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Date: Mon, 4 Feb 2013 05:05:50 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: H?vard Skinnemoen <hskinnemoen@gmail.com>
Cc: Hans-Christian Egtvedt <egtvedt@samfundet.no>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        David Howells <dhowells@redhat.com>, Dave Jones <davej@redhat.com>,
        Will Deacon <will.deacon@arm.com>,
        Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] arch: avr32: add dummy syscalls
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On Sun, Feb 03, 2013 at 08:52:18PM -0800, H?vard Skinnemoen wrote:

> You're right on -- in this case, the compiler will skip r10, and do
> (r12, r11, r8:r9, stack). We pass the syscall number in r8, but we
> also unconditionally move r7 to r8 in the syscall path, so it
> shouldn't matter (libc does the opposite when necessary).
> 
> I remember some talk about having the compiler reuse r10 for the next
> 32-bit argument in cases like this, but I don't think it ever
> happened.

Umm...  In case of fallocate() the next argument is 64bit one, though;
sys_fallocate() will be looking for two 32bit words on stack, so no
matter how do we pass them to syscall, we'd better push two words in
the wrapper.

But yes, 32bit/32bit/64bit/32bit is another interesting case -
fanotify_mark is 32/32/64/32/32.  From what ABI says it would seem to
be r12/r11/r8:r9/r10/stack, but if I understand you correctly, we'll
end up wanting *two* arguments on stack...