[dxuh]

Afaik the kernel is built as C89 and uintptr_t was introduced in C99.

[dataflow]

Damn. I'd have they they could just typedef it manually, but interesting, thanks.

[caf]

It's not even about how the kernel is built. The userspace-side system call declarations need to be #include-able in C89 user code, so they can't use C99 types.