Date: Tue, 22 Aug 2000 20:52:54 +0200
From: "Eli Zaretskii" <eliz AT is DOT elta DOT co DOT il>
Sender: halo1 AT zahav DOT net DOT il
To: djgpp AT delorie DOT com
Message-Id: <9628-Tue22Aug2000205253+0300-eliz@is.elta.co.il>
X-Mailer: Emacs 20.6 (via feedmail 8.2.emacs20_6 I) and Blat ver 1.8.5b
In-reply-to: <8nu3ij$9ev2v$2@ID-33463.news.cis.dfn.de>
	(marksmanANTISPAM AT adr DOT dk)
Subject: Re: How do I customize libc for custom OS?
References: <8nqvcn$9a10a$1 AT ID-33463 DOT news DOT cis DOT dfn DOT de> <4331-Mon21Aug2000144127+0300-eliz AT is DOT elta DOT co DOT il> <8nu3ij$9ev2v$2 AT ID-33463 DOT news DOT cis DOT dfn DOT de>
Reply-To: djgpp AT delorie DOT com
Errors-To: nobody AT delorie DOT com
X-Mailing-List: djgpp AT delorie DOT com
X-Unsubscribes-To: listserv AT delorie DOT com
Precedence: bulk

> From: "Tobias Skytte" <marksmanANTISPAM AT adr DOT dk>
> Newsgroups: comp.os.msdos.djgpp
> Date: Tue, 22 Aug 2000 15:01:53 +0200
> 
> ok. whew, looks like alot of work!

You didn't think that porting a large library to a new OS would be a
piece of cake, did you? ;-)

> maybe I could merely change the __dpmi_int and int86 functions?

I doubt that: the functions which call __dpmi_int ``know'' quite a bit
about DOS, its functions, and its idiosyncrasies.  Making them work
with another OS will require more than just replacing __dpmi_int.

For example, the values you load into the registers before calling Int
21h, the error codes you anticipate, and the bugs in the OS that you
work around---all these need changing for a different OS.

> the crt0.S scares me, as I am not that good with assembler (especially not
> att syntax). Is there any documentation available that explains what this
> code does? I have no idea what exactly it does...

See http://www.delorie.com/djgpp/doc/eli-m17n99.html#Startup, I think
it provides some overview of what crt0.S does.  Beyond that, you have
the comments in the code, and you can ask specific questions here.

> Maybe most of it can just be taken out since its mostly for dpmi?
> what would happen if crt0.S contains nothing?

The DPMI-specific parts should be taken out, but you need to replace
them with the equivalent code for your OS.  A program cannot run
unless you set up its data, code, and stack, and build the run-time
environment that a C program expects (the argv[] array, the standard
handles, etc.)