Re: [PATCH] drivers: hv: vmbus: Fix build on GCC 11 failed by DMA_BIT_MASK(64) expansion

[Vitaly Chikunov <vt@altlinux.org>]

Michael,

On Fri, Feb 04, 2022 at 01:48:32AM +0000, Michael Kelley (LINUX) wrote:
> From: Vitaly Chikunov <vt@altlinux.org>   Sent: Thursday, February 3, 2022 4:58 PM
> > 
> > GCC 11.2.1 cannot understand that value 64 is excluded from the shift
> > at compile time resulting in build error[1]:
> > 
> >   drivers/hv/vmbus_drv.c:2082:29: error: shift count >= width of type [-Werror,-
> > Wshift-count-overflow]
> >   static u64 vmbus_dma_mask = DMA_BIT_MASK(64);
> >                               ^~~~~~~~~~~~~~~~
> >   ./include/linux/dma-mapping.h:76:54: note: expanded from macro 'DMA_BIT_MASK'
> >   #define DMA_BIT_MASK(n) (((n) == 64) ? ~0ULL : ((1ULL<<(n))-1))
> >                                                        ^ ~~~
> > 
> > Avoid using DMA_BIT_MASK macro for that corner case.
> 
> If we need a temporary hack to solve the build problem, I can live with
> that.  But I see 230 other places in kernel code where DMA_BIT_MASK(64)
> is used, so I'm wondering if this particular hack is effective.  We need a
> more comprehensive solution that fixes the definition of
> DMA_BIT_MASK() so it will work with a constant '64' as the parameter.

Ah, I suddenly realised that this build was using Clang 12.0.1, not GCC
11. So my patch description is wrong!

Thanks,

> 
> Michael
> 
> > 
> > Cc: Tianyu Lan <Tianyu.Lan@microsoft.com>
> > Cc: Michael Kelley <mikelley@microsoft.com>
> > Cc: Long Li <longli@microsoft.com>
> > Cc: Wei Liu <wei.liu@kernel.org>
> > Link: https://lore.kernel.org/linux-hyperv/20220203235828.hcsj6najsl7yxmxa@altlinux.org/
> > Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
> > ---
> >  drivers/hv/vmbus_drv.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> > index 17bf55fe3169..2376ee484362 100644
> > --- a/drivers/hv/vmbus_drv.c
> > +++ b/drivers/hv/vmbus_drv.c
> > @@ -2079,7 +2079,7 @@ struct hv_device *vmbus_device_create(const guid_t *type,
> >         return child_device_obj;
> >  }
> > 
> > -static u64 vmbus_dma_mask = DMA_BIT_MASK(64);
> > +static u64 vmbus_dma_mask = ~0ULL;
> >  /*
> >   * vmbus_device_register - Register the child device
> >   */
> > --
> > 2.33.0