linux-kernel - Re: [PATCH 7/3] signal: Deliver all of the perf_data in si

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Date:   Sun, 2 May 2021 21:13:34 +0200
From:   Marco Elver <elver@...gle.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Florian Weimer <fweimer@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Collingbourne <pcc@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        sparclinux <sparclinux@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [PATCH 7/3] signal: Deliver all of the perf_data in si_perf

On Sun, 2 May 2021 at 20:39, Eric W. Biederman <ebiederm@...ssion.com> wrote:
>
> Marco Elver <elver@...gle.com> writes:
>
> > On Sat, 1 May 2021 at 01:44, Eric W. Biederman <ebiederm@...ssion.com> wrote:
> >>
> >> Don't abuse si_errno and deliver all of the perf data in si_perf.
> >>
> >> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> >> ---
> >
> > Thank you for the fix, this looks cleaner.
> >
> > Just note that this patch needs to include updates to
> > tools/testing/selftests/perf_events. This should do it:
> >>  sed -i 's/si_perf/si_perf.data/g; s/si_errno/si_perf.type/g' tools/testing/selftests/perf_events/*.c
> >
> > Subject: s/perf_data/perf data/ ?
> >
> > For uapi, need to switch to __u32, see below.
>
> Good point.
>
> The one thing that this doesn't do is give you a 64bit field
> on 32bit architectures.
>
> On 32bit builds the layout is:
>
>         int si_signo;
>         int si_errno;
>         int si_code;
>         void __user *_addr;
>
> So I believe if the first 3 fields were moved into the _sifields union
> si_perf could define a 64bit field as it's first member and it would not
> break anything else.
>
> Given that the data field is 64bit that seems desirable.

Yes, it's quite unfortunate -- it was __u64 at first, but then we
noticed it broke 32-bit architectures like arm:
https://lore.kernel.org/linux-arch/20210422191823.79012-1-elver@google.com/

Thanks,
-- Marco