TritonDataCenter#32: WIP

Make changes according to dap's code review:
  - Do not warn if JSTypedArray type is missing.
  - Clarify/added comments.
  - Formatting/indentation nits.
  - Print <Typed array of length N> when ::jsprinting a typed array.
  - get_map_constructor fails if V8_OFF_MAP_CONSTRUCTOR is missing.
  - Update tests accordingly.

Also, use a separate V8_OFF_MAP_CONSTRUCTOR_OR_BACKPOINTER constant to
store the constructor_or_backpointer offset, and set
V8_OFF_MAP_CONSTRUCTOR with that value if V8_OFF_MAP_CONSTRUCTOR is -1.
Before that change, the same variable was used for both offsets, and
for node versions < 4.x, it would result in V8_OFF_MAP_CONSTRUCTOR
always being -1, which would break, among other things,
get_map_constructor and thus ::findjsobjects.

src/mdb_v8.c

@@ -196,6 +196,7 @@ ssize_t V8_OFF_JSFUNCTION_SHARED;
 ssize_t V8_OFF_JSOBJECT_ELEMENTS;
 ssize_t V8_OFF_JSOBJECT_PROPERTIES;
 ssize_t V8_OFF_MAP_CONSTRUCTOR;
+ssize_t V8_OFF_MAP_CONSTRUCTOR_OR_BACKPOINTER;
 ssize_t V8_OFF_MAP_INOBJECT_PROPERTIES;
 ssize_t V8_OFF_MAP_INSTANCE_ATTRIBUTES;
 ssize_t V8_OFF_MAP_INSTANCE_DESCRIPTORS;
@@ -419,7 +420,7 @@ static v8_offset_t v8_offsets[] = {
 	{ &V8_OFF_MAP_CONSTRUCTOR,
 	    "Map", "constructor",
 	    B_FALSE, V8_CONSTANT_REMOVED_SINCE(4, 3)},
-	{ &V8_OFF_MAP_CONSTRUCTOR,
+	{ &V8_OFF_MAP_CONSTRUCTOR_OR_BACKPOINTER,
 	    "Map", "constructor_or_backpointer",
 	    B_FALSE, V8_CONSTANT_ADDED_SINCE(4, 3)},
 	{ &V8_OFF_MAP_INOBJECT_PROPERTIES,
@@ -721,11 +722,6 @@ autoconfigure(v8_cfg_t *cfgp)
 		failed++;
 	}
 
-	if (V8_TYPE_JSTYPEDARRAY == -1) {
-		mdb_warn("couldn't find JSTypedArray type\n");
-		failed++;
-	}
-
 	/*
 	 * It's non-fatal if we can't find HeapNumber, JSDate, JSRegExp, or
 	 * Oddball because they're only used for heuristics.  It's not even a
@@ -863,6 +859,18 @@ autoconfigure(v8_cfg_t *cfgp)
 		}
 	}
 
+	/*
+	 * With V8 version 4.3, a new "constructor_or_backpointer" field
+	 * replaces the original "constructor" field. Both of them can't
+	 * exist at the same time, and the data they point have similar
+	 * semantics (at least similar enough so that the current code can
+	 * handle either of them transparently). So if the new field exists,
+	 * copy its value into the variable used to hold the old field to
+	 * allow the code to be more concise.
+	 */
+	if (V8_OFF_MAP_CONSTRUCTOR_OR_BACKPOINTER != -1)
+		V8_OFF_MAP_CONSTRUCTOR = V8_OFF_MAP_CONSTRUCTOR_OR_BACKPOINTER;
+
 	return (failed ? -1 : 0);
 }
 
@@ -1552,7 +1560,7 @@ read_heap_dict(uintptr_t addr,
 }
 
 /*
- * Given a JavaScript object's Map "map", stores its constructor
+ * Given a JavaScript object's Map "map", stores the object's constructor
  * in valp. Returns 0 if it succeeded, -1 otherwise.
  */
 static int
@@ -1561,6 +1569,9 @@ get_map_constructor(uintptr_t *valp, uintptr_t map) {
 	int constructor_found = 0;
 	uint8_t type;
 
