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SubjectRe: [PATCH 02/15] arm: __NR_syscalls fix
On Fri, Apr 11, 2014 at 01:45:02PM +0100, Russell King - ARM Linux wrote:
> 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@arm.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@mentor.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.

Actually, no, you're wrong. Look closely at the definitions. __NR_syscalls
is not the same as NR_syscalls.

__NR_syscalls is the statically defined size of the syscall table for
*probes purposes.

NR_syscalls is the assembly-counted number of CALL() macros in
arch/arm/kernel/calls.S.

So, patch 2 isn't required, and patch 3 needs to be fixed up to take
this into account...

--
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improving, and getting towards what was expected from it.


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