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    SubjectRe: I need help with a sparse warning
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    On Friday 12 September 2008, Larry Finger wrote:
    > Steven Noonan wrote:
    > > On Thu, Sep 11, 2008 at 7:13 PM, Larry Finger <Larry.Finger@lwfinger.net> wrote:
    > >> In file drivers/net/wireless/p54/p54common.c, the statement
    > >>
    > >> priv->rx_mtu = (size_t) le16_to_cpu((__le16)bootrec->data[10]);
    > >>
    > >> generates the sparse warning
    > >>
    > >> .../p54common.c:185:29: warning: cast to restricted __le16
    > >>
    > >> where bootrec->data is u32, and priv->rx_mtu is u16.
    > >>
    > >
    > > (Whoops, didn't CC the mailing lists. Sorry about the double-message, Larry.)
    > >
    > > If priv->rx_mtu is u16, I'm surprised it doesn't get noisy about the
    > > size_t cast. Unless the machine it's being compiled on is 16-bit, that
    > > should throw a truncation warning, because size_t should be a 32-bit
    > > integer on 32-bit machines (typically).
    > >
    > > I think if you change the (__le16) cast to (__le16 __force) it will
    > > stop warning you about that particular issue.
    >
    > This one gets rid of the sparse warning.
    >
    > priv->rx_mtu = le16_to_cpu((__le16 __force)
    > bootrec->data[10]);

    I think you should rather fix the type of bootrec->data.
    If it is u32, but the data in fact is __le16, please fix the struct instead
    of adding dangerous casts.
    Note that this is especially dangerous, because you cast between different
    typesizes and endianesses at the same time.


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