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

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Message-ID: <VI1PR07MB486420A106A8BC85BEE9FB2AE4960@VI1PR07MB4864.eurprd07.prod.outlook.com>
Date:   Mon, 28 Jan 2019 13:28:40 +0000
From:   Bernd Edlinger <bernd.edlinger@...mail.de>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Arnd Bergmann <arnd@...db.de>
CC:     Laura Abbott <labbott@...hat.com>,
        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 1/25/19 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.