Date: Tue, 15 Nov 94 19:13:42 GMT
From: dolan AT fnoc DOT navy DOT mil (Kent Dolan)
To: djgpp AT sun DOT soe DOT clarkson DOT edu
Subject: scatter loading executables

Subject: Re: Shared libraries
Mailer: VM 5.32 (beta) for GNU Emacs 18.59.5

??> Why not build something like that into DJGPP 2.0?  Have the stub launch a
??> loader which exits after loading the libraries?

DJ> There's still the problem of where to put the library.  Most systems
DJ> that support shared libraries can load the library at a predictable
DJ> address, so that no relocation is needed.  In DPMI 0.9, there is no
DJ> way of doing this.

> Dong Liu  <dliu AT ace DOT njit DOT edu>

DL> The linux a.out shared libraries use fixed addresses, it is a pain to
DL> make and maintain this kind libraries. It uses a specially hacked
DL> version "as". With PIC code, it is much easier. Is it possible for two
DL> tasks sharing pages in DJGPP 2.0? If it is, the dynamic loader and
DL> shared libraries can be loaded in to memory by the first go32 program,
DL> the spwaned task doesn't need to read them from disk again. That mus
DL> save a lot of memory and time.(especially programs use libg++).

Might be worth taking a look at how the Amiga does it.  Code is
compiled or assembled or whatever into "hunks" which are then scatter
loaded into memory, I suppose with long jumps resolved at load time
from one hunk to another.  It wouldn't be that awful a thing, with
virtual memory, to have a program loaded in dll hunks with holes
between, if each hunk were built to start on a page boundary and unused
holes took up no physical memory.  You'd lose some memory to
fragmentation, but gain the benefits of dll.

The real stinger is that a benefit of dlls is supposed to be the
ability to replace library elements without relinking the main
program.  If the linking of the main program has to know how much room
to allow for each of the dll modules, this won't work any more.

Xanthian.
--
Kent, the man from xanth.
Kent Paul Dolan, CSC contractor at Fleet Numerical.  (408) 656-4363.
(Navy Unix email:   )  (Navy cc:Mail email: )  (real world email:     )
<dolan AT fnoc DOT navy DOT mil>  <dolank AT fnoc DOT navy DOT mil>  <xanthian AT well DOT sf DOT ca DOT us>