RE: [PATCH v2] net: bluetooth: hci_sock: Use 'const void *' instead of 'void *' for 2nd parameter of hci_test_bit()

David Laight
2015-02-04T12:14:50Z

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