Re: [2/2 ABI and toolchain part] Support Raspberry Pi [0-3] in big-endian mode

[Rin Okuyama <rokuyama.rk%gmail.com@localhost>]

On 2020/11/16 6:28, matthew green wrote:
> nice work.  i agree with your proposed changes in general.

Thank you!

> > Therefore,
> > (1) configure GCC not to emit unaligned access for earmv6{,hf}eb.
> >
> > http://www.netbsd.org/~rin/rpi_eb_gcc_20201115.patch
>
> this part doesn't seem right:
>
> -                         && arm_arch6 && (arm_arch_notm || arm_arch7));
> +          && arm_arch6 && ((arm_arch_notm && !BYTES_BIG_ENDIAN) || arm_arch7));
>
> i would have expected "&& !BYTES_BIG_ENDIAN" to have been
> added to the "arm_arch6", not the "arm_arch_notm" section.

This is not wrong;

	arm_arch6 && ((arm_arch_notm && !BYTES_BIG_ENDIAN) || arm_arch7)

is equivalent to

	(arm_arch6 && arm_arch_notm && !BYTE_BIG_ENDIAN) || arm_arch7

This is confusing, but I prioritized the original form.

> since this is really a hardware issue, and this is a bug
> all GCC arm, not netbsd target, it would be nice if you
> attempted merging this upstream as well :)

Unaligned access is possible for ARMv6 in BE8 big-endian mode, which
seems to be used for OSes other than NetBSD. While it is not possible
in BE32 big-endian mode for us.

Hmm, I started thinking that the fix should be restricted to NetBSD
target. But I don't know how to deal with this...

FreeBSD uses SUBTARGET_OVERRIDE_INTERNAL_OPTIONS. But, at the moment
when SUBTARGET_OVERRIDE_INTERNAL_OPTIONS is called,
opts_set->x_unaligned_access is already modified by
arm_option_override_internal().

Any ideas? Define new macro, e.g.,
SUBTARGET_OVERRIDE_UNALIGNED_ACCESS_OPTIONS in netbsd-eabi.h?

Thanks,
rin