linux-kernel - Re: I need help with a sparse warning

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Message-ID: <48C9DACE.5040308@lwfinger.net>
Date:	Thu, 11 Sep 2008 21:58:22 -0500
From:	Larry Finger <Larry.Finger@...inger.net>
To:	Steven Noonan <steven@...inklabs.net>
CC:	LKML <linux-kernel@...r.kernel.org>,
	wireless <linux-wireless@...r.kernel.org>
Subject: Re: I need help with a sparse warning

Steven Noonan wrote:
> On Thu, Sep 11, 2008 at 7:13 PM, Larry Finger <Larry.Finger@...inger.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]);

Thanks,

Larry
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