxOZ8caWekuVHzASbOQ== X-Google-Smtp-Source: AOwi7QCjvtx5wUMFOMTcb49EIYod2hqkYz28mUsEZCmfTCm563y/cCD8Pirkyasev4dBXhc8d86bD/0Lr3OczNHpJIg= X-Received: by 10.107.185.7 with SMTP id j7mr315188iof.221.1507245189089; Thu, 05 Oct 2017 16:13:09 -0700 (PDT) MIME-Version: 1.0 Sender: wlosh@bsdimp.com Received: by 10.79.94.130 with HTTP; Thu, 5 Oct 2017 16:13:08 -0700 (PDT) X-Originating-IP: [2607:fb10:7021:1::5304] In-Reply-To: References: <1507238672.86205.250.camel@freebsd.org> From: Warner Losh Date: Thu, 5 Oct 2017 16:13:08 -0700 X-Google-Sender-Auth: o1y0hM_hIcDg5tgONdAdjEnqZbU Message-ID: Subject: Re: C++ in jemalloc To: David Goldblatt Cc: Ian Lepore , FreeBSD Current Content-Type: text/plain; charset="UTF-8" X-Content-Filtered-By: Mailman/MimeDel 2.1.23 X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 05 Oct 2017 23:13:10 -0000 Today C++11 is a no-go generally due to the lagging architectures needing gcc 4.2. However, that answer might change soon. Would it be easy for you to avoid C++11, or would that cause you significant pain? And what's the timeline you'd be releasing a new jemalloc requiring this stuff? The answers might change the 'no-go' to 'ok'. Warner On Thu, Oct 5, 2017 at 3:00 PM, David Goldblatt wrote: > So it sounds like C++03 (or rather, the version of C++ supported by g++ > 4.2) will be fine. > > Is C++11 a no-go, without breaking libc on non-Clang architectures? (It > isn't clear to me if having to use the ports gcc to build was unfortunate > or unacceptable from FreeBSD's POV). C++11 would be sort of helpful in the > core implementation (we currently have to maintain our own backport of C11 > atomics, for instance), but would be really helpful in the test suite > (because of how much syntactically simpler it is to, say, spin up a bunch > of threads to hammer a local instance of a data structure). > > - David > > On Thu, Oct 5, 2017 at 2:33 PM, Warner Losh wrote: > >> >> >> On Thu, Oct 5, 2017 at 2:24 PM, Ian Lepore wrote: >> >>> 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). >>> >> >> It's the ubiquity of C++11 is why I didn't just say "Go for it". >> >> Warner >> > >