On Fri, Feb 04, 2022 at 10:39:46AM +0100, Vitaly Kuznetsov wrote: > Vitaly Chikunov <vt@xxxxxxxxxxxx> 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. This is already known. I dealt with a similar report before. At the time I decided nothing's wrong with the code. https://lore.kernel.org/linux-kernel/YcC1CobR%2Fn0tJhdV@archlinux-ax161/ https://github.com/ClangBuiltLinux/linux/issues/92 I can certainly live with a workaround like this. > > > > > Cc: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx> > > Cc: Michael Kelley <mikelley@xxxxxxxxxxxxx> > > Cc: Long Li <longli@xxxxxxxxxxxxx> > > Cc: Wei Liu <wei.liu@xxxxxxxxxx> > > Link: https://lore.kernel.org/linux-hyperv/20220203235828.hcsj6najsl7yxmxa@xxxxxxxxxxxx/ > > Signed-off-by: Vitaly Chikunov <vt@xxxxxxxxxxxx> > > --- > > 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); Please add a comment here // Use ~0ULL instead of DMA_BIT_MASK(64) to work around a bug in Clang. > > +static u64 vmbus_dma_mask = ~0ULL; > > /* > > * vmbus_device_register - Register the child device > > */ > > -- > Vitaly >
