[cfe-dev] vprintf(3) and "format string is not a string literal"

Ted Kremenek kremenek at apple.com
Mon Dec 17 11:07:36 PST 2007

On Dec 17, 2007, at 9:30 AM, Ted Kremenek wrote:

> On Dec 17, 2007, at 7:19 AM, Holger Schurig wrote:
>> I'm not subscribed to clang mailing list, so not sure if my mail
>> comes throught. I'm reading the list via gmane.
>> I guess utilizing gcc  __attribute__((format(...))) would help
>> here. You could put that at the log
>> int logmessage(
>> 	int loglevel,
>> 	char const *fmt __attribute__ (format (printf, 2, 3))),
>> 	...) {
>>  // more code
>> }
>> That way the compiler knows that fmt *IS* a format string and
>> won't need to warn when it is used in vprintf().
>> Code that calls logmessage() would know that fmt is a printf-like
>> format string and can check calls to logmessage. This attribute
>> would even help in the case of call-backs.
> I like this solution.  I think this would catch 90% of the correct
> cases, while suppressing most bogus messages.

I just committed patch r45114 that partially implements this solution:


Our support for attributes is still only preliminary, so right now I  
have coded the format string checker to not emit a warning if the  
format string for a vprintf-like function comes from the function  
parameter of the caller.  Later I will add the support to consult the  
attributes of the calling function to see if it should be treated like  
a printf function.
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