linux-kernel - Re: [RFC][PATCH] Update -Wattribute-alias for gcc9

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Date:   Mon, 28 Jan 2019 15:35:24 +0100
From:   Laura Abbott <labbott@...hat.com>
To:     Bernd Edlinger <bernd.edlinger@...mail.de>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Arnd Bergmann <arnd@...db.de>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Martin Sebor <msebor@...il.com>
Subject: Re: [RFC][PATCH] Update -Wattribute-alias for gcc9

On 1/28/19 5:28 AM, Bernd Edlinger wrote:
> On 1/25/19 1:24 PM, Bernd Edlinger wrote:
>> On 1/25/19 12:39 PM, Miguel Ojeda wrote:
>>> On Fri, Jan 25, 2019 at 11:58 AM Arnd Bergmann <arnd@...db.de> wrote:
>>>>
>>>> On Fri, Jan 25, 2019 at 11:43 AM Laura Abbott <labbott@...hat.com> wrote:
>>>>>
>>>>> Commit bee20031772a ("disable -Wattribute-alias warning for
>>>>> SYSCALL_DEFINEx()") disabled -Wattribute-alias with gcc8.
>>>>> gcc9 changed the format of -Wattribute-alias to take a parameter.
>>>>> This doesn't quite match with the existing disabling mechanism
>>>>> so update for gcc9 to match with the default (-Wattribute-alias=1).
>>>>>
>>>>> Signed-off-by: Laura Abbott <labbott@...hat.com>
>>>>> ---
>>>>> This is RFC because it feels ugly. I went ahead and did the obvious fixup
>>>>> but it's worth discussing if we're going to end up with an explosion or
>>>>> if there's a better way to handle this in one macro.
>>>>
>>>> Bernd Edlinger has sent a patch to gcc for this:
>>>> https://gcc.gnu.org/ml/gcc-patches/2019-01/msg01120.html
>>>>
>>>> and Miguel Ojeda said he wanted to send a patch for it to the
>>>> kernel as well, not sure if he wanted to take a different
>>>> approach there, so adding both to Cc here.
>>>
>>> Thanks Arnd (I was working with Martin on the expanded
>>> -Wmissing-attribute warnings, not on this, but thanks nevertheless :).
>>>
>>> Martin/Bernd: from the GCC mailing list I am not sure if we should
>>> expect the old behavior to be maintained or not.
>>>
>>
>> I believe it is not intentional to break the old syntax of the
>> pragma.  There will be new -Wattribute-alias=1 and -Wattribute-alias=2
>> and -Wattribute-alias is easy to retain as an alias for -Wattribute-alias=1.
>> That is what my patch will do.
>>
> 
> Okay, I committed the -Wattribute-alias patch to gcc trunk, now
> as https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=268336 .
> So there will be no need for a workaround on your side.
> 
> Also fixed a few false positive -Waddress-of-packed-member warnings with
> https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=268118 and
> https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=268337 .
> 
> However there remain a lot of warnings from -Waddress-of-packed-member,
> that look more or less valid, has anybody an idea how to handle
> these?
> 
> 
> Bernd.
> 

Thanks, I'll keep an eye out when this lands in Fedora gcc.
I think once everything lands it will be easier to work on
the remaining -Waddress-of-packed-member.

Laura