Re: Sparse not supporting kzalloc_obj() and friends

On Mon, 23 Feb 2026 at 02:52, Ricardo Ribalda <[email protected]> wrote:
>
> The culprit seems to be the new kzalloc_obj and friends.

Argh. The culprit is the use of __VA_OPT__, which apparently sparse
never got taught.

We already use __VA_OPT__ elsewhere in the kernel, but it's fairly
rare, so it apparently hasn't been noticed much. For example, btrfs
uses it, but apparently only under CONFIG_BTRFS_ASSERT

The btrfs use has a comment about _why_ the use of __VA_OPT__ is
actually needed:

 * As ##__VA_ARGS__ cannot be at the beginning of the macro the
__VA_OPT__ is needed
 * and supported since GCC 8 and Clang 12.

and that's why I used it in the new alloc_obj helpers too - not only
is it the more modern "standard C"  model, it's actually a bit more
user friendly than the traditional ## gcc trick.

Ho humm. I guess I should look at the sparse pre-processor code,
unless somebody already implemented __VA_OPT__ somewhere?

             Linus