Safer vararg calls

[Yair Lenga <yair.lenga@gmail.com>]

Hi,

Looking for feedback on the adding new attribute to function calls that will help create safer vararg functions.

Consider the case where a vararg function takes list of arguments of the same type. In my case, there are terminated with a sentinel of null.

Char *result = delimitedstr(‘:’ “foo”, “bar”, “zoo”, NULL) ;

The standard prototype
is char * delimitedstr(char delim, char *p1…) ;

Which will currently allow many incorrect calls:
 delimitedstr(‘:’, “foo”, 5, 7.3, ‘a’) ;    // bad types + missing sentinel.

The __attribute__((sentinel)) can force the last arg to be null.

My proposal is to add new attribute ((va_vector)) that will add a check that all parameters in a vararg list match the typeof the last parameter. So that:

__attribute__ ((va_typed)) delimitedstr(char delim, char *p1…) ;

Will flag a call where any of the parameter after p1, is not a string.

This can result in cleaner, safer code, without making the calling sequence more difficult, or modifying the behavior of the call.

For Java developers, this is basically the same type checking provided by the as ‘datatype …’ (without the conversion into array).

I am Looking for feedback, Pointers on how to implement, as I do not have experience with extending gcc.

Yair