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

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Date:	Fri, 11 Apr 2014 12:54:21 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Miklos Szeredi <miklos@...redi.hu>
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 01:50:50PM +0200, Miklos Szeredi wrote:
> On Fri, Apr 11, 2014 at 12:33 PM, Russell King - ARM Linux
> <linux@....linux.org.uk> wrote:
> > On Fri, Apr 11, 2014 at 12:25:38PM +0200, Miklos Szeredi wrote:
> >> From: Miklos Szeredi <mszeredi@...e.cz>
> >>
> >> Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
> >> Cc: Russell King <linux@....linux.org.uk>
> >> ---
> >
> > This has me wondering...
> >
> > (a) what you think it fixes
> > (b) whether you tried to build-test this
> >
> > The ARM instruction set supports 8-bit immediate constants with an even
> > power of two shift.  384 fits that (0x180), 382 does not (0x17e), and
> > in your following patch, 383 definitely doesn't (0x17f).
> >
> > Having this constant larger than necessary does not cause any problem
> > for the syscall table: we explicitly pad it with calls to sys_ni_syscall
> > to make up the difference.
> 
> 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.

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