int debug_fprintf(DEBUG_FILE *stream, const char *format, ...);
debug_fprintf writes to stream, under control of the string pointed to by format that specifies how subsequent arguments are converted for output. The format string is a standard C printf format string. The actual formatting is performed on the host by the debugger and therefore debug_fprintf consumes only a very small amount of code and data space, only the overhead to call the function.
If there are insufficient arguments for the format, the behavior is undefined. If the format is exhausted while arguments remain, the excess arguments are evaluated but are otherwise ignored.
debug_fprintf returns the number of characters transmitted, or a negative value if an output or encoding error occurred.