Date: Thu, 17 Sep 2020 18:22:39 +0100 From: Alexander Richardson <arichardson@freebsd.org> To: rgrimes@freebsd.org Cc: Warner Losh <imp@bsdimp.com>, src-committers <src-committers@freebsd.org>, svn-src-all <svn-src-all@freebsd.org>, svn-src-head <svn-src-head@freebsd.org> Subject: Re: svn commit: r365836 - head/share/mk Message-ID: <CA%2BZ_v8reonS-euCGxyAhp1R1N%2BP62gJSjMa-kPJAfamvf%2BGuvQ@mail.gmail.com> In-Reply-To: <202009171705.08HH5CtE014644@gndrsh.dnsmgr.net> References: <CANCZdfqUZRPbbZRsEvVa_rdx0%2BYou9LVihatKZSTTdouaRzKWQ@mail.gmail.com> <202009171705.08HH5CtE014644@gndrsh.dnsmgr.net>
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On Thu, 17 Sep 2020 at 18:05, Rodney W. Grimes <freebsd@gndrsh.dnsmgr.net> wrote: > > > On Thu, Sep 17, 2020 at 9:39 AM Steffen Nurpmeso <steffen@sdaoden.eu> wrote: > > > > > 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. > > > > > > 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? > > > > > > > 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). > > > > 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. > > > > I doubt you could measure a difference here today. I doubt, honestly, that > > anybody will notice at all. > > The x86 archicture has relative jmps of differning lengths, even in long mode > there is support for rel8 and rel32. However, unless you have linker relaxations (e.g. RISC-V) the compiler has to emit the large size anyway since the linker won't replace a 32-bit immediate with an 8-bit one since that changes all later offsets. Alex
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