ARM64: Disabling warnings about deprecated armv8 instructions

[Ard Biesheuvel]

On 22 January 2017 at 08:58, Michael Zoran <mzoran at crowfest.net> 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.
>
> I can double check, but I think the instructions are being emulated in
> hardware so they are just filling the log and slowing things down.
>
> [10685.558480] cp15barrier_handler: 197896 callbacks suppressed
> [10685.558487] "Xorg" (656) uses deprecated CP15 Barrier instruction at
> 0xf707fe9c
> [10685.558504] "Xorg" (656) uses deprecated CP15 Barrier instruction at
> 0xf7015944
> [10685.558511] "Xorg" (656) uses deprecated CP15 Barrier instruction at
> 0xf7012494
> [10685.558518] "Xorg" (656) uses deprecated CP15 Barrier instruction at
> 0xf70159b4
> [10685.558527] "Xorg" (656) uses deprecated CP15 Barrier instruction at
> 0xf7011478
> [10685.558533] "Xorg" (656) uses deprecated CP15 Barrier instruction at
> 0xf70114e8
> [10685.558540] "Xorg" (656) uses deprecated CP15 Barrier instruction at
> 0xf7015944
> [10685.558547] "Xorg" (656) uses deprecated CP15 Barrier instruction at
> 0xf7012494
> [10685.558553] "Xorg" (656) uses deprecated CP15 Barrier instruction at
> 0xf70159b4
> [10685.558560] "Xorg" (656) uses deprecated CP15 Barrier instruction at
> 0xf7011478
> [10685.559179] compat_setend_handler: 1078 callbacks suppressed
> [10685.559188] "systemd-journal" (138) uses deprecated setend
> instruction at 0xf76a66f4
> [10685.559196] "systemd-journal" (138) uses deprecated setend
> instruction at 0xf76a6bd8
> [10685.559209] "systemd-journal" (138) uses deprecated setend
> instruction at 0xf76a66f4
> [10685.559216] "systemd-journal" (138) uses deprecated setend
> instruction at 0xf76a6bd8
> [10685.559231] "systemd-journal" (138) uses deprecated setend
> instruction at 0xf76a66f4
> [10685.559237] "systemd-journal" (138) uses deprecated setend
> instruction at 0xf76a6bd8
> [10685.559246] "systemd-journal" (138) uses deprecated setend
> instruction at 0xf76a66f4
> [10685.559253] "systemd-journal" (138) uses deprecated setend
> instruction at 0xf76a6bd8
> [10685.559269] "systemd-journal" (138) uses deprecated setend
> instruction at 0xf76a66f4
> [10685.559276] "systemd-journal" (138) uses deprecated setend
> instruction at 0xf76a6bd8
>

You can disable the emulation by doing

echo 2 >/proc/sys/abi/setend
echo 2 >/proc/sys/abi/cp15_barrier