[PATCH] md/bcache: Mark __nonstring look-up table

[PATCH] md/bcache: Mark __nonstring look-up table

[Kees Cook]

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 to silence the GCC warning.

Signed-off-by: Kees Cook <kees@kernel.org>
---
Cc: Coly Li <colyli@kernel.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: linux-bcache@vger.kernel.org
---
 drivers/md/bcache/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index e42f1400cea9..577d048170fe 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -546,7 +546,7 @@ 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 = "\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

Re: [PATCH] md/bcache: Mark __nonstring look-up table

[Coly Li]

> 2025年4月17日 06:01，Kees Cook <kees@kernel.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 to silence the GCC warning.
> 
> Signed-off-by: Kees Cook <kees@kernel.org>
> ---
> Cc: Coly Li <colyli@kernel.org>
> Cc: Kent Overstreet <kent.overstreet@linux.dev>
> Cc: linux-bcache@vger.kernel.org <mailto:linux-bcache@vger.kernel.org>   

It looks good to me. Thanks for the fix up.


Coly Li



> ---
> drivers/md/bcache/super.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index e42f1400cea9..577d048170fe 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -546,7 +546,7 @@ 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 = "\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
> 
> 

Re: [PATCH] md/bcache: Mark __nonstring look-up table

[Ard Biesheuvel]

On Thu, 17 Apr 2025 at 00:01, Kees Cook <kees@kernel.org> wrote:
>
> 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 to silence the GCC warning.
>
> Signed-off-by: Kees Cook <kees@kernel.org>
> ---
> Cc: Coly Li <colyli@kernel.org>
> Cc: Kent Overstreet <kent.overstreet@linux.dev>
> Cc: linux-bcache@vger.kernel.org
> ---
>  drivers/md/bcache/super.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index e42f1400cea9..577d048170fe 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -546,7 +546,7 @@ 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 = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
>

Just

static const char zero_uuid[16] = {};

should work fine here too. No need for the initializer.


>         return uuid_find(c, zero_uuid);
>  }
> --
> 2.34.1
>
>

Re: [PATCH] md/bcache: Mark __nonstring look-up table

[Kees Cook]

On April 16, 2025 11:16:45 PM PDT, Ard Biesheuvel <ardb@kernel.org> wrote:
>On Thu, 17 Apr 2025 at 00:01, Kees Cook <kees@kernel.org> wrote:
>>
>> 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 to silence the GCC warning.
>>
>> Signed-off-by: Kees Cook <kees@kernel.org>
>> ---
>> Cc: Coly Li <colyli@kernel.org>
>> Cc: Kent Overstreet <kent.overstreet@linux.dev>
>> Cc: linux-bcache@vger.kernel.org
>> ---
>>  drivers/md/bcache/super.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
>> index e42f1400cea9..577d048170fe 100644
>> --- a/drivers/md/bcache/super.c
>> +++ b/drivers/md/bcache/super.c
>> @@ -546,7 +546,7 @@ 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 = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
>>
>
>Just
>
>static const char zero_uuid[16] = {};
>
>should work fine here too. No need for the initializer.

🤦 Yes. This is what I get for fixing dozens of these. I'll send a v2...

-Kees


-- 
Kees Cook

Re: [PATCH] md/bcache: Mark __nonstring look-up table

[Coly Li]

> 2025年4月17日 15:10，Kees Cook <kees@kernel.org> 写道：
> 
> 
> 
> On April 16, 2025 11:16:45 PM PDT, Ard Biesheuvel <ardb@kernel.org> wrote:
>> On Thu, 17 Apr 2025 at 00:01, Kees Cook <kees@kernel.org> wrote:
>>> 
>>> 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 to silence the GCC warning.
>>> 
>>> Signed-off-by: Kees Cook <kees@kernel.org>
>>> ---
>>> Cc: Coly Li <colyli@kernel.org>
>>> Cc: Kent Overstreet <kent.overstreet@linux.dev>
>>> Cc: linux-bcache@vger.kernel.org
>>> ---
>>> drivers/md/bcache/super.c | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>> 
>>> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
>>> index e42f1400cea9..577d048170fe 100644
>>> --- a/drivers/md/bcache/super.c
>>> +++ b/drivers/md/bcache/super.c
>>> @@ -546,7 +546,7 @@ 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 = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
>>> 
>> 
>> Just
>> 
>> static const char zero_uuid[16] = {};
>> 
>> should work fine here too. No need for the initializer.
> 
> 🤦 Yes. This is what I get for fixing dozens of these. I'll send a v2...


