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    SubjectRe: [PATCH 02/15] arm: __NR_syscalls fix
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    On Wed, Apr 23, 2014 at 12:27 PM, Russell King - ARM Linux
    <linux@arm.linux.org.uk> wrote:
    > 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.

    All I can say is: UGGGGH.

    But I've not had close encounters with arch code, so this may be
    acceptable to you. Whatever...

    Thanks,
    Miklos


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