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

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Date:	Sun, 27 Jan 2013 20:30:09 +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 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.
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