Re: Bugs (and some fixes)

[David Given <dg@cowlark.com>]

On Monday 12 April 2004 22:31, Tommy McCabe wrote:
> --- Tommy McCabe <rocketjet314@yahoo.com> wrote:
[...]
> > Compiler/memory model limit.
> > If code is...   and data is...  Use this model...
> > under 64KB      under 64KB      Small (-ms) or Tiny
> > (-mt)
> > over 64KB       under 64KB      Medium (-mm)
> > under 64KB      over 64KB       Compact (-mc)
> > over 64KB       over 64KB       Large (-ml)

The way medium and large models manage to get more than 64kB of code is by 
using multiple code segments. Unfortunately, since you can only address 64kB 
with a 16-bit pointer, this means that you have to use wider pointers if you 
want more than 64kB of code. Most compilers use a 32 bit pointer for this; 16 
bits for the segment, 16 bits for the offset. And just to make matters worse, 
medium mode uses *different* sized pointers for code and data!

Probably an easier solution would be to move some kernel subsystems into user 
space. Sockets would be a classic example, since the code's pretty large. 
You'd have to implement a user-mode interface of some description but I doubt 
that would be particularly hard. We'd lose some performance, but seeing as 
we're planning on running this on an 8088, I don't think performance is a 
major design requirement...

-- 
+- David Given --McQ-+ "I smell a rat; I see him forming in the air &
|  dg@cowlark.com    | darkening the sky; but I'll nip him in the bud."
| (dg@tao-group.com) | --- Sir Boyle Roche
+- www.cowlark.com --+