linux-kernel - Re: [PATCH v2] md/bcache: Mark _

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Message-Id: <02B98CCF-15A9-46EE-AD00-C5EDCAE774F0@coly.li>
Date: Thu, 8 May 2025 23:59:43 +0800
From: Coly Li <i@...y.li>
To: Kees Cook <kees@...nel.org>
Cc: Coly Li <colyli@...nel.org>,
 Kent Overstreet <kent.overstreet@...ux.dev>,
 Ard Biesheuvel <ardb@...nel.org>,
 linux-bcache@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] md/bcache: Mark __nonstring look-up table



> 2025年5月8日 23:58，Kees Cook <kees@...nel.org> 写道：
> 
> On Thu, May 08, 2025 at 11:01:34AM +0800, Coly Li wrote:
>> 
>>> 2025年4月19日 11:55，Coly Li <i@...y.li> 写道：
>>> 
>>> 
>>> 
>>>> 2025年4月19日 04:21，Kees Cook <kees@...nel.org> 写道：
>>>> 
>>>> GCC 15's new -Wunterminated-string-initialization notices that the 16
>>>> character lookup table "zero_uuid" (which is not used as a C-String)
>>>> needs to be marked as "nonstring":
>>>> 
>>>> drivers/md/bcache/super.c: In function 'uuid_find_empty':
>>>> drivers/md/bcache/super.c:549:43: warning: initializer-string for array of 'char' truncates NUL terminator but destination lacks 'nonstring' attribute (17 chars into 16 available) [-Wunterminated-string-initialization]
>>>> 549 |         static const char zero_uuid[16] = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
>>>>    |                                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>> 
>>>> Add the annotation (since it is not used as a C-String), and switch the
>>>> initializer to an array of bytes.
>>>> 
>>>> Signed-off-by: Kees Cook <kees@...nel.org>
>>>> ---
>>>> v2: use byte array initializer (colyli)
>>>> v1: https://lore.kernel.org/all/20250416220135.work.394-kees@kernel.org/
>>>> Cc: Coly Li <colyli@...nel.org>
>>>> Cc: Kent Overstreet <kent.overstreet@...ux.dev>
>>>> Cc: Ard Biesheuvel <ardb@...nel.org>
>>>> Cc: linux-bcache@...r.kernel.org
>>>> ---
>>>> drivers/md/bcache/super.c | 3 ++-
>>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>> 
>>>> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
>>>> index e42f1400cea9..a76ce92502ed 100644
>>>> --- a/drivers/md/bcache/super.c
>>>> +++ b/drivers/md/bcache/super.c
>>>> @@ -546,7 +546,8 @@ static struct uuid_entry *uuid_find(struct cache_set *c, const char *uuid)
>>>> 
>>>> static struct uuid_entry *uuid_find_empty(struct cache_set *c)
>>>> {
>>>> - static const char zero_uuid[16] = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
>>>> + static const char zero_uuid[] __nonstring =
>>> 
>> 
>> Hi Kees,
>> 
>>> I notice zero_uuid[16] changes to zero_uuid[], then the element number information is removed.
>>> 
>>> Is it OK for GCC 15 to only add __nonstring and keep zero_uuid[16]?
> 
> Either way is fine. I can update the patch to use the "[16]" again if
> you'd like?
> 

Yes please. Thanks in advance.

Coly Li


> 
>> Ping ?
>> 
>> You are expert here, I need your opinion.
>> 
>> Thanks.
>> 
>> Coly Li
>> 
>> 
>> 
>>>> + { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
>>>> 
>>>> return uuid_find(c, zero_uuid);
>>>> }
>>>> -- 
>>>> 2.34.1
>> 
>> 
> 
> -- 
> Kees Cook