linux-kernel - RE: [PATCH v2] net: bluetooth: hci_sock: Use 'const void *' instead of 'void *' for 2nd parameter of hci_test

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1CADA609@AcuExch.aculab.com>
Date:	Wed, 4 Feb 2015 12:13:56 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Chen Gang S' <gang.chen@...rus.com.cn>,
	Joe Perches <joe@...ches.com>
CC:	"marcel@...tmann.org" <marcel@...tmann.org>,
	"gustavo@...ovan.org" <gustavo@...ovan.org>,
	"johan.hedberg@...il.com" <johan.hedberg@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	"linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] net: bluetooth: hci_sock: Use 'const void *' instead
 of 'void *' for 2nd parameter of hci_test_bit()

From: Gang S
> On 2/3/15 10:32, Chen Gang S wrote:
> > On 2/3/15 05:20, Joe Perches wrote:
> >> On Tue, 2015-02-03 at 05:14 +0800, Chen Gang S wrote:
> >>> hci_test_bit() does not modify 2nd parameter, so it is better to let it
> >>> be constant, or may cause build warning. The related warning (with
> >>> allmodconfig under xtensa):
> >> []
> >>> diff --git 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));
> >>>  }
> >>
> >> It's probably better to use const __u32 * here too, but the
> >> real thing I wonder is whether or not there's an issue with
> >> one of the 2 uses of this function.
> >>
> >> One of them passes a unsigned long *, the other a u32 *.
> >>
> >> $ git grep -w hci_test_bit
> >> net/bluetooth/hci_sock.c:static inline int hci_test_bit(int nr, void *addr)
> >> net/bluetooth/hci_sock.c:       if (!hci_test_bit(flt_event, &flt->event_mask))
> >> net/bluetooth/hci_sock.c:                    !hci_test_bit(ocf & HCI_FLT_OCF_BITS,
> >> net/bluetooth/hci_sock.c-                                  &hci_sec_filter.ocf_mask[ogf])) &&
> >>
> >> hci_sec_filter.ocf_mask is __u32
> >> but flt->event_mask is unsigned long.
> >>
> >> Any possible issue here on 64-bit systems?
> >>
> >
> > For me, it can not cause issue on 64-bit systems. hci_test_bit() treats
> > 'addr' as "__u32 *", and has to use the pointer to do something.
> >
> 
> 'event_mask' is intended to type cast to "__u32 *" within 'hci_sock.c'.
> So for me, "const __u32 *" is better than "const void *" for 2nd
> parameter of hci_test_bit().
> 
> If what I said above is correct, and also if necessary, I shall patch v3
> for it.

How are the bits set in the first place?
If the array is ever indexed as long [] then the code above is unlikely
to be testing the correct bits.

	David

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