Re: [PATCH] usb: acpi: Fix shifting 31 bits

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Mar 18, 2021 at 10:14:30AM +0800, jiangzhipeng wrote:
> On Wed, 17 Mar 2021 15:51:02 +0100
> Greg KH <gregkh@linuxfoundation.org> wrote:
> 
> > On Wed, Mar 17, 2021 at 10:25:13PM +0800, jzp0409 wrote:
> > > From: "edison.jiang" <jiangzhipeng@yulong.com>
> > > 
> > > Fix undefined behaviour in the usb apci driver by using 'BIT'
> > > marcro.  
> > 
> > What is undefined about it?
> > 
> > > 
> > > Signed-off-by: edison.jiang <jiangzhipeng@yulong.com>  
> > 
> > This name is not a valid signed-off-by name (I doubt you sign
> > documents with a ".", right?) and it does not match the "From:" name
> > either, so something needs to be fixed before this patch could be
> > accepted.
> > 
> > > ---
> > >  drivers/usb/core/usb-acpi.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/usb/core/usb-acpi.c
> > > b/drivers/usb/core/usb-acpi.c index 50b2fc7..3e467a8 100644
> > > --- a/drivers/usb/core/usb-acpi.c
> > > +++ b/drivers/usb/core/usb-acpi.c
> > > @@ -122,7 +122,7 @@ static enum usb_port_connect_type
> > > usb_acpi_get_connect_type(acpi_handle handle,
> > >   * Private to usb-acpi, all the core needs to know is that
> > >   * port_dev->location is non-zero when it has been set by the
> > > firmware. */
> > > -#define USB_ACPI_LOCATION_VALID (1 << 31)
> > > +#define USB_ACPI_LOCATION_VALID BIT(31)  
> > 
> > I do not understand what this is trying to fix, please be more
> > specific.
> > 
> > thanks,
> > 
> > greg k-h
> 
> cppcheck error:
> linux/drivers/usb/core/usb-acpi.c:191]: (error) Shifting signed 32-bit
> value by 31 bits is undefined behaviour
> 

That does not explain anything, sorry.

greg k-h