[PATCH 1/1] Bluetooth: make hci_test_bit's addr const

[PATCH 1/1] Bluetooth: make hci_test_bit's addr const

[Jiri Slaby]

gcc5 warns about passing a const array to hci_test_bit which takes a
non-const pointer:
net/bluetooth/hci_sock.c: In function ‘hci_sock_sendmsg’:
net/bluetooth/hci_sock.c:955:8: warning: passing argument 2 of ‘hci_test_bit’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-array-qualifiers]
        &hci_sec_filter.ocf_mask[ogf])) &&
        ^
net/bluetooth/hci_sock.c:49:19: note: expected ‘void *’ but argument is of type ‘const __u32 (*)[4] {aka const unsigned int (*)[4]}’
 static inline int hci_test_bit(int nr, void *addr)
                   ^

So make 'addr' 'const void *'.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Marcel Holtmann <marcel@holtmann.org>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Johan Hedberg <johan.hedberg@gmail.com>
---
 net/bluetooth/hci_sock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/bluetooth/hci_sock.c b/net/bluetooth/hci_sock.c
index 1d65c5be7c82..34a095ff8679 100644
--- a/net/bluetooth/hci_sock.c
+++ b/net/bluetooth/hci_sock.c
@@ -46,7 +46,7 @@ struct hci_pinfo {
 	unsigned short    channel;
 };
 
-static inline int hci_test_bit(int nr, void *addr)
+static inline int hci_test_bit(int nr, const void *addr)
 {
 	return *((__u32 *) addr + (nr >> 5)) & ((__u32) 1 << (nr & 31));
 }
-- 
2.3.0

Re: [PATCH 1/1] Bluetooth: make hci_test_bit's addr const

[Jiri Slaby]

On 02/19/2015, 02:56 PM, Jiri Slaby wrote:
> gcc5 warns about passing a const array to hci_test_bit which takes a
> non-const pointer:
> net/bluetooth/hci_sock.c: In function ‘hci_sock_sendmsg’:
> net/bluetooth/hci_sock.c:955:8: warning: passing argument 2 of ‘hci_test_bit’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-array-qualifiers]
>         &hci_sec_filter.ocf_mask[ogf])) &&
>         ^
> net/bluetooth/hci_sock.c:49:19: note: expected ‘void *’ but argument is of type ‘const __u32 (*)[4] {aka const unsigned int (*)[4]}’
>  static inline int hci_test_bit(int nr, void *addr)
>                    ^
> 
> So make 'addr' 'const void *'.
> 
> Signed-off-by: Jiri Slaby <jslaby@suse.cz>
> Cc: Marcel Holtmann <marcel@holtmann.org>
> Cc: Gustavo Padovan <gustavo@padovan.org>
> Cc: Johan Hedberg <johan.hedberg@gmail.com>
> ---
>  net/bluetooth/hci_sock.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/bluetooth/hci_sock.c b/net/bluetooth/hci_sock.c
> index 1d65c5be7c82..34a095ff8679 100644
> --- a/net/bluetooth/hci_sock.c
> +++ b/net/bluetooth/hci_sock.c
> @@ -46,7 +46,7 @@ struct hci_pinfo {
>  	unsigned short    channel;
>  };
>  
> -static inline int hci_test_bit(int nr, void *addr)
> +static inline int hci_test_bit(int nr, const void *addr)
>  {
>  	return *((__u32 *) addr + (nr >> 5)) & ((__u32) 1 << (nr & 31));

quite interestingly, the compiler doesn't complain against the cast...
Will send a v2.

-- 
js
suse labs

[PATCH v2 1/1] Bluetooth: make hci_test_bit's addr const

[Jiri Slaby]

gcc5 warns about passing a const array to hci_test_bit which takes a
non-const pointer:
net/bluetooth/hci_sock.c: In function ‘hci_sock_sendmsg’:
net/bluetooth/hci_sock.c:955:8: warning: passing argument 2 of ‘hci_test_bit’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-array-qualifiers]
        &hci_sec_filter.ocf_mask[ogf])) &&
        ^
net/bluetooth/hci_sock.c:49:19: note: expected ‘void *’ but argument is of type ‘const __u32 (*)[4] {aka const unsigned int (*)[4]}’
 static inline int hci_test_bit(int nr, void *addr)
                   ^

So make 'addr' 'const void *'.

[v2] make the pointer in the cast const too. 

