Re: [wireless-next:master 70/102] drivers/net/wireless/b43/phy_ht.c:338:35: sparse: cast truncates bits from constant value (ffff3fff becomes 3fff)

Re: [wireless-next:master 70/102] drivers/net/wireless/b43/phy_ht.c:338:35: sparse: cast truncates bits from constant value (ffff3fff becomes 3fff)

[Fengguang Wu]

I could disable this warning in my reports, but CC sparse authors
first to check if there are more elegant solutions.

On Mon, Sep 15, 2014 at 11:16:09PM +0200, Rafał Miłecki wrote:
> On 15 September 2014 21:50, kbuild test robot <fengguang.wu@intel.com> wrote:
> > tree:   git://git.kernel.org/pub/scm/linux/kernel/git/linville/wireless-next.git master
> > head:   1030f9fe65602465a89beaa05c3343cf9fd68a88
> > commit: 1f21de53ac8651b1a3e79576f1adf00aabecd052 [70/102] b43: HT-PHY: Implement band switching
> > reproduce:
> >   # apt-get install sparse
> >   git checkout 1f21de53ac8651b1a3e79576f1adf00aabecd052
> >   make ARCH=x86_64 allmodconfig
> >   make C=1 CF=-D__CHECK_ENDIAN__
> >
> >
> > sparse warnings: (new ones prefixed by >>)
> >
> >>> drivers/net/wireless/b43/phy_ht.c:338:35: sparse: cast truncates bits from constant value (ffff3fff becomes 3fff)
> >
> > vim +338 drivers/net/wireless/b43/phy_ht.c
> 
> I already got the same sparse warning twice (for different parts of code):
> 
> Message-ID: <53b5ab1e.Y9bKd3t4DteE6Pzc%fengguang.wu@intel.com>
> [wireless-next:master 163/164]
> drivers/net/wireless/b43/phy_n.c:5671:55: sparse: cast truncates bits
> from constant value (ffff7fff becomes 7fff)
> 
> Message-ID: <53c97150.9C2t3ebOTkndUZD5%fengguang.wu@intel.com>
> [wireless-next:master 70/75] drivers/net/wireless/b43/phy_n.c:6077:35:
> sparse: cast truncates bits from constant value (ffff3fff becomes
> 3fff)
> 
> In both of them I pointed that this is an expected behavior. No other
> solution was proposed.
> 
> Can this test be fixed or disabled?
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Re: [wireless-next:master 70/102] drivers/net/wireless/b43/phy_ht.c:338:35: sparse: cast truncates bits from constant value (ffff3fff becomes 3fff)

[Dan Carpenter]

On Tue, Sep 16, 2014 at 10:17:18AM +0800, Fengguang Wu wrote:
> I could disable this warning in my reports, but CC sparse authors
> first to check if there are more elegant solutions.

int main(void)
{
        printf("%x\n", (unsigned short)~(0xc00));   // <-- ok
        printf("%x\n", (unsigned short)~(0xc000));  // <-- complains

        return 0;
}

test.c:10:40: warning: cast truncates bits from constant value (ffff3fff becomes 3fff)

The reason the first one is ok is because we don't complain if the
truncated bits are purely sign bits.  I feel like it should apply to the
second statement as well.  If we're only masking out 0xffff then don't
complain.

regards,
dan carpenter