-extern void sptps_log_quiet(sptps_t *s, int s_errno, const char *format, va_list ap);
-extern void sptps_log_stderr(sptps_t *s, int s_errno, const char *format, va_list ap);
-extern void (*sptps_log)(sptps_t *s, int s_errno, const char *format, va_list ap);
+extern void sptps_log_quiet(sptps_t *s, int s_errno, const char *format, va_list ap) ATTR_FORMAT(printf, 3, 0);
+extern void sptps_log_stderr(sptps_t *s, int s_errno, const char *format, va_list ap) ATTR_FORMAT(printf, 3, 0);
+extern void (*sptps_log)(sptps_t *s, int s_errno, const char *format, va_list ap) ATTR_FORMAT(printf, 3, 0);