linux-kernel - Re: [PATCH v2 2/2] auxdisplay: panel: avoid gcc 8's Wstringop-truncation warning

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Message-ID: <CANiq72=sKO_QxujKSY7ZJSaVfT0-4atk+4U8fJFsmLJLxrjhzQ@mail.gmail.com>
Date:   Wed, 1 Aug 2018 21:50:09 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>, Willy Tarreau <w@....eu>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Martin Sebor <msebor@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v2 2/2] auxdisplay: panel: avoid gcc 8's
 Wstringop-truncation warning

On Wed, Aug 1, 2018 at 8:47 PM, Kees Cook <keescook@...omium.org> wrote:
> On Wed, Aug 1, 2018 at 10:58 AM, Miguel Ojeda
> <miguel.ojeda.sandonis@...il.com> wrote:
>> Let gcc know it is not meant to be NUL-terminated by annotating with
>> the new __nonstring variable attribute; and remove the comment since it
>> conveys the same information.
>>
>> Cc: Willy Tarreau <w@....eu>
>> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
>> Cc: Martin Sebor <msebor@...il.com>
>> Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
>> ---
>>  drivers/auxdisplay/panel.c | 7 +++----
>>  1 file changed, 3 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/auxdisplay/panel.c b/drivers/auxdisplay/panel.c
>> index 3b25a643058c..21b9b2f2470a 100644
>> --- a/drivers/auxdisplay/panel.c
>> +++ b/drivers/auxdisplay/panel.c
>> @@ -155,10 +155,9 @@ struct logical_input {
>>                         int release_data;
>>                 } std;
>>                 struct {        /* valid when type == INPUT_TYPE_KBD */
>> -                       /* strings can be non null-terminated */
>> -                       char press_str[sizeof(void *) + sizeof(int)];
>> -                       char repeat_str[sizeof(void *) + sizeof(int)];
>> -                       char release_str[sizeof(void *) + sizeof(int)];
>> +                       char press_str[sizeof(void *) + sizeof(int)] __nonstring;
>> +                       char repeat_str[sizeof(void *) + sizeof(int)] __nonstring;
>> +                       char release_str[sizeof(void *) + sizeof(int)] __nonstring;
>>                 } kbd;
>>         } u;
>>  };
>
> If it's not a string, why not use "u8" instead of "char"? Does the
> warning persist?

Yes, it persists (on purpose). Originally it didn't, but see the discussion at:

  https://www.spinics.net/lists/kernel/msg2737596.html

And:

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84725

Cheers,
Miguel

>
> -Kees
>
> --
> Kees Cook
> Pixel Security