4477 DTrace should speak JSON
Reviewed by: Bryan Cantrill <bmc@joyent.com>

@@ -36,10 +36,14 @@
 
 /*
  * This header file contains a collection of macros that the strtou?ll?
  * functions in common/util use to test characters.  What we need is a kernel
  * version of ctype.h.
+ *
+ * NOTE: These macros are used within several DTrace probe context functions.
+ * They must not be altered to make function calls or perform actions not
+ * safe in probe context.
  */
 
 #if     defined(_KERNEL) && !defined(_BOOT)
 
 #define isalnum(ch)     (isalpha(ch) || isdigit(ch))