+	if (V8_OFF_MAP_CONSTRUCTOR == -1)
+		return (-1);
+
 	/*
 	 * https://codereview.chromium.org/950283002, which landed in V8 4.3.x,
 	 * makes the "constructor" and "backpointer to transitions" field
@@ -1571,7 +1582,7 @@ get_map_constructor(uintptr_t *valp, uintptr_t map) {
 	 */
 	while (constructor_found == 0) {
 		if (read_heap_ptr(&constructor_candidate,
-			map, V8_OFF_MAP_CONSTRUCTOR) != 0)
+		    map, V8_OFF_MAP_CONSTRUCTOR) != 0)
 			return (-1);
 
 		if (read_typebyte(&type, constructor_candidate) != 0)
@@ -3448,7 +3459,6 @@ jsobj_print_jstyped_array(uintptr_t addr, jsobj_print_t *jsop)
 {
 	char **bufp = jsop->jsop_bufp;
 	size_t *lenp = jsop->jsop_lenp;
-	int indent = jsop->jsop_indent;
 	uintptr_t length;
 
 	if (V8_OFF_JSTYPEDARRAY_LENGTH == -1 ||
@@ -3458,41 +3468,8 @@ jsobj_print_jstyped_array(uintptr_t addr, jsobj_print_t *jsop)
 		return (-1);
 	}
 
-	if (jsop->jsop_member != NULL) {
-		if (strcmp(jsop->jsop_member, "length") == 0) {
-
-			if (jsop->jsop_baseaddr != NULL)
-				(void) bsnprintf(bufp, lenp, "%p: ",
-				    jsop->jsop_baseaddr);
-
-			(void) bsnprintf(bufp, lenp, "%d", (int)length);
-			jsop->jsop_found = B_TRUE;
-			jsop->jsop_member = NULL;
-			return (0);
-		}
-
-		return (jsobj_properties(addr, jsobj_print_prop_member,
-		    jsop, &jsop->jsop_propinfo));
-	}
-
-	(void) bsnprintf(bufp, lenp, "{\n");
-	(void) bsnprintf(bufp, lenp, "%*s", indent + 4, "");
-
-	(void) bsnprintf(bufp, lenp, "\"length\": ");
-
-	if (jsop->jsop_baseaddr != NULL && jsop->jsop_member == NULL)
-		(void) bsnprintf(bufp, lenp, "%p: ", jsop->jsop_baseaddr);
-
-	(void) bsnprintf(bufp, lenp, "%d,", (int)length);
-
-	++jsop->jsop_nprops;
-
-	jsobj_properties(addr, jsobj_print_prop,
-	    jsop, &jsop->jsop_propinfo);
-	(void) bsnprintf(bufp, lenp, "\n");
-
-	(void) bsnprintf(bufp, lenp, "%*s", indent, "");
-	(void) bsnprintf(bufp, lenp, "}");
+	(void) bsnprintf(bufp, lenp, "<Typed array of length ");
+	(void) bsnprintf(bufp, lenp, "%d>", (int)length);
 
 	return (0);
 }

test/standalone/tst.postmortem_details.js

@@ -189,9 +189,19 @@ gcore.on('exit', function (code) {
 	var mod = util.format('::load %s\n', common.dmodpath());
 	mdb.stdin.write(mod);
 	mdb.stdin.write('!echo test: jsconstructor\n');
-	mdb.stdin.write('::findjsobjects -p my_buffer | ::findjsobjects | ' +
-	    '::jsprint -b length ! awk -F: \'$2 == ' + bufstr.length +
+	// Starting from node v4.0, buffers are actually Uint8Array instances,
+	// and they don't have a "length" property
+	if (process.versions.node < '4.0') {
+		mdb.stdin.write('::findjsobjects -p my_buffer | ' +
+		'::findjsobjects | ' + '::jsprint -b length ! ' +
+		'awk -F: \'$2 == ' + bufstr.length +
 	    '{ print $1 }\'' + '| head -1 > ' + tmpfile + '\n');
+	} else {
+		mdb.stdin.write('::findjsobjects -p my_buffer | ' +
+		'::findjsobjects | ' + '::jsprint -b ! ' +
+	    'awk -F: \'index($2, "length ' + bufstr.length + '>") > 0 ' +
+	    '{ print $1 }\'' + '| head -1 > ' + tmpfile + '\n');
+	}
 	mdb.stdin.write('::cat ' + tmpfile + ' | ::jsconstructor\n');
 	mdb.stdin.write('!echo test: nodebuffer\n');
 	mdb.stdin.write('::cat ' + tmpfile + ' | ::nodebuffer\n');