linux-kernel - Re: [PATCH v2 1/1] Bluetooth: make hci_test

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Message-Id: <A83B3719-29ED-4865-B16C-A82611177BF8@holtmann.org>
Date:	Fri, 27 Feb 2015 09:32:30 -0800
From:	Marcel Holtmann <marcel@...tmann.org>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	Johan Hedberg <johan.hedberg@...il.com>,
	BlueZ development <linux-bluetooth@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Gustavo F. Padovan" <gustavo@...ovan.org>
Subject: Re: [PATCH v2 1/1] Bluetooth: make hci_test_bit's addr const

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@...e.cz>
>>> Cc: Marcel Holtmann <marcel@...tmann.org>
>>> Cc: Gustavo Padovan <gustavo@...ovan.org>
>>> Cc: Johan Hedberg <johan.hedberg@...il.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

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