Re: siginfo_t ABI break on sparc64 from si_addr_lsb move 3y ago

On Fri, Apr 30, 2021 at 7:08 PM Eric W. Biederman [off-list ref] wrote:

The code is only safe if the analysis that says we can move si_trapno
and perhaps the ia64 fields into the union is correct.  It looks like
ia64 much more actively uses it's signal extension fields including for
SIGTRAP, so I am not at all certain the generic definition of
perf_sigtrap is safe on ia64.

quoted

I suppose in theory sparc64 or alpha might start using the other
fields in the future, and an application might be compiled against
mismatched headers, but that is unlikely and is already broken
with the current headers.

If we localize the use of si_trapno to just a few special cases on alpha
and sparc I think we don't even need to worry about breaking userspace
on any architecture.  It will complicate siginfo_layout, but it is a
complication that reflects reality.

Ok.

I don't have a clue how any of this affects ia64.  Does perf work on
ia64?  Does perf work on sparc, and alpha?

If perf works on ia64 we need to take a hard look at what is going on
there as well.

ia64 never had perf support. It had oprofile until very recently, and it
had a custom thing before that. My feeling is that it's increasingly
unlikely to ever gain perf support in the future, given that oprofile
(in user space) has required kernel perf support (in kernel) for a
long time and nobody cared about that being broken either.

sparc64 has perf support for Sun UltraSPARC 3/3+/3i/4+/T1/T2/T3
and Oracle SPARC T4/T5/M7 but lacks support for most CPUs from
Oracle, Fujitsu and the rest, in particular anything from the last
ten years.
Alpha has perf support for EV67, EV68, EV7, EV79, and EV69, i.e.
anything from 1996 to the end in 2004.

      Arnd