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SubjectRe: [PATCH] arch: avr32: add dummy syscalls
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On Sun, Feb 3, 2013 at 9:05 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> 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.

Right.

> 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...

Yes, I think there may be a difference between the IAR and gcc ABI
here. But I could be wrong.

Havard


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