Re: [PATCH 1/4] arm64/sve: Remove bitrotted comment about syscall behaviour

On Tue, Jan 23, 2024 at 05:54:17PM +0000, Dave Martin wrote:

I still feel that it is iffy practice for userspace to rely on the
extra bits being zeroed -- I think the architecture hides this
guarantee anyway whenever you go through a function call confirming to
the regular procedure call standard (including the syscall wrappers).
But there may not be a lot of point trying to put people off if we
can't force them not to rely on it.

I do tend to agree that the requirement to zero is excessively zealous
and that the risk from relaxing it is minor (it's stricter than the
function call ABI), I did leave a sysctl as a mechanism for restoring
compatibility in the case where we did run into issues in my original
series but I didn't expect to need it.  If you convince everyone else
I'd be happy to relax things but I don't super care either way.