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

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Message-Id: <851B250D-A22C-4B47-BBAC-55284B5B5790@coly.li>
Date: Thu, 8 May 2025 11:01:34 +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]?

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