svn commit: r365836 - head/share/mk

[Warner Losh]

On Thu, Sep 17, 2020 at 9:39 AM Steffen Nurpmeso <steffen at sdaoden.eu> wrote:

> Alex Richardson wrote in
>  <202009171507.08HF7Qns080555 at 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.

Warner