linux-kernel - Re: [PATCH v2 3/4] input: Deprecate real timestamps beyond year 2106

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Message-ID: <1563780.JF7NgVgytb@wuerfel>
Date:   Sat, 29 Oct 2016 00:01:14 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Deepa Dinamani <deepa.kernel@...il.com>,
        "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        y2038 Mailman List <y2038@...ts.linaro.org>
Subject: Re: [PATCH v2 3/4] input: Deprecate real timestamps beyond year 2106

On Friday, October 28, 2016 2:56:10 PM CEST Dmitry Torokhov wrote:
> On Fri, Oct 28, 2016 at 2:47 PM, Arnd Bergmann <arnd@...db.de> wrote:
> > On Friday, October 28, 2016 2:39:35 PM CEST Deepa Dinamani wrote:
> >> >> >> @@ -55,24 +60,24 @@ struct ff_effect_compat {
> >> >> >>
> >> >> >>  static inline size_t input_event_size(void)
> >> >> >>  {
> >> >> >> -       return (in_compat_syscall() && !COMPAT_USE_64BIT_TIME) ?
> >> >> >> -               sizeof(struct input_event_compat) : sizeof(struct input_event);
> >> >> >> +       return in_compat_syscall() ? sizeof(struct raw_input_event_compat) :
> >> >> >> +                                    sizeof(struct raw_input_event);
> >> >> >>  }
> >> >> >
> >> >> > I think the COMPAT_USE_64BIT_TIME check has to stay here,
> >> >> > it's needed for x32 mode on x86-64.
> >> >>
> >
> > We have to distinguish four cases on x86:
> >
> > - native 32-bit, input_event with 32-bit time_t
> > - compat 32-bit, input_event_compat with 32-bit time_t
> > - native 64-bit, input_event with 64-bit time_t
> > - compat x32, input_event with 64-bit time_t
> >
> > The first three can happen on other architectures too,
> > the last one is x86 specific. There are probably other ways
> > to express the condition above, but I can't think of one
> > that is better than the one we have today.
> 
> Can we detect if given task is compat x32, like we do for compat
> 64/32? Or entire userspace has to be x32?

Yes, this works fine per task, with the definition of COMPAT_USE_64BIT_TIME
that is hardcoded to zero everywhere except on x86 where it is

#define COMPAT_USE_64BIT_TIME \
        (!!(task_pt_regs(current)->orig_ax & __X32_SYSCALL_BIT))

This is unrelated to the patch in question, the existing code
is correct as long as we don't change the logic and just
replace input_event with raw_input_event (or __kernel_input_event
or whichever you prefer).

	Arnd