linux-kernel - Re: [PATCH] staging/comedi/dt282x: avoid integer overflow warning

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Date:	Tue, 15 Mar 2016 22:50:16 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Hartley Sweeten <HartleyS@...ionengravers.com>
Cc:	Ian Abbott <abbotti@....co.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Amitoj Kaur Chawla <amitoj1606@...il.com>,
	Bhaktipriya Shridhar <bhaktipriya96@...il.com>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] staging/comedi/dt282x: avoid integer overflow warning

On Tuesday 15 March 2016 21:35:40 Hartley Sweeten wrote:
> On Monday, March 14, 2016 3:48 PM, Arnd Bergmann wrote:
> > gcc-6 warns about passing negative signed integer into swab16()
> > in the dt282x driver:
> 
> <snip>
> 
> > The warning makes sense, though the code is correct as far as I
> > can tell.
> >
> > This disambiguates the operation by making the constant expressions
> > we pass here explicitly 'unsigned', which helps to avoid the warning.
> >
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > ---
> >  drivers/staging/comedi/drivers/dt282x.c | 62 ++++++++++++++++-----------------
> >  1 file changed, 31 insertions(+), 31 deletions(-)
> >
> > diff --git a/drivers/staging/comedi/drivers/dt282x.c b/drivers/staging/comedi/drivers/dt282x.c
> > index 40bf00984fa5..d4d45c759c62 100644
> > --- a/drivers/staging/comedi/drivers/dt282x.c
> > +++ b/drivers/staging/comedi/drivers/dt282x.c
> > @@ -69,48 +69,48 @@
> >   * Register map
> >   */
> >  #define DT2821_ADCSR_REG		0x00
> > -#define DT2821_ADCSR_ADERR		(1 << 15)
> > -#define DT2821_ADCSR_ADCLK		(1 << 9)
> > -#define DT2821_ADCSR_MUXBUSY		(1 << 8)
> > -#define DT2821_ADCSR_ADDONE		(1 << 7)
> > -#define DT2821_ADCSR_IADDONE		(1 << 6)
> > +#define DT2821_ADCSR_ADERR		(1u << 15)
> 
> Changing all of these to use the BIT() macro should also avoid the warning.

Yes, but it won't work for the ones that have more than one bit:

#define DT2821_SUPCSR_DS_AD_TRIG       (3 << 10)

I considered using BIT() but decided against it for consistency.

	Arnd