linux-kernel - Re: [PATCH 02/15] arm: __NR

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Date:	Fri, 11 Apr 2014 13:45:02 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Miklos Szeredi <miklos@...redi.hu>,
	Wade Farnsworth <wade_farnsworth@...tor.com>,
	Al Viro <viro@...iv.linux.org.uk>
Cc:	linux-arch <linux-arch@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Miklos Szeredi <mszeredi@...e.cz>
Subject: Re: [PATCH 02/15] arm: __NR_syscalls fix

On Fri, Apr 11, 2014 at 02:02:32PM +0200, Miklos Szeredi wrote:
> On Fri, Apr 11, 2014 at 1:54 PM, Russell King - ARM Linux
> <linux@....linux.org.uk> wrote:
> > On Fri, Apr 11, 2014 at 01:50:50PM +0200, Miklos Szeredi wrote:
> >> Yes, and the padding will be of wrong length if NR_syscalls is
> >> incorrect (which may be Oopsable?).  At least that is my impression
> >> from a casual glance.
> >
> > Please explain.
> 
> Look at ending lines of arch/arm/kernel/calls.S: if  NR_syscalls is a
> multiple of 4, then syscalls_padding will be zero.  I.e. no padding
> despite the fact that there is in fact only 382 system calls in table
> and there should be 2 sys_ni_syscall pads.

Hmm, it looks like you're right... this used to work fine until...

commit 1f66e06fb6414732bef7bf4a071ef76a837badec
Author: Wade Farnsworth <wade_farnsworth@...tor.com>
Date:   Fri Sep 7 18:18:25 2012 +0100

    ARM: 7524/1: support syscall tracing

because the tracing code wanted to know the number of syscalls.  I don't
know what the answer is here, because the current solution is IMHO far
to fragile.

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