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To: linux-kernel@vger.kernel.org
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH -mm] i386 syscall opcode reordering (pipelining)
Date: Tue, 13 Jun 2006 15:21:27 -0700 (PDT)
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Followup to:  <e6nd68$4sq$1@terminus.zytor.com>
By author:    "H. Peter Anvin" <hpa@zytor.com>
In newsgroup: linux.dev.kernel
> 
> Probably not.  The _syscallN() macros are broken for the general case
> on any 32-bit architecture, since they can't handle multiregister
> arguments.
> 
> Similarly, a general syscall() function is broken (in the sense that
> one would have to have syscall-specific code to mangle the arguments)
> on *some*, but not all, 32-bit architectures, since some architectures
> have alignment constraints on multiregister arguments, and the syscall
> number argument throws off that alignment.
> 

I should probably add that it is possible to write _syscallN() macros
that handle multiregister arguments correctly; just the current ones
aren't done correctly.  The complexity gets pretty staggering for the
higher argument counts, though, as for each _syscallN() you have to
support 2^N possible cases, just to deal with 32- and 64-bit arguments
(which is all we support at this point, so it'd be okay.)

	-hpa