This section explains the steps involved in building the Emacs executable. You don't have to know this material to build and install Emacs, since the makefiles do all these things automatically. This information is pertinent to Emacs maintenance.
Compilation of the C source files in the `src' directory produces an executable file called `temacs', also called a bare impure Emacs. It contains the Emacs Lisp interpreter and I/O routines, but not the editing commands.
The command `temacs -l loadup' uses `temacs' to create the real runnable Emacs executable. These arguments direct `temacs' to evaluate the Lisp files specified in the file `loadup.el'. These files set up the normal Emacs editing environment, resulting in an Emacs that is still impure but no longer bare.
It takes a substantial time to load the standard Lisp files. Luckily, you don't have to do this each time you run Emacs; `temacs' can dump out an executable program called `emacs' that has these files preloaded. `emacs' starts more quickly because it does not need to load the files. This is the Emacs executable that is normally installed.
To create `emacs', use the command `temacs -batch -l loadup dump'. The purpose of `-batch' here is to prevent `temacs' from trying to initialize any of its data on the terminal; this ensures that the tables of terminal information are empty in the dumped Emacs. The argument `dump' tells `loadup.el' to dump a new executable named `emacs'.
Some operating systems don't support dumping. On those systems, you must start Emacs with the `temacs -l loadup' command each time you use it. This takes a substantial time, but since you need to start Emacs once a day at most--or once a week if you never log out--the extra time is not too severe a problem.
You can specify additional files to preload by writing a library named
`site-load.el' that loads them. You may need to increase the value
of PURESIZE, in `src/puresize.h', to make room for the
additional data. (Try adding increments of 20000 until it is big
enough.) However, the advantage of preloading additional files
decreases as machines get faster. On modern machines, it is usually not
advisable.
After `loadup.el' reads `site-load.el', it finds the
documentation strings for primitive and preloaded functions (and
variables) in the file `etc/DOC' where they are stored, by calling
Snarf-documentation (see section Access to Documentation Strings).
You can specify other Lisp expressions to execute just before dumping by putting them in a library named `site-init.el'. This file is executed after the documentation strings are found.
If you want to preload function or variable definitions, there are three ways you can do this and make their documentation strings accessible when you subsequently run Emacs:
nil value for
byte-compile-dynamic-docstrings as a local variable in each these
files, and load them with either `site-load.el' or
`site-init.el'. (This method has the drawback that the
documentation strings take up space in Emacs all the time.)
It is not advisable to put anything in `site-load.el' or `site-init.el' that would alter any of the features that users expect in an ordinary unmodified Emacs. If you feel you must override normal features for your site, do it with `default.el', so that users can override your changes if they wish. See section Summary: Sequence of Actions at Start Up.
If you want to use this function in an Emacs that was already dumped, you must run Emacs with `-batch'.
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