ARM64: Treat alignment faults as bus errors

[jhibbits]

Summary

ARM64 currently treats all data abort exceptions as page faults. This
can cause infinite loops on non-page fault faults, such as alignment faults.

Since kernel-side alignment faults should be avoided, this adds support directly
to the el0 fault handler, instead of the data_abort() handler.

Test Plan

Tested on rpi3, with a misaligned ldm test.

[andrew]

I've been thinking we should use a table of function pointers similar to how 32 bit arm does it. There are a few other cases that shouldn't be handled by data_abort.

sys/arm64/arm64/trap.c

418 ↗

(On Diff #63602)

I thing you want ISS_DATA_DFSC_MASK here.

[jhibbits]

sys/arm64/arm64/trap.c

418 ↗

(On Diff #63602)

You're right, that makes more sense.

[jhibbits]

Address @andrew's feedback. Use the right sub-mask to get the DFSC bits.

[andrew]

Can you rebase on top of D22170?

[jhibbits]

Rebase on top of D22170