Re: [PATCH] arch: avr32: add dummy syscalls

[Al Viro <viro@ZenIV.linux.org.uk>]

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...