From: jbs30000 AT aol DOT com (Joel)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Quick and Easy DJGPP extended inline assembly question.
Date: 23 Jul 2003 17:12:54 -0700
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DJ Delorie <dj AT delorie DOT com> wrote in message news:<200307231241 DOT h6NCfbvk000773 AT envy DOT delorie DOT com>...
> > __asm__ __volatile__(
> > "movw %w0, %%fs\n"
> > ".byte 0x64 \n"
> > "movb %b1, (%k2)"
> > :
> > : "rm" (selector), "qi" (value), "r" (offset));
> > }
>  
> > Looking at the "rm" (selector) and "movw %w0, %%fs" parts, I assume
> > that this allows selector to be placed directly into the fs register,
> > right?
> 
> Yes.  It can be copied from a register ("r") or an immediate value can
> be used ("i").
> 
> > Also, "qi" (value) moves value directly into al?
> 
> "value" gets put into either al, bl, cl, dl ("q"), or an immediate
> value can be used ("i").
> 
> "offset" is put into any 16-bit register (ax, bx, si, etc) ("r").
> 
> In both cases, the compiler will use whatever selection is optimal for
> the program.
> 
> The "b" in "%b1" means it's a byte.  The "k" in "%k2" means it's a
> dword (4 bytes).
Yeah, I knew about the "b" and "k" but I didn't know about combining
constraints, like ri and qi to allow an either/or situation.  That's a
good thing to know, thanks.