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

On Tue, Jan 23, 2024 at 06:11:52PM +0000, Mark Brown wrote:

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

quoted

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.

[...]

I don't feel that strongly about it.

Ideally we'd have gone for the fully relaxed approach from the start,
but it's hard to test whether "unspecified" registers aren't leaking
data from somewhere they shouldn't.

Given that the decision has been made anyway, the documentation should
not send mixed messages, so:

Reviewed-by: Dave Martin <Dave.Martin@arm.com>


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel