Summary:
POWER architecture CPUs (Book-S) require natural alignment for
cache-inhibited storage accesses. Since we can't know the caching model
for a page ahead of time, always enforce natural alignment in memcpy.
This fixes a SIGBUS in X with acceleration enabled on POWER9.
As part of this, revert r358672, it's no longer necessary with this fix.
Regression tested by alfredo.
Reviewed by: alfredo
Differential Revision: https://reviews.freebsd.org/D23969
For copies shorter than 512 bytes, the data is copied using plain
ld/std instructions.
For 512 bytes or more, the copy is done in 3 phases:
Phase 1: copy from the src buffer until it's aligned at a 16-byte boundary
Phase 2: copy as many aligned 64-byte blocks from the src buffer as possible
Phase 3: copy the remaining data, if any
In phase 2, this code uses VSX instructions when available. Otherwise,
it uses ldx/stdx.
Submitted by: Luis Pires <lffpires_ruabrasil.org> (original version)
Reviewed by: jhibbits
Differential Revision: https://reviews.freebsd.org/D15118
