Marco Elver [off-list ref] writes:

On Sat, 1 May 2021 at 00:50, Eric W. Biederman [off-list ref] wrote:

quoted

It turns out that linux uses si_trapno very sparingly, and as such it
can be considered extra information for a very narrow selection of
signals, rather than information that is present with every fault
reported in siginfo.

As such move si_trapno inside the union inside of _si_fault.  This
results in no change in placement, and makes it eaiser to extend
_si_fault in the future as this reduces the number of special cases.
In particular with si_trapno included in the union it is no longer a
concern that the union must be pointer alligned on most architectures
because the union followes immediately after si_addr which is a
pointer.

Maybe add "Link:
https://lkml.kernel.org/r/CAK8P3a0+uKYwL1NhY6Hvtieghba2hKYGD6hcKx5n8=4Gtt+pHA@mail.gmail.com"

quoted

Signed-off-by: "Eric W. Biederman" <redacted>

Acked-by: Marco Elver <elver@google.com>

By no longer guarding it with __ARCH_SI_TRAPNO we run the risk that it
will be used by something else at some point. Is that intentional?

The motivation was letting the code be tested on other architectures.

But once si_trapno falls inside the union instead of being present for
every signal reporting a fault it doesn't really matter.

I think it would be poor taste but harmless to use si_trapno, mostly
because defining a new entry in the union could be more specific and
well defined.

Eric