linux-kernel - Re: [PATCH] kbuild: fix kernel/bounds.c 'W=1' warning

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Date:   Mon, 8 Oct 2018 11:00:10 +0100
From:   Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        miguel.ojeda.sandonis@...il.com
Cc:     Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH] kbuild: fix kernel/bounds.c 'W=1' warning

On 06/10/18 23:06, Masahiro Yamada wrote:
> On Sun, Oct 7, 2018 at 6:58 AM Masahiro Yamada
> <yamada.masahiro@...ionext.com> wrote:
>>
>> Hi Miguel,
>>
>>
>> On Sun, Oct 7, 2018 at 6:18 AM Miguel Ojeda
>> <miguel.ojeda.sandonis@...il.com> wrote:
>>>
>>> On Fri, Oct 5, 2018 at 10:35 AM Arnd Bergmann <arnd@...db.de> wrote:
>>>>
>>>> Building any configuration with 'make W=1' produces a warning:
>>>>
>>>> kernel/bounds.c:16:6: warnign: no previous prototype for 'foo' [-Wmissing-prototypes]
>>>>
>>>> When also passing -Werror, this prevents us from building any
>>>> other files. Nobody ever calls the function, but we can't make
>>>> it 'static' either since we want the compiler output.
>>>>
>>>> Calling it 'main' instead however avoids the warning, because gcc
>>>> does not insist on having a declaration for main.
>>>
>>> I think marking the function as static __used should do the trick and
>>> would be less confusing.
>>
>>
>>
>>
>> I tried __used, but I still see the warning.
>>
>>
>> masahiro@...ver:~/ref/linux$ git diff
>> diff --git a/kernel/bounds.c b/kernel/bounds.c
>> index c373e88..aee0101 100644
>> --- a/kernel/bounds.c
>> +++ b/kernel/bounds.c
>> @@ -13,7 +13,7 @@
>>  #include <linux/log2.h>
>>  #include <linux/spinlock_types.h>
>>
>> -void foo(void)
>> +void __used foo(void)
>>  {
>>         /* The enum constants to put into include/generated/bounds.h */
>>         DEFINE(NR_PAGEFLAGS, __NR_PAGEFLAGS);
>> masahiro@...ver:~/ref/linux$ make W=1  prepare
>>   CC      kernel/bounds.s
>> kernel/bounds.c:16:13: warning: no previous prototype for ‘foo’
>> [-Wmissing-prototypes]
>>  void __used foo(void)
>>              ^
>>   CC      arch/x86/kernel/asm-offsets.s
> 
> 
> 
> Sorry, I forgot to add 'static'.
> 
> Adding both static and __used worked for me,
> and I like the idea.
> 

Aha - I'd also tried converting to static in my earlier attempts, but
didn't realise we had __used!

updating as "static __used" causes the following diff:

diff -Nurp bounds.s.foo bounds.s.static-used
--- bounds.s.foo        2018-10-05 10:20:53.269941404 +0100
+++ bounds.s.static-used        2018-10-08 10:51:18.079309049 +0100
@@ -110,7 +110,6 @@
 #NO_APP
        .align  2
        .p2align 3,,7
-       .global foo
        .type   foo, %function
 foo:
        stp     x29, x30, [sp, -16]!    //,,,


I'd say this is a pretty good alternative fix - however I see Arnd's
version is already on it's way though akpm's tree...

https://ozlabs.org/~akpm/mmots/broken-out/kbuild-fix-kernel-boundsc-w%3D1-warning.patch

Anyway, as long as one of the variants gets there I'll be happy :)

--
Regards

Kieran