Compiler printf format checking

Mikael Vidstedt mikael.vidstedt at
Thu Dec 12 19:12:56 PST 2013

I get this on Linux:

   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]


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
>> <mailto:john.r.rose at>> wrote:
>>> On Dec 11, 2013, at 2:41 PM, Dmitry Samersoff
>>> <dmitry.samersoff at <mailto:dmitry.samersoff at>> 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

More information about the hotspot-runtime-dev mailing list