Re: [PATCH v4 0/5] siginfo: ABI fixes for TRAP_PERF

From: Marco Elver
Date: Mon May 17 2021 - 16:53:38 EST

On Mon, 17 May 2021 at 21:58, Eric W. Biederman <ebiederm@xxxxxxxxxxxx> 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:
> v2:
> v1:
> 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,

> 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).

-- Marco