Re: [PATCH v2] bitops: Fix shift overflow in GENMASK macros

[Peter Zijlstra]

On Tue, Nov 04, 2014 at 11:03:57AM +0100, Maxime COQUELIN wrote:

> -#define GENMASK(h, l)		(((U32_C(1) << ((h) - (l) + 1)) - 1) << (l))
> -#define GENMASK_ULL(h, l)	(((U64_C(1) << ((h) - (l) + 1)) - 1) << (l))
> +#define GENMASK(h, l)     ((~0UL >> (BITS_PER_LONG - (h - l + 1))) << l)
> +#define GENMASK_ULL(h, l) ((~0ULL >> (BITS_PER_LONG_LONG - (h - l + 1))) << l)

OK, so you need to keep the (h) and (l) bits, macro arguments should be
wrapped in seemingly superfluous braces in order to preserve precedence
on expansion.

My bad for not explicitly doing that when suggesting the alternative.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/