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

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

quoted

__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