FCP-100: armv7 plan

[Jan Beich]

Warner Losh <imp at bsdimp.com> writes:

> On Sat, Sep 9, 2017 at 1:05 PM, Jan Beich <jbeich at vfemail.net> wrote:
>
>> Warner Losh <imp at bsdimp.com> writes:
>>
>> > Greetings,
>> >
>> > This will serve as 'Last Call' for any objections to the plan to create
>> an
>> > armv7 MACHINE_ARCH in FreeBSD, as documented in FCP-0100.
>> [...]
>>
>> Some ports want NEON support but FCP-0100 is vague about FreeBSD-specific
>> differences between armv6 and armv7. Clang appears to enable NEON for all
>> *-gnueabi* targets but I have no clue about GCC. Apparently, Android and
>> Debian don't assume NEON on armv7.
>>
>> related: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=221898
>>
>
> Yes. We are vague about it on purpose. Just like we're vague about MMX,
> MMX2, etc on x86 because different processors can/want use different
> things.

Do you mean similar to how FreeBSD i386 is vague about not supporting
real i386, only i486 or later?

> The goal, if it doesn't work already, is for NEON to work if used,
> but not be required, just like all the other optional features of a CPU.

FreeBSD doesn't support detecting NEON at runtime unlike Linux. Do you
mean at compile time? If so then the following probably needs to change

$ cc -target armv7-unknown-freebsd12.0-gnueabihf -dM -E -</dev/null |& fgrep -i neon
#define __ARM_NEON 1
#define __ARM_NEON_FP 0x4
#define __ARM_NEON__ 1