linux-kernel - Re: [PATCH] Common compat_sys

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Message-ID: <20070107151817.GN24620@parisc-linux.org>
Date:	Sun, 7 Jan 2007 08:18:17 -0700
From:	Matthew Wilcox <matthew@....cx>
To:	Christoph Hellwig <hch@...radead.org>,
	Kyle McMartin <kyle@...isc-linux.org>, akpm@...l.org,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	parisc-linux@...ts.parisc-linux.org
Subject: Re: [PATCH] Common compat_sys_sysinfo

On Sun, Jan 07, 2007 at 03:13:19PM +0000, Christoph Hellwig wrote:
> and last but not least we probably want a unified mechanisms to deal
> with the 64bit arguments that are broken up into two 32bit ones (not just
> for emulation but also for 32it BE architectures)

It's not BE that is the problem -- drepper thought of that.

What he fundamentally missed was the calling convention where 64-bit
arguments have to be 64-bit aligned, even when they're passed through
registers.  So:

int foo(int, long long);

takes its arguments in arg0, arg2 and arg3, but glibc passes the syscall
arguments in arg0, arg1 and arg2.

I think the Right Way to fix this is for some gcc hacker to implement an
__attribute__((packed_args)) that changes the calling convention for
that function, then we can define asmlinkage to use that on mips and
parisc.

Any budding gcc hackers out there?  ;-)
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