Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!MCC.COM!herme
From: herme@MCC.COM (Manuel Hermenegildo)
Newsgroups: gnu.emacs
Subject: Re:  shared source question
Message-ID: <8906071437.AA09737@darth.aca.mcc.com>
Date: 7 Jun 89 14:37:32 GMT
References: <8906070331.AA00262@atlantis>
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We have been using a relatively simple method in order to deal with
the problem of having one set of source files and executables for
different machines in an NFS environment. This is a "low tech"
solution that doesn't need any modification of the loader or kernel.
We use it, for example, in a Prolog implementation that uses one set
of source files but runs on many different machines (suns, vaxen, and
multiprocessors -Sequent).  I will describe the method specialized for
emacs, but it is of general application. If you know of a better
method let me know. If you want more info on this one, I will be happy
to provide it.

The first part of the trick is to avoid duplication of source files by
using symbolic links: all versions of emacs can be kept under a common
directory tree.  The top directory in the tree (let's call it
"emacs-dir") contains all the source files (".c" files), a global
Makefile, the directories for the non-machine-specific files --e.g.
lisp source directory--- and a directory called "objcode". In the
objcode directory there are subdirectories for each machine that is
supported (e.g. "sun3", "sun2", "balance", "bobcat", etc.). Each one
of these directories contains >symbolic links< to all the source files
in the "emacs-dir" directory and a specialized copy of the makefile.
Running "make" in each subdirectory in "objcode" creates a
machine-specific version of emacs without duplicating the source
files. Thus, after running make on each "objcode" subdirectory there
will be different machine-specific versions of emacs

....emacs-dir/objcode/sun3/emacs
....emacs-dir/objcode/sun2/emacs
....emacs-dir/objcode/balance/emacs
....emacs-dir/objcode/bobcat/emacs

without having duplicated the source files and libraries. 

The second part of the trick is to select the right executable when
the user types "emacs", depending on which machine he or she is
running on. A simple way to do this is to define at login time (i.e.
in the ".login" file) an environment variable called "hardware" which
contains the type of hardware that the login shell is running on (the
type of hardware can be determined automatically --I can post that
also if someone is interested), and then add to the standard set of
paths a path to the appropriate version of emacs

set path= (....emacs-dir/objcode/$hardware $path)

that way the correct version is selected every time when the user
types "emacs". In general, rather than doing this specifically for
emacs, we organize our "bin" files into subdirectories 

~/bin/sun3
~/bin/sun4
~/bin/balance

which contain links to the right executables for different packages
and set the user path to be  

set path= (~/bin/$hardware $path)

Based on having a correct value in the "$hardware" variable the
creation of the subdirectories (such as "....emacs/objcode/sun4") and
the links to the source files is also automated by using a special
makefile at the top level, so that when you type "make" at the top
level the corresponding "objcode" subdirectory for the machine you are
running on is created (if it didn't exist before), the symbolic links
made, and compilation is automatically started in that subdirectory.
Creating the different versions then simply involves starting shells
on the different machines and typing "make" at the "emacs-dir" level.

Again, I will be happy to provide more info or hear of a better solution.

Manuel Hermenegildo