[PATCH 0/2] MIPS: memset: Fix `noreorder' issues

From: Maciej W. Rozycki
Date: Tue Oct 02 2018 - 07:50:05 EST


Hi,

A recent change broke CPU_DADDI_WORKAROUNDS support in memset.S, due to a
delay-slot instruction expanding to multiple hardware operations for the
affected configurations.

The underlying cause is the excessive use of the `noreorder' assembly
mode, while it is only needed in couple of places where either there is a
data dependency between a branch and its delay slot instruction, or there
is a section switch involved that would prevent automatic delay slot
scheduling.

These changes address both problems and for clarity, not to mix multiple
conceptually separate changes and to make backporting easier I made them a
small patch series. See individual change descriptions for details.

This has been build-time and run-time verified with 32-bit and 64-bit
DECstation configurations, build-time verified with big-endian and
little-endian 64-bit SWARM configurations. Build-time verification was
made by running `objdump -d arch/mips/lib/memset.o' with a pristine and
and a patched build to make sure there has been no change in machine code
generation, except for the delay-slot multiple instruction with the 64-bit
CPU_DADDI_WORKAROUNDS DECstation configuration.

Please apply.

Maciej