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From: ld AT jasmine DOT netrix DOT com (Long Doan)
Subject: Re: Wrapper functions??
Lines: 45
Sender: root AT netrix DOT com
Organization: Netrix Corporation
References: <45mo1g$eth AT nic-nac DOT CSU DOT net>
Date: Mon, 16 Oct 1995 17:15:24 GMT
To: djgpp AT sun DOT soe DOT clarkson DOT edu
Dj-Gateway: from newsgroup comp.os.msdos.djgpp

In article <45mo1g$eth AT nic-nac DOT CSU DOT net> svincent AT zippy DOT sonoma DOT edu (Sam Vincent) writes:

> Hi all,
> 
> What exactly do the interrupt handling wrapper functions do...
> I've been told they take a large chunk of runtime to process and
> that I should write my own assembly functions..  Well Ive done that
> and I save/restore eax, ebx, ecx, and edx and a iret at the end...

[snip]

The wrapper functions do the following:
1. When the ..._alocate_wrapper_... functions are called, they'll:
   a. Write necessary values (%ds, stack, etc) to the wrapper.
   b. (Future, v2.xxx+) lock some of your handler's code, stack, etc.
2. Save ALL registers (%e[abcd]x, %esi, %edi, [defg]s)
3. Switch to a (probably locked) new stack.
4. Set %[defg]s to known value. This value is taken from step 1.
5. Call the given function.
6. Restore all registers to their original values.
7. iret.

If you want to write a handler that doesn't need a wrapper, you
should:

1. Lock the function's code and possibly data.
2. (Optional) Alocate and lock a small stack.
3. In the handler itself, do the following:
   a. Save only the necessary registers.
   b. (Optional) Switch stack.
   b. If you need to access the program's data, set %ds to your
      program's %ds.
   .....
   c. Restore the modified regiters.
   d. iret.

Hope that helps,
Long.
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Long Doan                                        ld AT netrix DOT com     
Netrix Corporation                         ldoan1 AT osf1 DOT gmu DOT edu
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