--- a/usr/src/tools/ctf/cvt/dwarf.c	Sat Jun 30 13:00:47 2012 -0700
+++ b/usr/src/tools/ctf/cvt/dwarf.c	Thu Jun 28 19:37:15 2012 +0100
@@ -22,6 +22,10 @@
  * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
  * Use is subject to license terms.
  */
+/*
+ * Copyright 2012 Jason King.  All rights reserved.
+ * Use is subject to license terms.
+ */
 
 /*
  * DWARF to tdata conversion
@@ -360,6 +364,37 @@
 	return (0);
 }
 
+/*
+ * the following functions lookup the value of an attribute in a DIE:
+ *
+ * die_signed
+ * die_unsigned
+ * die_bool
+ * die_string
+ *
+ * They all take the same parameters (with the exception of valp which is
+ * a pointer to the type of the attribute we are looking up):
+ *
+ * dw - the dwarf object to look in
+ * die - the DIE we're interested in
+ * name - the name of the attribute to lookup
+ * valp - pointer to where the value of the attribute is placed
+ * req - if the value is required (0 / non-zero)
+ *
+ * If the attribute is not found, one of the following happens:
+ * - program terminates (req is non-zero)
+ * - function returns 0
+ *
+ * If the value is found, and in a form (class) we can handle, the function
+ * returns 1.
+ *
+ * Currently, we can only handle attribute values that are stored as
+ * constants (immediate value).  If an attribute has a form we cannot
+ * handle (for example VLAs may store the dimensions of the array
+ * as a DWARF expression that can compute it at runtime by reading
+ * values off the stack or other locations in memory), it is treated
+ * the same as if the attribute does not exist.
+ */
 static int
 die_signed(dwarf_t *dw, Dwarf_Die die, Dwarf_Half name, Dwarf_Signed *valp,
     int req)
@@ -371,6 +406,9 @@
 		return (0); /* die_attr will terminate for us if necessary */
 
 	if (dwarf_formsdata(attr, &val, &dw->dw_err) != DW_DLV_OK) {
+		if (req == 0)
+			return (0);
+
 		terminate("die %llu: failed to get signed (form 0x%x)\n",
 		    die_off(dw, die), die_attr_form(dw, attr));
 	}
@@ -392,6 +430,9 @@
 		return (0); /* die_attr will terminate for us if necessary */
 
 	if (dwarf_formudata(attr, &val, &dw->dw_err) != DW_DLV_OK) {
+		if (req == 0)
+			return (0);
+
 		terminate("die %llu: failed to get unsigned (form 0x%x)\n",
 		    die_off(dw, die), die_attr_form(dw, attr));
 	}
@@ -412,6 +453,9 @@
 		return (0); /* die_attr will terminate for us if necessary */
 
 	if (dwarf_formflag(attr, &val, &dw->dw_err) != DW_DLV_OK) {
+		if (req == 0)
+			return (0);
+
 		terminate("die %llu: failed to get bool (form 0x%x)\n",
 		    die_off(dw, die), die_attr_form(dw, attr));
 	}
@@ -432,6 +476,9 @@
 		return (0); /* die_attr will terminate for us if necessary */
 
 	if (dwarf_formstring(attr, &str, &dw->dw_err) != DW_DLV_OK) {
+		if (req == 0)
+			return (0);
+
 		terminate("die %llu: failed to get string (form 0x%x)\n",
 		    die_off(dw, die), die_attr_form(dw, attr));
 	}