Newsgroups: comp.os.msdos.djgpp
From: frenchc AT cadvision DOT com (Calvin French)
Subject: Re: Calling NASM-compiled functions
References: <357c22f5 DOT 911179 AT news DOT esoterica DOT pt>
Date: Tue, 09 Jun 1998 10:12:02 GMT
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Organization: CADVision Development Corporation (http://www.cadvision.com/)
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To: djgpp AT delorie DOT com
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>I looked through the FAQ but didn't find any help for this problem:

look for djgppasm document, it will probably be very useful to you.

>I would like to use a function which is compiled with NASM (and runs
>OK) and have its parameters redirected to registers, such as this code
>(WATCOM C/C++):
>
>void func(long a, long b);
>#pragma aux func "*" parm [esi] [edi]
>
>this means a goes into the ESI register and b goes into EDI, and i can
>use them in the assembly code.
>
>Is there a way to do this in DJGPP without having to resort to
>externally-declared variables, such as i'm doing now?
>
>a = 1;
>b = 1;
>func();
>
>this looks dirty.

it is. normally with variables you pass in func( a, b ), for instance, a and 
b are placed on the stack and then func() is called. so from inside your 
function you normally do:

_myfunc:
push ebp        ; save ebp b/c you have to
mov ebp, esp    ; set up what is called "stack frame"
mov esi,[ebp+8] ; I *think* 8 is right, for a.
mov edi,[ebp+12] ; ditto, but again i could be off by 4 (or more) or also have 
                        ; them backwards
pop ebp
ret

That's how it happens, I'm not sure what's up with that watcom thing, but 
djgpp does have a similar convention for inlining asm, but you probaly don't 
want to go there with me (I'm pretty helpless when it comes to the normal 
djgpp assembler, I don't use inline asm except what other people write, hehe)

Cheers,

- Calvin -

---

http://www.cadvision.com/frenchc/                  (Wig out, peeps.)
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