linux-kernel - Re: [PATCH v5 13/25] m68k: add asm/syscall.h

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Date:   Mon, 10 Dec 2018 14:06:28 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     "Dmitry V. Levin" <ldv@...linux.org>
Cc:     Oleg Nesterov <oleg@...hat.com>, Andy Lutomirski <luto@...nel.org>,
        lineprinter@...linux.org, Eugene Syromiatnikov <esyr@...hat.com>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 13/25] m68k: add asm/syscall.h

Hi Dmitry,

On Mon, Dec 10, 2018 at 1:41 PM Dmitry V. Levin <ldv@...linux.org> wrote:
> On Mon, Dec 10, 2018 at 09:45:42AM +0100, Geert Uytterhoeven wrote:
> > On Mon, Dec 10, 2018 at 5:30 AM Dmitry V. Levin <ldv@...linux.org> wrote:
> > > syscall_get_* functions are required to be implemented on all
> > > architectures in order to extend the generic ptrace API with
> > > PTRACE_GET_SYSCALL_INFO request.
> > >
> > > This introduces asm/syscall.h on m68k implementing all 5 syscall_get_*
> > > functions as documented in asm-generic/syscall.h: syscall_get_nr,
> > > syscall_get_arguments, syscall_get_error, syscall_get_return_value,
> > > and syscall_get_arch.
> > >
> > > Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
> > > Cc: Oleg Nesterov <oleg@...hat.com>
> > > Cc: Andy Lutomirski <luto@...nel.org>
> > > Cc: Elvira Khabirova <lineprinter@...linux.org>
> > > Cc: Eugene Syromyatnikov <esyr@...hat.com>
> > > Cc: linux-m68k@...ts.linux-m68k.org
> > > Signed-off-by: Dmitry V. Levin <ldv@...linux.org>
> > > ---
> > >
> > > Notes:
> > >     v5: added syscall_get_nr, syscall_get_arguments, syscall_get_error,
> > >         and syscall_get_return_value
> > >     v1: added syscall_get_arch
> >
> > > --- /dev/null
> > > +++ b/arch/m68k/include/asm/syscall.h
> > > @@ -0,0 +1,39 @@
> >
> > > +static inline void
> > > +syscall_get_arguments(struct task_struct *task, struct pt_regs *regs,
> > > +                     unsigned int i, unsigned int n, unsigned long *args)
> > > +{
> > > +       BUG_ON(i + n > 6);
> >
> > Does this have to crash the kernel?
>
> This is what most of other architectures do, but we could choose
> a softer approach, e.g. use WARN_ON_ONCE instead.
>
> > Perhaps you can return an error code instead?
>
> That would be problematic given the signature of this function
> and the nature of the potential bug which would most likely be a usage error.

Of course to handle that, the function's signature need to be changed.
Changing it has the advantage that the error handling can be done at the
caller, in common code, instead of duplicating it for all
architectures, possibly
leading to different semantics.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds