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To: linux-kernel@vger.kernel.org
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: Where is it written?
Date: 11 Nov 2000 15:30:43 -0800
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In-Reply-To: <20001110184031.A2704@munchkin.spectacle-pond.org> <20001110192751.A2766@munchkin.spectacle-pond.org> <20001111163204.B6367@inspiron.suse.de> <20001111171749.A32100@wire.cadcamlab.org>
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Followup to:  <20001111171749.A32100@wire.cadcamlab.org>
By author:    Peter Samuelson <peter@cadcamlab.org>
In newsgroup: linux.dev.kernel
> 
> [Andrea Arcangeli]
> > Can you think at one case where it's better to push the parameter on
> > the stack instead of passing them through the callee clobbered
> > ebx/eax/edx?
> 
> Well it's safer if you are lazy about prototyping varargs functions.
> But of course by doing that you're treading on thin ice anyway, in
> terms of type promotion and portability.  So I guess it's much better
> to say "varargs functions MUST be prototyped" and use the registers.
> 

It definitely is now.  At the time the original x86 ABI was created, a
lot of C code was still K&R, and thus prototypes didn't exist...

> 
> AIUI gcc can cope OK with multiple ABIs to be chosen at runtime, am I
> right?  IRIX, HP-UX and AIX all have both 32-bit and 64-bit ABIs.
> 

I don't think we want to introduce a new ABI in user space at this
time.  If we ever have to major-rev the ABI (libc.so.7), then we
should consider this.

	-hpa
-- 
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!
"Unix gives you enough rope to shoot yourself in the foot."
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