Re: What is the right way to print a UINTN?

[Laszlo Ersek <lersek@redhat.com>]

On 09/27/16 18:03, Cohen, Eugene wrote:
>> Printing UINTN with %x *or* with %d are equally bugs.
>>
>> For X64 / AARCH64 / IA64 builds, they are actual bugs (that happen to
>> work most of the time).
> 
> Feel free to file a Bugzilla on the extensive usage of this in edk2 [ducking and running].  :)

Not a bad idea, but it's not practical. I take care to use the right
casts and conversion specifiers whenever I write new code, but for
identifying existent incorrect calls, compiler support would be necessary.

I guess we could add the GCC function attribute that I mentioned earlier
to some of the PrintLib functions, and then address the resultant
warning messages. The problem is that some of the edk2-defined
conversion specifiers

- are not defined in standard (or GNU) C -- for example, %t --, which
might prevent GCC from pairing the corresponding argument with any
conversion specifier at all,

- and/or work differently from their standard (or GNU) C counterparts:
  - for example %g is entirely different between edk2 and standard C
    ((EFI_GUID *) vs. double),
  - the "L" length modifier is invalid for %x in standard C,
  - etc.

If someone is into GCC or CLANG plugin development, creating an "edk2
PrintLib" function attribute could be a good task :)

>>> I'm envisioning having to create a slide in the future for UEFI
>>> training about the proper use of UINTNs and describing "If you think
>>> it may exceed 2^32-1 then upcast to UINT64, otherwise don't worry
>>> about it" and it makes me squirm.
>>
>> It makes me squirm too. I think the slide should recommend the
>> casting
>> that I proposed. ;) "There is no conversion specifier dedicated to
>> UINTN; the portable way to print it is to cast it to UINT64, then print
>> it with %Lx."
> 
> This is reasonable although I expect to get asked why a lot of the other code doesn't adhere to this recommendation.

"Because people didn't realize it was a bug and it worked in practice"? :)

Thanks
Laszlo