Can we do this,

static const char zero_uuid[16] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};

I like the explicit array element number 16, and the explicit uuid content by obvious zero (‘0’) symbols. They provide redundant information.
Not sure whether GCC 15 complains or not.

Thanks.

Coly Li

Re: [PATCH] md/bcache: Mark __nonstring look-up table

[Ard Biesheuvel]

On Thu, 17 Apr 2025 at 15:12, Coly Li <i@coly.li> wrote:
>
>
>
> > 2025年4月17日 15:10，Kees Cook <kees@kernel.org> 写道：
> >
> >
> >
> > On April 16, 2025 11:16:45 PM PDT, Ard Biesheuvel <ardb@kernel.org> wrote:
> >> On Thu, 17 Apr 2025 at 00:01, Kees Cook <kees@kernel.org> wrote:
> >>>
> >>> 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 to silence the GCC warning.
> >>>
> >>> Signed-off-by: Kees Cook <kees@kernel.org>
> >>> ---
> >>> Cc: Coly Li <colyli@kernel.org>
> >>> Cc: Kent Overstreet <kent.overstreet@linux.dev>
> >>> Cc: linux-bcache@vger.kernel.org
> >>> ---
> >>> drivers/md/bcache/super.c | 2 +-
> >>> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> >>> index e42f1400cea9..577d048170fe 100644
> >>> --- a/drivers/md/bcache/super.c
> >>> +++ b/drivers/md/bcache/super.c
> >>> @@ -546,7 +546,7 @@ 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 = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
> >>>
> >>
> >> Just
> >>
> >> static const char zero_uuid[16] = {};
> >>
> >> should work fine here too. No need for the initializer.
> >
> > 🤦 Yes. This is what I get for fixing dozens of these. I'll send a v2...
>
>
> Can we do this,
>
> static const char zero_uuid[16] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
>
> I like the explicit array element number 16, and the explicit uuid content by obvious zero (‘0’) symbols. They provide redundant information.
> Not sure whether GCC 15 complains or not.
>

Even the {} initializer is entirely redundant, given that the variable
has static linkage, and so C guarantees that it will be zero
initialized.

Could you use NULL_GUID and be done with it?

Re: [PATCH] md/bcache: Mark __nonstring look-up table

[Coly Li]

> 2025年4月17日 22:08，Ard Biesheuvel <ardb@kernel.org> 写道：
> 
> On Thu, 17 Apr 2025 at 15:12, Coly Li <i@coly.li> wrote:
>> 
>> 
>> 
>>> 2025年4月17日 15:10，Kees Cook <kees@kernel.org> 写道：
>>> 
>>> 
>>> 
>>> On April 16, 2025 11:16:45 PM PDT, Ard Biesheuvel <ardb@kernel.org> wrote:
>>>> On Thu, 17 Apr 2025 at 00:01, Kees Cook <kees@kernel.org> wrote:
>>>>> 
>>>>> 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 to silence the GCC warning.
>>>>> 
>>>>> Signed-off-by: Kees Cook <kees@kernel.org>
>>>>> ---
>>>>> Cc: Coly Li <colyli@kernel.org>
>>>>> Cc: Kent Overstreet <kent.overstreet@linux.dev>
>>>>> Cc: linux-bcache@vger.kernel.org
>>>>> ---
>>>>> drivers/md/bcache/super.c | 2 +-
>>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>> 
>>>>> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
>>>>> index e42f1400cea9..577d048170fe 100644
>>>>> --- a/drivers/md/bcache/super.c
>>>>> +++ b/drivers/md/bcache/super.c
>>>>> @@ -546,7 +546,7 @@ 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 = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
>>>>> 
>>>> 
>>>> Just
>>>> 
>>>> static const char zero_uuid[16] = {};
>>>> 
>>>> should work fine here too. No need for the initializer.
>>> 
>>> 🤦 Yes. This is what I get for fixing dozens of these. I'll send a v2...
>> 
>> 
>> Can we do this,
>> 
>> static const char zero_uuid[16] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
>> 
>> I like the explicit array element number 16, and the explicit uuid content by obvious zero (‘0’) symbols. They provide redundant information.
>> Not sure whether GCC 15 complains or not.
>> 
> 
> Even the {} initializer is entirely redundant, given that the variable
> has static linkage, and so C guarantees that it will be zero
> initialized.
> 
> Could you use NULL_GUID and be done with it?

I feel the “static” here is an optimization to avoid initializing zero_uuid again ….

Kent,

Am I right?

Coly Li