linux-kernel - Re: [PATCH v3 00/12] signal: sort out si_trapno and si

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Message-ID: <CAMuHMdUXh45iNmzrqqQc1kwD_OELHpujpst1BTMXDYTe7vKSCg@mail.gmail.com>
Date:   Thu, 6 May 2021 09:00:59 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Marco Elver <elver@...gle.com>, 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 v3 00/12] signal: sort out si_trapno and si_perf

Hi Eric,

On Tue, May 4, 2021 at 11:14 PM Eric W. Biederman <ebiederm@...ssion.com> wrote:
> This set of changes sorts out the ABI issues with SIGTRAP TRAP_PERF, and
> hopefully will can get merged before any userspace code starts using the
> new ABI.
>
> The big ideas are:
> - Placing the asserts first to prevent unexpected ABI changes
> - si_trapno becomming ordinary fault subfield.
> - struct signalfd_siginfo is almost full
>
> This set of changes starts out with Marco's static_assert changes and
> additional one of my own that enforces the fact that the alignment of
> siginfo_t is also part of the ABI.  Together these build time
> checks verify there are no unexpected ABI changes in the changes
> that follow.
>
> The field si_trapno is changed to become an ordinary extension of the
> _sigfault member of siginfo.
>
> The code is refactored a bit and then si_perf_type is added along side
> si_perf_data in the _perf subfield of _sigfault of siginfo_t.
>
> Finally the signalfd_siginfo fields are removed as they appear to be
> filling up the structure without userspace actually being able to use
> them.

Thanks for your series, which is now in next-20210506.

>  arch/alpha/include/uapi/asm/siginfo.h              |   2 -
>  arch/alpha/kernel/osf_sys.c                        |   2 +-
>  arch/alpha/kernel/signal.c                         |   4 +-
>  arch/alpha/kernel/traps.c                          |  24 ++---
>  arch/alpha/mm/fault.c                              |   4 +-
>  arch/arm/kernel/signal.c                           |  39 +++++++
>  arch/arm64/kernel/signal.c                         |  39 +++++++
>  arch/arm64/kernel/signal32.c                       |  39 +++++++
>  arch/mips/include/uapi/asm/siginfo.h               |   2 -
>  arch/sparc/include/uapi/asm/siginfo.h              |   3 -
>  arch/sparc/kernel/process_64.c                     |   2 +-
>  arch/sparc/kernel/signal32.c                       |  37 +++++++
>  arch/sparc/kernel/signal_64.c                      |  36 +++++++
>  arch/sparc/kernel/sys_sparc_32.c                   |   2 +-
>  arch/sparc/kernel/sys_sparc_64.c                   |   2 +-
>  arch/sparc/kernel/traps_32.c                       |  22 ++--
>  arch/sparc/kernel/traps_64.c                       |  44 ++++----
>  arch/sparc/kernel/unaligned_32.c                   |   2 +-
>  arch/sparc/mm/fault_32.c                           |   2 +-
>  arch/sparc/mm/fault_64.c                           |   2 +-
>  arch/x86/kernel/signal_compat.c                    |  15 ++-

No changes needed for other architectures?
All m68k configs are broken with

arch/m68k/kernel/signal.c:626:35: error: 'siginfo_t' {aka 'struct
siginfo'} has no member named 'si_perf'; did you mean 'si_errno'?

See e.g. http://kisskb.ellerman.id.au/kisskb/buildresult/14537820/

There are still a few more references left to si_perf:

$ git grep -n -w si_perf
Next/merge.log:2902:Merging userns/for-next (4cf4e48fff05 signal: sort
out si_trapno and si_perf)
arch/m68k/kernel/signal.c:626:  BUILD_BUG_ON(offsetof(siginfo_t,
si_perf) != 0x10);
include/uapi/linux/perf_event.h:467:     * siginfo_t::si_perf, e.g. to
permit user to identify the event.
tools/testing/selftests/perf_events/sigtrap_threads.c:46:/* Unique
value to check si_perf is correctly set from
perf_event_attr::sig_data. */

Thanks!

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