| Message ID | 20190307104900.2506657-1-arnd@arndb.de |
|---|---|
| State | New |
| Headers | show |
| Series | [v3] dma-mapping: work around clang bug | expand |
NAK on this whole patch. Please fix the compiler instead of making a complete mess of a common macro.
On Fri, Mar 8, 2019 at 7:27 AM Christoph Hellwig <hch@lst.de> wrote: > > NAK on this whole patch. Please fix the compiler instead of making > a complete mess of a common macro. Definitely on the TODO list; higher priority, but not highest right now. I'll see if I can get some help with it. -- Thanks, ~Nick Desaulniers
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index 75e60be91e5f..5788d60c2223 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -138,7 +138,11 @@ 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)) +/* + * Shifting '2' instead of '1' because of + * https://bugs.llvm.org/show_bug.cgi?id=38789 + */ +#define DMA_BIT_MASK(n) (((n) == 0) ? 0ULL : (2ULL<<((n)-1))-1) #define DMA_MASK_NONE 0x0ULL
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 Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be> Reviewed-by: Robin Murphy <robin.murphy@arm.com> Signed-off-by: Arnd Bergmann <arnd@arndb.de> --- v3: use (2ull << n-1) instead of ((1ull << n-1) << 1) special-case 0 instead of 64 v2: fix off-by-one error --- include/linux/dma-mapping.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) -- 2.20.0