ARM64: Disabling warnings about deprecated armv8 instructions

[Ard Biesheuvel]

On 22 January 2017 at 09:38, Michael Zoran <mzoran at crowfest.net> wrote:
> On Sun, 2017-01-22 at 17:05 +0800, Jisheng Zhang wrote:
>> On Sun, 22 Jan 2017 00:58:48 -0800 Michael Zoran wrote:
>>
>> > On Sun, 2017-01-22 at 09:52 +0100, Alexander Stein wrote:
>> > > Hi Michael,
>> > >
>> > > On Sunday, January 22, 2017, 12:07:04 AM CET Michael Zoran
>> > > wrote:
>> > > > I'm not sure if this if the correct place to be asking
>> > > > this.   The
>> > > > RPI
>> > > > 3 running ARM64 is slowly reaching the point of being about to
>> > > > seriously run a 32 bit vender OS like Raspbian.  When running
>> > > > Raspbian,
>> > > > I'm seeing a very large number(thousands) of kernel log
>> > > > messages
>> > > > about
>> > > > deprecated instructions especially setend and barrier
>> > > > instuctions.
>> > > > This can be very annoying and is completely filling the kernel
>> > > > log.
>> > > >
>> > > > I'm considering submitting a patch to add a Kconfig option to
>> > > > disable
>> > > > these warnings with the default being to keep the warnings
>> > > > enabled.  I
>> > > > was wondering if such a patch could be seriously considered.
>> > >
>> > > Could you please provide an example of those warning an what is
>> > > trigging
>> > > those?
>> > >
>> > > Thanks and best regards,
>> > > Alexander
>> >
>> > Sure, here is a snipped from dmesg.  I think this is happening
>> > because
>> > the entire Raspbian OS is compiled with a custom gcc compiler that
>> > is
>> > targeting arm6+VFP.
>>
>> IMHO, this is the root cause. I didn't see below warnings from dmesg
>> with
>> armhf debian and ubuntu If the underlying HW is armv8 compatible, it
>> doesn't make sense to target the compiler to armv6
>>
>>
>
> Advanced users can install a different OS. Beginners can't and will
> need a single OS image for simple install.
>

That single OS image can simply test for the presence of
/proc/sys/abi, and perform the writes if it is there.

> Does anybody know if these instructions are detected at runtime?

What do you mean by 'detected'?

> I'm
> also looking into an issue with Mathmatica due to broken OS detection.
> It appears that arm64 is currently missing some of the CPU spoofing
> that happens on other architectures...
>

Could you elaborate? What do you think should be there that isn't?