Compiler printf format checking

[Dmitry Samersoff]

Mikael,

With our own implementation of printf we can do whatever we whant - i.e.
add zero by default to all %p output.

With stock implementation (gnu_printf) - yes, we have to cast.

Personally, I have a long standing dream to get rid of all formatting
macros we have today - it makes code less readable.

-Dmitry



On 2013-12-13 23:05, Mikael Vidstedt wrote:
> 
> Dmitry,
> 
> Right, so unless I'm missing something that means we're back to adding
> casts in all the places we want zero padded pointer values (which today
> is the default when using PTR_FORMAT & friends)?
> 
> Cheers,
> Mikael
> 
> On 2013-12-13 01:14, Dmitry Samersoff wrote:
>> Mikael,
>>
>> Leading zero is not a part of C99 specification, so gcc warn about it.
>>
>> You can omit zero and in this case no extra warning happens.
>>
>>
>> Correct C99 way to print pointer with leading zeroes is
>>
>> printf("%08" PRIxPTR "\n", (uintptr_t)my_ptr);
>>
>> but we are loosing compiler warning.
>>
>>
>> -Dmitry
>>
>> On 2013-12-13 07:12, Mikael Vidstedt wrote:
>>> I get this on Linux:
>>>
>>> int
>>> main(void)
>>> {
>>>    printf("%08p", NULL);
>>>    return 0;
>>> }
>>>
>>> $ gcc -Wall -o tst tst.c
>>> tst.c: In function âmainâ:
>>> tst.c:6:3: warning: '0' flag used with â%pâ gnu_printf format [-Wformat]
>>>
>>> /Mikael
>>>
>>> On 2013-12-12 13:52, Dmitry Samersoff wrote:
>>>> On 2013-12-12 05:14, Mikael Vidstedt wrote:
>>>>> Are we saying the gcc format checking ignores any qualifiers on %p,
>>>>> yet
>>>>> correctly treats it as a pointer format? That is, if we use something
>>>>> like "%08p", will gcc still recognize that as a pointer format and
>>>>> look
>>>>> for a pointer argument (without complaining)?
>>>> Int arg:
>>>>
>>>> dooku:dms#cc test.c
>>>> test.c: In function ‘main’:
>>>> test.c:8:2: warning: format ‘%8p’ expects type ‘void *’, but argument 2
>>>> has type ‘int’
>>>>
>>>> Pointer arg compiles silently.
>>>>
>>>> -Dmitry
>>>>
>>>>> Cheers,
>>>>> Mikael
>>>>>
>>>>> On Dec 11, 2013, at 3:06 PM, John Rose <john.r.rose at oracle.com
>>>>> <mailto:john.r.rose at oracle.com>> wrote:
>>>>>
>>>>>> On Dec 11, 2013, at 2:41 PM, Dmitry Samersoff
>>>>>> <dmitry.samersoff at oracle.com <mailto:dmitry.samersoff at oracle.com>>
>>>>>> wrote:
>>>>>>
>>>>>>> we can just use %p on all platforms
>>>>>> That's clever.
>>>>>>
>>>>>> I do think we need to use an off-the-shelf static analyzer for the
>>>>>> format strings.  There is only a tiny amount of room to maneuver
>>>>>> within the confines of the language of printf format strings.
>>>>>>
>>>>>> There are probably several other fiddly details like this, such as
>>>>>> "how do I format intptr_t" and "how do I format jlong" and maybe "how
>>>>>> do I format an oop".  It may be possible to do some dodges like %p to
>>>>>> get around those also.  (The [-+#] modifiers look tantalizing to
>>>>>> me in
>>>>>> this regard.)
>>>>>>
>>>>>> — John
>>
> 


-- 
Dmitry Samersoff
Oracle Java development team, Saint Petersburg, Russia
* I would love to change the world, but they won't give me the sources.