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Date: Sun, 27 Jan 2013 20:30:09 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Hans-Christian Egtvedt <egtvedt@samfundet.no>
Cc: Matthias Brugger <matthias.bgg@gmail.com>,
        Haavard Skinnemoen <hskinnemoen@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@vger.kernel.org
Subject: Re: [PATCH] arch: avr32: add dummy syscalls
Message-ID: <20130127203009.GG4503@ZenIV.linux.org.uk>
References: <1359291015-4544-1-git-send-email-matthias.bgg@gmail.com>
 <20130127195714.GA11224@samfundet.no>
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On Sun, Jan 27, 2013 at 08:57:14PM +0100, Hans-Christian Egtvedt wrote:
> Around Sun 27 Jan 2013 13:50:15 +0100 or thereabout, Matthias Brugger wrote:
> > This patch adds dummy syscalls so that compiling
> > for this architecture does not provoke warnings when
> > checksyscalls.sh is called.
> 
> Does any of these syscalls take more than 5 arguments? If so, it is also
> needed to do some stack handling. I would rather not add syscalls that cause
> the kernel to misbehave.

BTW, it might make sense to teach SYSCALL_DEFINE6 to generate such a wrapper
on avr32.  How about something along the lines of
* SYSCALL_DEFINE6(foo, ...) generating (via asm volatile, right next to
sys_foo())
__sys_##foo:
        pushm   lr
        st.w    --sp, r3
	call	sys_##foo
        sub     sp, -4
        popm    pc
* SYSCALL_DEFINE[0..5](foo, ...) generating
	SYSCALL_ALIAS(__sys_foo, sys_foo)
* syscall_table.S beginning with
        .section .rodata,"a",@progbits
        .type   sys_call_table,@object
        .global sys_call_table
        .align  2
#define SYS(name) __sys_##name
sys_call_table:
        SYS(restart_syscall)
	SYS(exit)
	SYS(fork)
	...

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.