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Marcel Holtmann <marcel@holtmann.org>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Johan Hedberg <johan.hedberg@gmail.com>
---
 net/bluetooth/hci_sock.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/hci_sock.c b/net/bluetooth/hci_sock.c
index 1d65c5be7c82..d1a7d67619d8 100644
--- a/net/bluetooth/hci_sock.c
+++ b/net/bluetooth/hci_sock.c
@@ -46,9 +46,9 @@ struct hci_pinfo {
 	unsigned short    channel;
 };
 
-static inline int hci_test_bit(int nr, void *addr)
+static inline int hci_test_bit(int nr, const void *addr)
 {
-	return *((__u32 *) addr + (nr >> 5)) & ((__u32) 1 << (nr & 31));
+	return *((const __u32 *) addr + (nr >> 5)) & ((__u32) 1 << (nr & 31));
 }
 
 /* Security filter */
-- 
2.3.0

Re: [PATCH v2 1/1] Bluetooth: make hci_test_bit's addr const

[Marcel Holtmann]

Hi Jiri,

> gcc5 warns about passing a const array to hci_test_bit which takes a
> non-const pointer:
> net/bluetooth/hci_sock.c: In function ‘hci_sock_sendmsg’:
> net/bluetooth/hci_sock.c:955:8: warning: passing argument 2 of ‘hci_test_bit’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-array-qualifiers]
>        &hci_sec_filter.ocf_mask[ogf])) &&
>        ^
> net/bluetooth/hci_sock.c:49:19: note: expected ‘void *’ but argument is of type ‘const __u32 (*)[4] {aka const unsigned int (*)[4]}’
> static inline int hci_test_bit(int nr, void *addr)
>                   ^
> 
> So make 'addr' 'const void *'.
> 
> [v2] make the pointer in the cast const too. 
> 
> Signed-off-by: Jiri Slaby <jslaby@suse.cz>
> Cc: Marcel Holtmann <marcel@holtmann.org>
> Cc: Gustavo Padovan <gustavo@padovan.org>
> Cc: Johan Hedberg <johan.hedberg@gmail.com>
> ---
> net/bluetooth/hci_sock.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/bluetooth/hci_sock.c b/net/bluetooth/hci_sock.c
> index 1d65c5be7c82..d1a7d67619d8 100644
> --- a/net/bluetooth/hci_sock.c
> +++ b/net/bluetooth/hci_sock.c
> @@ -46,9 +46,9 @@ struct hci_pinfo {
> 	unsigned short    channel;
> };
> 
> -static inline int hci_test_bit(int nr, void *addr)
> +static inline int hci_test_bit(int nr, const void *addr)
> {
> -	return *((__u32 *) addr + (nr >> 5)) & ((__u32) 1 << (nr & 31));
> +	return *((const __u32 *) addr + (nr >> 5)) & ((__u32) 1 << (nr & 31));
> }

we had a lengthy discussion about this before. I am reluctant to change any of this until we have a test tool that proofs this does not break userspace API compatibility.

I don't see how just adding const would break anything, but I cautious since this code is pretty much a big mistake that we are carrying around for almost 14 years now.

Regards

Marcel

Re: [PATCH v2 1/1] Bluetooth: make hci_test_bit's addr const

[Jiri Slaby]

On 02/19/2015, 05:10 PM, Marcel Holtmann wrote:
> Hi Jiri,
> 
>> gcc5 warns about passing a const array to hci_test_bit which takes a
>> non-const pointer:
>> net/bluetooth/hci_sock.c: In function ‘hci_sock_sendmsg’:
>> net/bluetooth/hci_sock.c:955:8: warning: passing argument 2 of ‘hci_test_bit’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-array-qualifiers]
>>        &hci_sec_filter.ocf_mask[ogf])) &&
>>        ^
>> net/bluetooth/hci_sock.c:49:19: note: expected ‘void *’ but argument is of type ‘const __u32 (*)[4] {aka const unsigned int (*)[4]}’
>> static inline int hci_test_bit(int nr, void *addr)
>>                   ^
>>
>> So make 'addr' 'const void *'.
>>
>> [v2] make the pointer in the cast const too. 
>>
>> Signed-off-by: Jiri Slaby <jslaby@suse.cz>
>> Cc: Marcel Holtmann <marcel@holtmann.org>
>> Cc: Gustavo Padovan <gustavo@padovan.org>
>> Cc: Johan Hedberg <johan.hedberg@gmail.com>
>> ---
>> net/bluetooth/hci_sock.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/bluetooth/hci_sock.c b/net/bluetooth/hci_sock.c
>> index 1d65c5be7c82..d1a7d67619d8 100644
>> --- a/net/bluetooth/hci_sock.c
>> +++ b/net/bluetooth/hci_sock.c
>> @@ -46,9 +46,9 @@ struct hci_pinfo {
>> 	unsigned short    channel;
>> };
>>
>> -static inline int hci_test_bit(int nr, void *addr)
>> +static inline int hci_test_bit(int nr, const void *addr)
>> {
>> -	return *((__u32 *) addr + (nr >> 5)) & ((__u32) 1 << (nr & 31));
>> +	return *((const __u32 *) addr + (nr >> 5)) & ((__u32) 1 << (nr & 31));
>> }
> 
> we had a lengthy discussion about this before. I am reluctant to change any of this until we have a test tool that proofs this does not break userspace API compatibility.
> 
> I don't see how just adding const would break anything, but I cautious since this code is pretty much a big mistake that we are carrying around for almost 14 years now.

