Re: [PATCH v2] drivers: hv: vmbus: Fix build on Clang 12 failed by DMA_BIT_MASK(64) expansion

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Vitaly Chikunov <vt@altlinux.org> writes:

> Clang 12.0.1 cannot understand that value 64 is excluded from the shift
> at compile time (for use in global context) 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.

Was this reported to Clang already? It looks like a clear bug on their side.

>
> 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>
> ---
> Changes since v1:
> - Patch description updated, s/GCC 11/Clang 12/.
>
>  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
>   */

-- 
Vitaly