Re: [PATCH V3 1/2] uapi: Define GENMASK_U128

[Arnd Bergmann]

On Tue, Aug 20, 2024, at 03:25, Anshuman Khandual wrote:
> On 8/19/24 12:43, Arnd Bergmann wrote:
>
> Should not the second shift operation warn about the possible
> overflow scenario ? But actually it does not. Or the compiler
> is too smart in detecting what's happening next in the overall
> equation and do the needful while creating the mask below the
> highest bit.

Not sure about the reasoning behind the compiler warning for
one but not the other, but I know that we rely on similar
behavior in places like:

#define upper_32_bits(n) ((u32)(((n) >> 16) >> 16))

which is intended to return a zero without a compiler
warning when passing an 'unsigned long' input on 32-bit
architectures.

      Arnd