ARM64: Disabling warnings about deprecated armv8 instructions

[Måns Rullgård]

Michael Zoran <mzoran at crowfest.net> writes:

> On Mon, 2017-01-30 at 17:09 +0000, Ard Biesheuvel wrote:
>> Well, the question is really how to deal with 32-bit compatibility
>> given the fact that the ARM architecture will drop such instructions
>> in its next revision. Whether we agree with that, and whether we
>> should argue our positions with the architects if we don't is not
>> relevant here.
>> 
>> What is relevant is whether we inform userspace if we spot such a
>> deprecated instruction, and I think we should.
>> 
>> Note that this is not only an issue for the arm64 kernel. The 32-bit
>> kernel will have the exact same issue when you try to run it on
>> hardware that no longer has support for those instructions.
>
> Just to inject two cents worth since I'm still on the thread and I
> originally started the topic...
>
> The Intel comparison seems relevant.  I think in theory you can still
> run old MS-DOS software on an Intel PC if you were so inclined to do
> so.
>
> I would think the best would be to turn the warnings off by default
> when running in 32 bit mode with the option to turn them back on.  Then
> as time progresses more of more of these instructions can be converted
> to software emulation and removed from the hardware.  And hopefully as
> time progresses, all the user mode software gets upgraded to 64 bit so
> that 32 bit get dropped.
>
> The issue seems to me to be more that the kernel is screaming in the
> logs rather then if it's emulating the instructions in hardware or
> software.

Might warning once be an acceptable compromise?

-- 
Måns Rullgård