linux-kernel - RE: [PATCH] LoongArch: Make -mstrict-align be configurable

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Date:   Thu, 2 Feb 2023 09:01:34 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Huacai Chen' <chenhuacai@...ngson.cn>,
        Arnd Bergmann <arnd@...db.de>,
        Huacai Chen <chenhuacai@...nel.org>
CC:     "loongarch@...ts.linux.dev" <loongarch@...ts.linux.dev>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Guo Ren <guoren@...nel.org>, Xuerui Wang <kernel@...0n.name>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] LoongArch: Make -mstrict-align be configurable

From: Huacai Chen
> Sent: 02 February 2023 08:43
> 
> Introduce Kconfig option ARCH_STRICT_ALIGN to make -mstrict-align be
> configurable.
> 
> Not all LoongArch cores support h/w unaligned access, we can use the
> -mstrict-align build parameter to prevent unaligned accesses.
> 
> This option is disabled by default to optimise for performance, but you
> can enabled it manually if you want to run kernel on systems without h/w
> unaligned access support.

Should there be an associated run-time check during kernel initialisation
that a kernel compiled without -mstrict-align isn't being run on hardware
that doesn't support unaligned accesses.

It can be quite a while before you get a compiler-generated misaligned accesses.

Also isn't there a HAVE_EFFICIENT_MISALIGNED_ACCESS define that would
also need to be set correctly??

	David

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