Messages in this thread | | | From | Arnd Bergmann <> | Date | Thu, 7 Mar 2019 09:50:27 +0100 | Subject | Re: [PATCH] dma-mapping: work around clang bug |
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On Thu, Mar 7, 2019 at 9:28 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > On Thu, Mar 7, 2019 at 9:01 AM Arnd Bergmann <arnd@arndb.de> wrote: > > Clang has a rather annoying behavior of checking for integer > > arithmetic problems in code paths that are discarded by gcc > > before that perfoms the same checks. > > > > For DMA_BIT_MASK(64), this leads to a warning despite the > > result of the macro being completely sensible: > > > > arch/arm/plat-iop/adma.c:146:24: error: shift count >= width of type [-Werror,-Wshift-count-overflow] > > .coherent_dma_mask = DMA_BIT_MASK(64), > > > > The best workaround I could come up with is to shift the > > value twice, which makes the macro way less readable but > > always has the same result. > > > > Link: https://bugs.llvm.org/show_bug.cgi?id=38789 > > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > > --- > > include/linux/dma-mapping.h | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h > > index 75e60be91e5f..380d3a95d02e 100644 > > --- a/include/linux/dma-mapping.h > > +++ b/include/linux/dma-mapping.h > > @@ -138,7 +138,8 @@ struct dma_map_ops { > > extern const struct dma_map_ops dma_virt_ops; > > extern const struct dma_map_ops dma_dummy_ops; > > > > -#define DMA_BIT_MASK(n) (((n) == 64) ? ~0ULL : ((1ULL<<(n))-1)) > > +/* double shift to work around https://bugs.llvm.org/show_bug.cgi?id=38789 */ > > +#define DMA_BIT_MASK(n) (((n) == 64) ? ~0ULL : (((1ULL<<((n)-1))-1) << 1)) > > The second "-1" should be done on the final result, not on the > intermediate value.
Ah, of course. I'll send an update patch in a bit, sorry about this.
Arnd
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