md/bcache: Mark __nonstring look-up table

PATCH Superseded Kees Cook 3 participants 7 messages Apr 16, 2025 – Apr 17, 2025 bcache (block layer cache)

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Kees Cook

author

2025-04-16 22:01 UTC #0 lore raw

PATCH 1/1 md/bcache: Mark __nonstring look-up table

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 <[email protected]>

---
Cc: Coly Li <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: [email protected]

---
 drivers/md/bcache/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

drivers/md/bcache/super.c +1 -1

index e42f1400cea9..577d048170fe 100644
@@ -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);
 }

Signature · 1 line

2.34.1

Coly Li

2025-04-17 04:13 UTC #1 lore raw

Quoted 13 lines

2025年4月17日 06:01，Kees Cook <[email protected]> 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";
     |                                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Quoted 7 lines

Add the annotation to silence the GCC warning.
Signed-off-by Kees Cook <[email protected]>
---
Cc: Coly Li <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: [email protected] <mailto:[email protected]>

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

Coly Li

Quoted 21 lines

---
drivers/md/bcache/super.c | 2 +-

1 file changed, 1 insertion(+), 1 deletion(-)

drivers/md/bcache/super.c +1 -1

index e42f1400cea9..577d048170fe 100644
@@ -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);
 }

Signature · 1 line

2.34.1

Ard Biesheuvel

2025-04-17 06:16 UTC #2 lore raw

In reply to Kees Cook

Quoted 26 lines · 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 <[email protected]>
---
Cc: Coly Li <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: [email protected]
---
 drivers/md/bcache/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
drivers/md/bcache/super.c +0 -0
index e42f1400cea9..577d048170fe 100644

drivers/md/bcache/super.c static struct uuid_entry *uuid_find(struct cache_set *c, const char *uuid) · line 550

Quoted 6 lines

drivers/md/bcache/super.c +1 -1

@@ -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.

Quoted 6 lines

drivers/md/bcache/super.c +0 -1
        return uuid_find(c, zero_uuid);
 }
--
2.34.1

Kees Cook

author

2025-04-17 07:10 UTC #3 lore raw

Quoted 36 lines · Ard Biesheuvel

Quoted 26 lines · 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 <[email protected]>
---
Cc: Coly Li <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: [email protected]
---
 drivers/md/bcache/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
drivers/md/bcache/super.c +0 -0
index e42f1400cea9..577d048170fe 100644
drivers/md/bcache/super.c static struct uuid_entry *uuid_find(struct cache_set *c, const char *uuid) · line 550
Quoted 6 lines
drivers/md/bcache/super.c +1 -1
@@ -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

Quoted 3 lines

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

Signature · 1 line

Kees Cook

Coly Li

2025-04-17 13:50 UTC #4 lore raw

Quoted 43 lines

2025年4月17日 15:10，Kees Cook <[email protected]> 写道：
Quoted 36 lines · Ard Biesheuvel
Quoted 26 lines · 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 <[email protected]>
---
Cc: Coly Li <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: [email protected]
---
drivers/md/bcache/super.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
drivers/md/bcache/super.c +0 -0
index e42f1400cea9..577d048170fe 100644
drivers/md/bcache/super.c static struct uuid_entry *uuid_find(struct cache_set *c, const char *uuid) · line 550
Quoted 6 lines
drivers/md/bcache/super.c +1 -1
@@ -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

Quoted 5 lines

Quoted 3 lines
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

Ard Biesheuvel

2025-04-17 14:08 UTC #5 lore raw

Quoted 51 lines · Coly Li

Quoted 44 lines
2025年4月17日 15:10，Kees Cook <[email protected]> 写道：
Quoted 36 lines · Ard Biesheuvel
Quoted 26 lines · 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 <[email protected]>
---
Cc: Coly Li <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: [email protected]
---
drivers/md/bcache/super.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
drivers/md/bcache/super.c +0 -0
index e42f1400cea9..577d048170fe 100644
drivers/md/bcache/super.c static struct uuid_entry *uuid_find(struct cache_set *c, const char *uuid) · line 550
Quoted 6 lines
drivers/md/bcache/super.c +1 -1
@@ -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
Quoted 5 lines
Quoted 3 lines
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...

Quoted 7 lines

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?

Coly Li

2025-04-17 14:17 UTC #6 lore raw

Quoted 64 lines

2025年4月17日 22:08，Ard Biesheuvel <[email protected]> 写道：
Quoted 51 lines · Coly Li
Quoted 44 lines
2025年4月17日 15:10，Kees Cook <[email protected]> 写道：
Quoted 36 lines · Ard Biesheuvel
Quoted 26 lines · 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 <[email protected]>
---
Cc: Coly Li <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: [email protected]
---
drivers/md/bcache/super.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
drivers/md/bcache/super.c +0 -0
index e42f1400cea9..577d048170fe 100644
drivers/md/bcache/super.c static struct uuid_entry *uuid_find(struct cache_set *c, const char *uuid) · line 550
Quoted 6 lines
drivers/md/bcache/super.c +1 -1
@@ -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
Quoted 5 lines
Quoted 3 lines
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...
Quoted 7 lines
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.

Quoted 5 lines

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