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[131.111.193.104]) by smtp.gmail.com with ESMTPSA id f23sm16328618wmc.3.2020.09.17.10.23.21 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 17 Sep 2020 10:23:21 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.120.23.2.1\)) Subject: Re: svn commit: r365836 - head/share/mk From: Jessica Clarke In-Reply-To: <202009171705.08HH5CtE014644@gndrsh.dnsmgr.net> Date: Thu, 17 Sep 2020 18:23:19 +0100 Cc: Warner Losh , Alex Richardson , src-committers , svn-src-all , svn-src-head Content-Transfer-Encoding: quoted-printable Message-Id: References: <202009171705.08HH5CtE014644@gndrsh.dnsmgr.net> To: rgrimes@freebsd.org X-Mailer: Apple Mail (2.3608.120.23.2.1) X-Rspamd-Queue-Id: 4BskMJ1pKWz4KZg X-Spamd-Bar: - Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=none; spf=pass (mx1.freebsd.org: domain of jrtc27@jrtc27.com designates 209.85.128.65 as permitted sender) smtp.mailfrom=jrtc27@jrtc27.com X-Spamd-Result: default: False [-1.77 / 15.00]; RCVD_VIA_SMTP_AUTH(0.00)[]; TO_DN_SOME(0.00)[]; MV_CASE(0.50)[]; R_SPF_ALLOW(-0.20)[+ip4:209.85.128.0/17]; RCPT_COUNT_FIVE(0.00)[6]; RCVD_COUNT_THREE(0.00)[3]; NEURAL_HAM_SHORT(-0.27)[-0.271]; FORGED_SENDER(0.30)[jrtc27@freebsd.org,jrtc27@jrtc27.com]; R_DKIM_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; ASN(0.00)[asn:15169, ipnet:209.85.128.0/17, country:US]; MID_RHS_MATCH_FROM(0.00)[]; FROM_NEQ_ENVFROM(0.00)[jrtc27@freebsd.org,jrtc27@jrtc27.com]; ARC_NA(0.00)[]; NEURAL_HAM_MEDIUM(-0.96)[-0.958]; FREEFALL_USER(0.00)[jrtc27]; FROM_HAS_DN(0.00)[]; NEURAL_HAM_LONG(-1.04)[-1.039]; MIME_GOOD(-0.10)[text/plain]; PREVIOUSLY_DELIVERED(0.00)[svn-src-head@freebsd.org]; DMARC_NA(0.00)[freebsd.org]; TO_MATCH_ENVRCPT_SOME(0.00)[]; RCVD_IN_DNSWL_NONE(0.00)[209.85.128.65:from]; RWL_MAILSPIKE_POSSIBLE(0.00)[209.85.128.65:from]; RCVD_TLS_ALL(0.00)[]; MAILMAN_DEST(0.00)[svn-src-head] X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.33 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 17 Sep 2020 17:23:25 -0000 > On 17 Sep 2020, at 18:05, Rodney W. Grimes = wrote: >=20 >> On Thu, Sep 17, 2020 at 9:39 AM Steffen Nurpmeso = wrote: >>=20 >>> Alex Richardson wrote in >>> <202009171507.08HF7Qns080555@repo.freebsd.org>: >>> |Author: arichardson >>> |Date: Thu Sep 17 15:07:25 2020 >>> |New Revision: 365836 >>> |URL: https://svnweb.freebsd.org/changeset/base/365836 >>> | >>> |Log: >>> | Stop using lorder and ranlib when building libraries >>> | >>> | Use of ranlib or lorder is no longer necessary with current = linkers >>> | (probably anything newer than ~1990) and ar's ability to create = an >>> object >>> | index and symbol table in the archive. >>> | Currently the build system uses lorder+tsort to sort the .o files = in >>> | dependency order so that a single-pass linker can use them. = However, >>> | we can use the -s flag to ar to add an index to the .a file which = makes >>> | lorder unnecessary. >>> | Running ar -s is equivalent to running ranlib afterwards, so we = can >>> also >>> | skip the ranlib invocation. >>>=20 >>> That ranlib thing yes (for long indeed), but i have vague memories >>> that the tsort/lorder ordering was also meant to keep the things >>> which heavily interdepend nearby each other. (Luckily Linux >>> always had at least tsort available.) >>> This no longer matters for all the platforms FreeBSD supports? >>>=20 >>=20 >> tsort has no notion of how dependent the modules are, just an order = that >> allows a single pass through the .a file (otherwise you'd need to = list the >> .a file multiple times on the command line absent ranlib). That's the >> original purpose of tsort. tsort, lsort, and ranlib all arrived in = 7th >> edition unix on a PDP-11, where size was more important than = proximity to >> locations (modulo overlays, which this doesn't affect at all). >>=20 >> There were some issues of long vs short jumps on earlier = architectures that >> this helped (since you could only jump 16MB, for example). However, = there >> were workarounds for this issue on those platforms too. And if you = have a >> program that this does make a difference, then you can still use >> tsort/lorder. They are still in the system. >>=20 >> I doubt you could measure a difference here today. I doubt, honestly, = that >> anybody will notice at all. >=20 > The x86 archicture has relative jmps of differning lengths, even in = long mode > there is support for rel8 and rel32. That's irrelevant though for several reasons: 1. The compiler has already decided on what jump instructions to use = based on the requested code model (unless you're on RISC-V and using GNU bfd = ld as that supports linker relaxations that actually delete instruction = bytes). 2. The linker is still free to reorder input sections however it likes, = it doesn't have to follow the order of the input files (and the files = within any archive). 3. If you care about those kinds of optimisations you should use = link-time optimisation which will likely do far more useful things than just = optimise branches, but again isn't constrained by the order of the input = files, it can lay out the code exactly how it wants. Not to mention that this is just a topological sort, not a clustering = sort. Jess