Re: [PATCH] selftests/powerpc: Only test lwm/stmw on big endian

Hi!

On Tue, Jan 19, 2021 at 03:18:00PM +1100, Michael Ellerman wrote:

Newer binutils (>= 2.36) refuse to assemble lmw/stmw when building in
little endian mode. That breaks compilation of our alignment handler
test:

  /tmp/cco4l14N.s: Assembler messages:
  /tmp/cco4l14N.s:1440: Error: `lmw' invalid when little-endian
  /tmp/cco4l14N.s:1814: Error: `stmw' invalid when little-endian
  make[2]: *** [../../lib.mk:139: /output/kselftest/powerpc/alignment/alignment_handler] Error 1

These tests do pass on little endian machines, as the kernel will
still emulate those instructions even when running little
endian (which is arguably a kernel bug).

The opposite: in older ISAs it is *required* to.  On all very old ISA
versions, and when not on the Server Environment on everything before
ISA 2.07.

Many older implementations did an alignment interrupt, but that was an
implementation detail (they could still be compliant with proper system
software support, e.g. kernel emulation handlers).  Nowadays that
interrupt is required, so you can still support it like that.

(The patch is fine of course.)


Segher