Re: [PATCH 4/4] asm-generic/bitsperlong.h: Add sanity checks for __BITS_PER_LONG

[Arnd Bergmann]

On Fri, Jan 16, 2026, at 08:40, Thomas Weißschuh wrote:
> The value of __BITS_PER_LONG from architecture-specific logic should
> always match the generic one if that is available. It should also match
> the actual C type 'long'.
>
> Mismatches can happen for example when building the compat vDSO. Either
> during the compilation, see commit 9a6d3ff10f7f ("arm64: uapi: Provide
> correct __BITS_PER_LONG for the compat vDSO"), or when running sparse
> when mismatched CHECKFLAGS are inherited from the kernel build.
>
> Add some consistency checks which detect such issues early and clearly.
> The tests are added to the UAPI header to make sure it is also used when
> building the vDSO as that is not supposed to use regular kernel headers.
>
> The kernel-interal BITS_PER_LONG is not checked as it is derived from
> CONFIG_64BIT and therefore breaks for the compat vDSO. See the similar,
> deactivated check in include/asm-generic/bitsperlong.h.
>
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>

Acked-by: Arnd Bergmann <arnd@xxxxxxxx>