linux-kernel - Re: [PATCH] arch: avr32: add dummy syscalls

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Message-ID: <20130204003047.GW4503@ZenIV.linux.org.uk>
Date:	Mon, 4 Feb 2013 00:30:47 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Hans-Christian Egtvedt <egtvedt@...fundet.no>
Cc:	Matthias Brugger <matthias.bgg@...il.com>,
	Haavard Skinnemoen <hskinnemoen@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Dave Jones <davej@...hat.com>,
	Will Deacon <will.deacon@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arch: avr32: add dummy syscalls

On Mon, Feb 04, 2013 at 12:10:55AM +0000, Al Viro wrote:
> On Sun, Jan 27, 2013 at 09:39:54PM +0100, Hans-Christian Egtvedt wrote:
> > > If you are OK with going that way, I could probably put together patches doing
> > > just that.  Note that for rt_sigsuspend/rt_sigreturn/sigaltstack the wrappers
> > > are not needed at all - they can just use current_pt_regs() in syscall body.
> > > IOW, all of syscall-stubs.S could be killed.
> > 
> > Nice, could you put together the preprocessor stuff in a patch? It would be
> > great to not having to write a re-occuring stub for each syscall that has 6+
> > arguments.
> > 
> > Thanks for looking at this.
> 
> Apologies about the delay...  One question: what's the AVR32 C ABI for
> passing 64bit arguments?  The tricky bugger is sys_sync_file_range();
> it takes (s32, s64, s64, u32) as arguments and if not any pair of
> registers can be used to pass 64bit value, we have more serious trouble
> there...

BTW, it's worse: both fadivse64 and fadvise64_64 are wired, neither of them
has a wrapper and arguments are (s32, s64, u32, s32) and (s32, s64, s64, s32)
resp.  The former is OK unless you have restrictions on register pairs that
can be used for 64bit; the latter is past the 5-register limit no matter what,
so the wrapper is really needed.
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