Yeah, I understand, but relying on the compiler is worse in this case, I
think. Here, the function casts away const from a const array, which is
undefined behaviour (6.7.3 of the standard).

So all in all I believe applying this fix cannot make the code worse.

thanks,
-- 
js
suse labs

Re: [PATCH v2 1/1] Bluetooth: make hci_test_bit's addr const

[Marcel Holtmann]

Hi Jiri,

> gcc5 warns about passing a const array to hci_test_bit which takes a
> non-const pointer:
> net/bluetooth/hci_sock.c: In function ‘hci_sock_sendmsg’:
> net/bluetooth/hci_sock.c:955:8: warning: passing argument 2 of ‘hci_test_bit’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-array-qualifiers]
>        &hci_sec_filter.ocf_mask[ogf])) &&
>        ^
> net/bluetooth/hci_sock.c:49:19: note: expected ‘void *’ but argument is of type ‘const __u32 (*)[4] {aka const unsigned int (*)[4]}’
> static inline int hci_test_bit(int nr, void *addr)
>                   ^
> 
> So make 'addr' 'const void *'.
> 
> [v2] make the pointer in the cast const too. 

btw. the version comments should go after the --- so that git am takes it back out. I do not need them in the commit message.

> 
> Signed-off-by: Jiri Slaby <jslaby@suse.cz>
> Cc: Marcel Holtmann <marcel@holtmann.org>
> Cc: Gustavo Padovan <gustavo@padovan.org>
> Cc: Johan Hedberg <johan.hedberg@gmail.com>
> ---
> net/bluetooth/hci_sock.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)

Patch has been applied to bluetooth-next tree.

Regards

Marcel

Re: [PATCH v2 1/1] Bluetooth: make hci_test_bit's addr const

[Marcel Holtmann]

Hi Jiri,

>>> gcc5 warns about passing a const array to hci_test_bit which takes a
>>> non-const pointer:
>>> net/bluetooth/hci_sock.c: In function ‘hci_sock_sendmsg’:
>>> net/bluetooth/hci_sock.c:955:8: warning: passing argument 2 of ‘hci_test_bit’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-array-qualifiers]
>>>       &hci_sec_filter.ocf_mask[ogf])) &&
>>>       ^
>>> net/bluetooth/hci_sock.c:49:19: note: expected ‘void *’ but argument is of type ‘const __u32 (*)[4] {aka const unsigned int (*)[4]}’
>>> static inline int hci_test_bit(int nr, void *addr)
>>>                  ^
>>> 
>>> So make 'addr' 'const void *'.
>>> 
>>> [v2] make the pointer in the cast const too. 
>>> 
>>> Signed-off-by: Jiri Slaby <jslaby@suse.cz>
>>> Cc: Marcel Holtmann <marcel@holtmann.org>
>>> Cc: Gustavo Padovan <gustavo@padovan.org>
>>> Cc: Johan Hedberg <johan.hedberg@gmail.com>
>>> ---
>>> net/bluetooth/hci_sock.c | 4 ++--
>>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>> 
>>> diff --git a/net/bluetooth/hci_sock.c b/net/bluetooth/hci_sock.c
>>> index 1d65c5be7c82..d1a7d67619d8 100644
>>> --- a/net/bluetooth/hci_sock.c
>>> +++ b/net/bluetooth/hci_sock.c
>>> @@ -46,9 +46,9 @@ struct hci_pinfo {
>>> 	unsigned short    channel;
>>> };
>>> 
>>> -static inline int hci_test_bit(int nr, void *addr)
>>> +static inline int hci_test_bit(int nr, const void *addr)
>>> {
>>> -	return *((__u32 *) addr + (nr >> 5)) & ((__u32) 1 << (nr & 31));
>>> +	return *((const __u32 *) addr + (nr >> 5)) & ((__u32) 1 << (nr & 31));
>>> }
>> 
>> we had a lengthy discussion about this before. I am reluctant to change any of this until we have a test tool that proofs this does not break userspace API compatibility.
>> 
>> I don't see how just adding const would break anything, but I cautious since this code is pretty much a big mistake that we are carrying around for almost 14 years now.
> 
> Yeah, I understand, but relying on the compiler is worse in this case, I
> think. Here, the function casts away const from a const array, which is
> undefined behaviour (6.7.3 of the standard).
> 
> So all in all I believe applying this fix cannot make the code worse.

lets give this a try then. Seems nobody is willing to write a test tool anyway.

Regards

Marcel