Date: Mon, 2 Nov 1998 15:51:16 +0200 (IST)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
X-Sender: eliz AT is
To: Christian Hofrichter <ChristianHofrichter AT gmx DOT de>
cc: djgpp AT delorie DOT com
Subject: Re: Neeed some help about protected-mode-memory-management
In-Reply-To: <363D8E66.CD0DDE3D@gmx.de>
Message-ID: <Pine.SUN.3.91.981102153916.12647E-100000@is>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Reply-To: djgpp AT delorie DOT com

Please note that usually it is best not to ask too many different 
questions in a single longish message.

On Mon, 2 Nov 1998, Christian Hofrichter wrote:

> How can I get the offset of a variable or a function ?
> 
>             offset=&variable;

Yes.

>             offset=function  or  offset=&function

Any one will do.

> How can I get the size of a function ?

In general, you can't.  If you need this, write your function in 
assembly.

There's a trick of putting two dummy functions before and after the one 
whose size you need, and subtracting the addresses to get the size.  But 
this isn't guaranteed to work, although with present versions of the 
compiler it does work.

> Why do I have to lock the memory when I want to access a linear address
> ? I mean when this space is swaped to disk and I want to access it with
> a selector and an offset, doesn't the dpmi-server reload it from disk
> automaticly ?

It does, and you don't have to lock it, unless you touch it inside an 
interrupt handler.  Paging from within an interrupt handler is not 
allowed, see section 18.11 of the DJGPP FAQ list for details about this.

> When I want to copy memory-blocks in the space above 1 MB (in
> assembler), is this the same procedure like in real-mode with the
> difference that I have to store the selectors in the registers where I
> had to store the segments in the real-mode before ?

I don't understand the question.  In protected mode, segments and 
selectors are the same (more precisely, you can only refer to a segment 
by its selector).  So the answer is yes and no.

And besides, you can use memcpy to copy blocks rather than reinvent the 
wheel in assembly.

> Can I have direct access to memory in the space above1 MB  without using
> the FAT DS method ?

Not clear enough, since your program's variables are all above 1MB and 
you have direct access to them.

If you mean direct access to absolute addresses (like to memory-mapped 
peripheral devices), then the answer is no; you need to use one of the 
methods described in section 18.4 of the FAQ.  FAT DS is one of them, but 
by no means the recommended one.

> Can I have direct access to memory in the space under 1 MB  without
> using the FAT DS method ?

Same as above.

> When I map linear memory, what does it mean ?

Please explain what function do you use to ``map linear memory''.  The 
answer depends on that.

> How can I get the physical address when I have a selector and an offset
> (this memory-space is not swaped to disk) ?

You can't get the physical address without messing with the descriptor 
tables (which is DPMI server-dependent, and usually very hard).

> Do the memory-copy-routines - for the protected-mode in Djgpp- move 4
> bytes at one time ?

Yes.  (You could look in the sources, btw.)