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

Joseph Myers
2021-05-05T22:22:26Z

On Wed, 5 May 2021, David Laight via Libc-alpha wrote:

> > __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).
>
> uint32_t can be 'randomly' either int or long on typical 32bit architectures.
> The correct way to print it is with eg "xxx %5.4" PRI_u32 " yyy".

C2X adds printf length modifiers such as "w32", so you can use a
friendlier %w32u, for example. (Not yet implemented in glibc or in GCC's
format checking.)

--
Joseph S. Myers
joseph@codesourcery.com