From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mike Haertel <mike@ducky.net>
Message-Id: <200107130626.f6D6QPC01961@ducky.net>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] partial-Plan9ification question
In-Reply-To: <20010713055804.8EB76199C0@mail.cse.psu.edu>
Date: Thu, 12 Jul 2001 23:26:25 -0700
Topicbox-Message-UUID: c9060d38-eac9-11e9-9e20-41e7f4b1d025

>the plan 9 compilers are strictly caller-saves, for all architectures.  other details vary.
>on some platforms, a few useful constants are reserved in floating-point registers.
>
>gcc varies between architectures, and even from platform to platform,
>but i think even on the x86 with hardly any registers, some registers are callee-saved.

On x86 unix systems, eax, edx, and ecx are callee-saves, and the rest
are caller-saves.  eax and edx are used for return values.

For AMD's forthcoming x86-64, the gcc folks actually had the luxury
of being able to invent their own convention, rather than having
to follow a convention dictated to them by existing tools and
libraries.  They did some studies and ended up choosing about half
and half caller and callee saves.  I think there are slightly more
caller-saves registers.  They also went to some effort to pass a
few arguments in registers.  The down side is their conventions
appear hairy.

Just to keep this from drifting off Plan 9 entirely: any luck on
the 8c sign extension bug?