From mboxrd@z Thu Jan  1 00:00:00 1970
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH 3/7] x86, LLVM: suppress clang warnings about unaligned
 accesses
Date: Thu, 13 Apr 2017 16:55:00 -0700
Message-ID: <3b743cf7-3d81-1fd6-b3a9-2f58a3bd8817@zytor.com>
References: <20170317001520.85223-1-md@google.com>
 <20170317001520.85223-4-md@google.com>
 <FB827022-C732-432A-8F31-734C88EBF7A4@zytor.com>
 <20170403230158.GA145051@google.com> <20170413231439.GG28657@google.com>
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Cc: Michael Davidson <md@google.com>, Michal Marek <mmarek@suse.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Shaohua Li <shli@kernel.org>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>, x86@kernel.org,
        linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-crypto@vger.kernel.org, linux-raid@vger.kernel.org
To: Matthias Kaehlcke <mka@chromium.org>
Return-path: <linux-kbuild-owner@vger.kernel.org>
In-Reply-To: <20170413231439.GG28657@google.com>
Sender: linux-kbuild-owner@vger.kernel.org
List-Id: linux-crypto.vger.kernel.org

On 04/13/17 16:14, Matthias Kaehlcke wrote:
> El Mon, Apr 03, 2017 at 04:01:58PM -0700 Matthias Kaehlcke ha dit:
> 
>> El Fri, Mar 17, 2017 at 04:50:19PM -0700 hpa@zytor.com ha dit:
>>
>>> On March 16, 2017 5:15:16 PM PDT, Michael Davidson <md@google.com> wrote:
>>>> Suppress clang warnings about potential unaliged accesses
>>>> to members in packed structs. This gets rid of almost 10,000
>>>> warnings about accesses to the ring 0 stack pointer in the TSS.
>>>>
>>>> Signed-off-by: Michael Davidson <md@google.com>
>>>> ---
>>>> arch/x86/Makefile | 5 +++++
>>>> 1 file changed, 5 insertions(+)
>>>>
>>>> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
>>>> index 894a8d18bf97..7f21703c475d 100644
>>>> --- a/arch/x86/Makefile
>>>> +++ b/arch/x86/Makefile
>>>> @@ -128,6 +128,11 @@ endif
>>>>         KBUILD_CFLAGS += $(call cc-option,-maccumulate-outgoing-args)
>>>> endif
>>>>
>>>> +ifeq ($(cc-name),clang)
>>>> +# Suppress clang warnings about potential unaligned accesses.
>>>> +KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
>>>> +endif
>>>> +
>>>> ifdef CONFIG_X86_X32
>>>> 	x32_ld_ok := $(call try-run,\
>>>> 			/bin/echo -e '1: .quad 1b' | \
>>>
>>> Why conditional on clang?
>>
>> My understanding is that this warning is clang specific, it is not
>> listed on https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
> 
> Actually this warning affects other platforms besides x86
> (e.g. arm64), I'll submit a patch that disables the warning on all
> platforms.
> 

Drop the ifeq ($(cc-name),clang).

You should assume that if you have to add one of those ifeq's then you
are doing something fundamentally wrong.

	-hpa