From: utzoo!decvax!harpo!seismo!rlgvax!guy
Newsgroups: net.unix-wizards
Title: Re: printf(3) as a system call?
Article-I.D.: rlgvax.207
Posted: Sat Apr  9 00:16:31 1983
Received: Sun Apr 10 01:05:20 1983
References: ariel.276 unc.4910

printf should probably not be a system call, because things should
only be system calls if: 1) it requires kernel privileges, 2) you
get a significant performance improvement, or 3) the code *really*
wants access to kernel data structures and becomes massively kludgy
if it has to run in user mode.  The better way to handle "printf" is
to implement shared libraries in UNIX, but shared libraries are a pain
in the neck (the code would either have to have its references to external
data resolved by the "exec" system call or would have to reference all
such data through an indirect pointer).  The 16032 has a "module table"
and a "module pointer" register like the stack and frame pointers, which
points to a given object module's static/global data, which solves 90%
of the problem (the other 10% is references by a routine in a library
to a user-supplied routine or global area).

A *lot* of operating systems seem to have the idea that anything that
could be considered a service routine for user code belongs as a system
call; things like printf, ctime, etc.  The "real" solution, of course, is
to have a domain-oriented protection system (or *no* protection system,
like Xerox's Pilot OS), and make all system calls library routines!
Of course, this works only with the right hardware...

					Guy Harris
					RLG Corporation
					{seismo,mcnc,we13}!rlgvax!guy