linux-kernel - Re: [PATCH] rtl2832: remove compiler warning

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Date:	Wed, 11 Feb 2015 11:13:50 +0000
From:	Luis de Bethencourt <luis@...ethencourt.com>
To:	Mauro Carvalho Chehab <mchehab@....samsung.com>
Cc:	Antti Palosaari <crope@....fi>, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rtl2832: remove compiler warning

On Tue, Feb 10, 2015 at 09:35:52PM -0200, Mauro Carvalho Chehab wrote:
> Em Tue, 10 Feb 2015 12:57:24 +0200
> Antti Palosaari <crope@....fi> escreveu:
> 
> > On 02/09/2015 12:44 AM, Luis de Bethencourt wrote:
> > > Cleaning the following compiler warning:
> > > rtl2832.c:703:12: warning: 'tmp' may be used uninitialized in this function
> > >
> > > Even though it could never happen since if rtl2832_rd_demod_reg () doesn't set
> > > tmp, this line would never run because we go to err. It is still nice to avoid
> > > compiler warnings.
> > >
> > > Signed-off-by: Luis de Bethencourt <luis.bg@...sung.com>
> > > ---
> > >   drivers/media/dvb-frontends/rtl2832.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/media/dvb-frontends/rtl2832.c b/drivers/media/dvb-frontends/rtl2832.c
> > > index 5d2d8f4..ad36d1c 100644
> > > --- a/drivers/media/dvb-frontends/rtl2832.c
> > > +++ b/drivers/media/dvb-frontends/rtl2832.c
> > > @@ -685,7 +685,7 @@ static int rtl2832_read_status(struct dvb_frontend *fe, fe_status_t *status)
> > >   	struct rtl2832_dev *dev = fe->demodulator_priv;
> > >   	struct i2c_client *client = dev->client;
> > >   	int ret;
> > > -	u32 tmp;
> > > +	u32 tmp = 0;
> > >
> > >   	dev_dbg(&client->dev, "\n");
> > 
> > I looked the code and I cannot see how it could used as uninitialized. 
> > Dunno how it could be fixed properly.
> > 
> > Also, I think idiom to say compiler that variable could be uninitialized 
> > is to store its own value. But I am fine with zero initialization too.
> > 
> > u32 tmp = tmp;
> 
> Actually, the right way is to declare it as:
> 
> 	u32 uninitialized_var(tmp)
> 
> The syntax to suppress compiler warnings depends on the compiler:
> 
> include/linux/compiler-clang.h:#define uninitialized_var(x) x = *(&(x))
> include/linux/compiler-gcc.h:#define uninitialized_var(x) x = x
> 
> Also, using uninitialized_var() better documents it.
> 
> Regards,
> Mauro

Hi Mauro,

That is a way more elegant solution. Great!
I will check out that compiler-clang header file, it's interesting.

I just sent a revised patch using this :)

Thanks,
Luis
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