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From:   Vineet Gupta <vineet.gupta1@synopsys.com>
To:     Guenter Roeck <linux@roeck-us.net>,
        Eugeniy Paltsev <eugeniy.paltsev@synopsys.com>
CC:     Claudiu Zissulescu <claudiu.zissulescu@synopsys.com>,
        "linux-snps-arc@lists.infradead.org" 
        <linux-snps-arc@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ARCv2: Add explcit unaligned access support (and
 ability to disable too)
Thread-Topic: [PATCH] ARCv2: Add explcit unaligned access support (and
 ability to disable too)
Thread-Index: AQHUz422b40bhmdW702O6EC/CP0bNQ==
Date:   Thu, 28 Feb 2019 18:12:33 +0000
Message-ID: <C2D7FE5348E1B147BCA15975FBA2307501464380DE@US01WEMBX2.internal.synopsys.com>
References: <20190228174742.GA18868@roeck-us.net>
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On 2/28/19 9:47 AM, Guenter Roeck wrote:=0A=
> On Wed, Jan 30, 2019 at 07:32:41PM +0300, Eugeniy Paltsev wrote:=0A=
>> As of today we enable unaligned access unconditionally on ARCv2.=0A=
>> Do this under a Kconfig option to allow disable it for test, benchmarkin=
g=0A=
>> etc. Also while at it=0A=
>>=0A=
>>   - Select HAVE_EFFICIENT_UNALIGNED_ACCESS=0A=
>>   - Although gcc defaults to unaligned access (since GNU 2018.03), add t=
he=0A=
>>     right toggles for enabling or disabling as appropriate=0A=
>>   - update bootlog to prints both HW feature status (exists, enabled/dis=
abled)=0A=
>>     and SW status (used / not used).=0A=
>>   - wire up the relaxed memcpy for unaligned access=0A=
>>=0A=
>> Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>=0A=
>> Signed-off-by: Vineet Gupta <vgupta@synopsys.com>=0A=
>> [vgupta: squashed patches, handle gcc -mno-unaligned-access quick]=0A=
> Hi,=0A=
>=0A=
> with my brand-new gcc-8.3.0, built from upstream gcc, this patch=0A=
> results in=0A=
>=0A=
> arch/arc/kernel/setup.c: In function 'arc_cpu_mumbojumbo.constprop':=0A=
> include/linux/compiler.h:348:38: error:=0A=
> 	call to '__compiletime_assert_326' declared with attribute error: gcc do=
esn't support -mno-unaligned-access=0A=
=0A=
Sorry it broke ur build - but it did catch a deficiency in compiler as inte=
nded -=0A=
yay !=0A=
=0A=
> when trying to build allnoconfig or tinyconfig. I get the same results=0A=
> with gcc-8.2.0.=0A=
=0A=
Unaligned access code gen was enabled by default in 7.x actually, but us OS=
 folks=0A=
were late to find that which led to the recent patch to disable it which wa=
s=0A=
broken in gcc.=0A=
Claudiu fixed gcc promptly but that patch didn't make it to upstream, which=
 I've=0A=
posted now.=0A=
=0A=
http://lists.infradead.org/pipermail/linux-snps-arc/2019-February/005522.ht=
ml=0A=
=0A=
> Do I need some special compiler configuration flag when building the=0A=
> arcv2 toolchain ? Or am I simply out of luck for using upstream gcc ?=0A=
=0A=
Once the patch hits mainline you could use that. In the mean time I'll back=
 out=0A=
the "detector" as it might trip other people too.=0A=
=0A=
Many Thx for your testing service.=0A=
-Vineet=0A=