ARM64: Disabling warnings about deprecated armv8 instructions

[mzoran@crowfest.net (Michael Zoran)]

On Sun, 2017-01-22 at 09:43 +0000, Ard Biesheuvel wrote:
> On 22 January 2017 at 09:38, Michael Zoran <mzoran@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?

I'm saying that when running a ELF32 executable, the system needs to
fake the CPU architecture according to the uname system API and
/proc/cpuinfo.

Today, I run uname -a in Raspbian and I get aarch64.  I want it to
display arm6l or whatever to get Mathematica to load.

I see some code to make this work on other architectures such as X86,
but most of this appears to be unimplemented on arm64.