Re: [PATCH] ARCv2: Add explcit unaligned access support (and ability to disable too)

From: Guenter Roeck
Date: Thu Feb 28 2019 - 12:47:47 EST

On Wed, Jan 30, 2019 at 07:32:41PM +0300, Eugeniy Paltsev wrote:
> As of today we enable unaligned access unconditionally on ARCv2.
> Do this under a Kconfig option to allow disable it for test, benchmarking
> etc. Also while at it
> - Although gcc defaults to unaligned access (since GNU 2018.03), add the
> right toggles for enabling or disabling as appropriate
> - update bootlog to prints both HW feature status (exists, enabled/disabled)
> and SW status (used / not used).
> - wire up the relaxed memcpy for unaligned access
> Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@xxxxxxxxxxxx>
> Signed-off-by: Vineet Gupta <vgupta@xxxxxxxxxxxx>
> [vgupta: squashed patches, handle gcc -mno-unaligned-access quick]


with my brand-new gcc-8.3.0, built from upstream gcc, this patch
results in

arch/arc/kernel/setup.c: In function 'arc_cpu_mumbojumbo.constprop':
include/linux/compiler.h:348:38: error:
call to '__compiletime_assert_326' declared with attribute error: gcc doesn't support -mno-unaligned-access

when trying to build allnoconfig or tinyconfig. I get the same results
with gcc-8.2.0.

Do I need some special compiler configuration flag when building the
arcv2 toolchain ? Or am I simply out of luck for using upstream gcc ?