Path: utzoo!attcan!cmtl01!matrox!uvm-gen!uunet!lll-winken!ames!mailrus!tut.cis.ohio-state.edu!rutgers!paul.rutgers.edu!chain
From: chain@paul.rutgers.edu (Chain Lee)
Newsgroups: comp.os.minix
Subject: Using shared library in minix/PC
Keywords: minix,library,shared
Message-ID: <Jan.26.01.02.38.1989.16320@paul.rutgers.edu>
Date: 26 Jan 89 06:02:38 GMT
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 34


I am suggesting that we use shared library subroutines in PC version 
of minix. This can be justified by the following advantages.
	1. Instead of having copies of same library subroutine in 
every executable disk file, and in every code segment of processes, 
we can put only a single copy in the kernel (or a process served as 
shared library host), to be called by all processes using it.
This will save disk and especially memory space in a PC minix where 
there is a 64K/code limitation. Larger programs s.a. fully functioned
kermit can be made able to run and, # processes that can run at the same
time can be increased. It may also be able to make the future window
manager more usable.
	2. Whenever a change is made on a subroutine, there is no
need to recompile the entire system software, instead, only the kernel
needs to be rebuilt. 
	3. There is no compatibility problem. Commands compiled under
original system can still run under the system with shared library.

Although shared codes usually need address translation hardware to
support, shared library subroutines can be implemented in 8088
or 286/386 real mode in software. e.g. a software interrupt
instruction can be used to call  a shared subroutine, as we did to a 
system call. The problem is to decide which subroutine is to be 
present in the shared library and which is not, such that the system 
can benefit the most (the kernel is not too large but commonly used 
subroutines will be present). Candidates may include C runtime, curses, 
and probably the ones found in runtime library of the window manager 
which we are expecting.
The only disadvantage is that a few more instructions need to be 
executed for each shared subroutine call. But if most of the 
subroutines we chosed are long enough, the negative effect can be
neglected.

Chain Lee