define extern function printf style in ispc for logging

Question

I want to implement a debugging function for my ispc code that can take a logging level as an argument and then printf style string and arguments.

The signature would be something like:

extern "C" void debug_log(enumDebugLevel debugLevel, char *literalString, ...);

I can see that ispc doesn't support "Variable numbers of arguments to functions" neither does it support strings or the char data type so I am thinking that the chances are pretty limited.

However, there is a built in function called print that works with both string literals and variable argument count. I am wondering if there is a way to implement my function as an extern function even though ispc itself does not support these features.