Hi Arnd,
On Thu, Mar 7, 2019 at 9:01 AM Arnd Bergmann <a...@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 <a...@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.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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