linux-kernel - Re: [PATCH v4 0/5] siginfo: ABI fixes for TRAP

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Message-ID: <CANpmjNOcZkC3YDSK8rA7yagRNBLCxyNRcUSKNbx69sR9PSW-2w@mail.gmail.com>
Date:   Tue, 18 May 2021 08:44:03 +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 v4 0/5] siginfo: ABI fixes for TRAP_PERF

On Tue, 18 May 2021 at 05:47, Eric W. Biederman <ebiederm@...ssion.com> wrote:
>
> Marco Elver <elver@...gle.com> writes:
>
> > On Mon, 17 May 2021 at 21:58, Eric W. Biederman <ebiederm@...ssion.com> wrote:
> >>
> >> During the merge window an issue with si_perf and the siginfo ABI came
> >> up.  The alpha and sparc siginfo structure layout had changed with the
> >> addition of SIGTRAP TRAP_PERF and the new field si_perf.
> >>
> >> The reason only alpha and sparc were affected is that they are the
> >> only architectures that use si_trapno.
> >>
> >> Looking deeper it was discovered that si_trapno is used for only
> >> a few select signals on alpha and sparc, and that none of the
> >> other _sigfault fields past si_addr are used at all.  Which means
> >> technically no regression on alpha and sparc.
> >>
> >> While the alignment concerns might be dismissed the abuse of
> >> si_errno by SIGTRAP TRAP_PERF does have the potential to cause
> >> regressions in existing userspace.
> >>
> >> While we still have time before userspace starts using and depending on
> >> the new definition siginfo for SIGTRAP TRAP_PERF this set of changes
> >> cleans up siginfo_t.
> >>
> >> - The si_trapno field is demoted from magic alpha and sparc status and
> >>   made an ordinary union member of the _sigfault member of siginfo_t.
> >>   Without moving it of course.
> >>
> >> - si_perf is replaced with si_perf_data and si_perf_type ending the
> >>   abuse of si_errno.
> >>
> >> - Unnecessary additions to signalfd_siginfo are removed.
> >>
> >> v3: https://lkml.kernel.org/r/m1tuni8ano.fsf_-_@fess.ebiederm.org
> >> v2: https://lkml.kernel.org/r/m14kfjh8et.fsf_-_@fess.ebiederm.org
> >> v1: https://lkml.kernel.org/r/m1zgxfs7zq.fsf_-_@fess.ebiederm.org
> >>
> >> This version drops the tests and fine grained handling of si_trapno
> >> on alpha and sparc (replaced assuming si_trapno is valid for
> >> all but the faults that defined different data).
> >
> > And just to clarify, the rest of the series (including static-asserts)
> > for the next merge-window will be sent once this series is all sorted,
> > correct?
>
> That is the plan.
>
> I really wonder about alphas use of si_trapno, and alphas use send_sig
> instead of force_sig.  It could be worth looking into those as it
> has the potential to simplify the code.
>
> >> Eric W. Biederman (5):
> >>       siginfo: Move si_trapno inside the union inside _si_fault
> >>       signal: Implement SIL_FAULT_TRAPNO
> >>       signal: Factor force_sig_perf out of perf_sigtrap
> >>       signal: Deliver all of the siginfo perf data in _perf
> >>       signalfd: Remove SIL_PERF_EVENT fields from signalfd_siginfo
> >
> > Looks good, thank you! I build-tested (defconfig -- x86_64, i386, arm,
> > arm64, m68k, sparc, alpha) this series together with a local patch to
> > pull in the static asserts from v3. Also re-ran perf_events kselftests
> > on x86_64 (native and 32bit compat).
>
> Thanks,
>
> Can I have your Tested-by?

Of course,

  Tested-by: Marco Elver <elver@...gle.com>

Thanks,
-- Marco