Re: [RFC v2] bpf.2: Use standard types and attributes

Florian Weimer
2021-05-04T19:45:25Z

* Alejandro Colomar:

> The thing is, in all of those threads, the only reasons to avoid
> <stdint.h> types in the kernel (at least, the only explicitly
> mentioned ones) are (a bit simplified, but this is the general idea of
> those threads):
>
> * Possibly breaking something in such a big automated change.
> * Namespace collision with userspace (the C standard allows defining
> uint32_t for nefarious purposes as long as you don't include
> <stdint.h>. POSIX prohibits that, though)
> * Uglier

__u64 can't be formatted with %llu on all architectures. That's not
true for uint64_t, where you have to use %lu on some architectures to
avoid compiler warnings (and technically undefined behavior). There are
preprocessor macros to get the expected format specifiers, but they are
clunky. I don't know if the problem applies to uint32_t. It does
happen with size_t and ptrdiff_t on 32-bit targets (both vary between
int and long).

Thanks,
Florian