Bug 1031168 - Trace the source strings in SavedStacks::PCLocationMap. r=terrence

js/src/gc/Barrier.h

@@ -800,6 +800,7 @@ struct TypeObjectAddendum;
 typedef PreBarriered<JSObject*> PreBarrieredObject;
 typedef PreBarriered<JSScript*> PreBarrieredScript;
 typedef PreBarriered<jit::JitCode*> PreBarrieredJitCode;
+typedef PreBarriered<JSAtom*> PreBarrieredAtom;
 
 typedef RelocatablePtr<JSObject*> RelocatablePtrObject;
 typedef RelocatablePtr<JSScript*> RelocatablePtrScript;

js/src/jit-test/tests/saved-stacks/bug-1031168-trace-sources.js

@@ -0,0 +1,9 @@
+loadFile("\
+saveStack();\
+gcPreserveCode = function() {};\
+gc();\
+saveStack() == 3\
+");
+function loadFile(lfVarx) {
+   evaluate(lfVarx);
+}

js/src/jscompartment.cpp

@@ -556,8 +556,7 @@ JSCompartment::markCrossCompartmentWrappers(JSTracer *trc)
 void
 JSCompartment::trace(JSTracer *trc)
 {
-    // At the moment, this is merely ceremonial, but any live-compartment-only tracing should go
-    // here.
+    savedStacks_.trace(trc);
 }
 
 void

js/src/vm/SavedStacks.cpp

@@ -12,6 +12,7 @@
 #include "jsfriendapi.h"
 #include "jsnum.h"
 
+#include "gc/Marking.h"
 #include "vm/GlobalObject.h"
 #include "vm/StringBuffer.h"
 
@@ -442,6 +443,19 @@ SavedStacks::sweep(JSRuntime *rt)
     }
 }
 
+void
+SavedStacks::trace(JSTracer *trc)
+{
+    if (!pcLocationMap.initialized())
+        return;
+
+    // Mark each of the source strings in our pc to location cache.
+    for (PCLocationMap::Enum e(pcLocationMap); !e.empty(); e.popFront()) {
+        LocationValue &loc = e.front().value();
+        MarkString(trc, &loc.source, "SavedStacks::PCLocationMap's memoized script source name");
+    }
+}
+
 uint32_t
 SavedStacks::count()
 {
@@ -486,14 +500,14 @@ SavedStacks::insertFrames(JSContext *cx, ScriptFrameIter &iter, MutableHandleSav
     if (!insertFrames(cx, ++iter, &parentFrame))
         return false;
 
-    LocationValue location;
+    AutoLocationValueRooter location(cx);
     if (!getLocation(cx, script, pc, &location))
         return false;
 
     SavedFrame::AutoLookupRooter lookup(cx,
-                                        location.source,
-                                        location.line,
-                                        location.column,
+                                        location.get().source,
+                                        location.get().line,
+                                        location.get().column,
                                         callee ? callee->displayAtom() : nullptr,
                                         parentFrame,
                                         compartment->principals);
@@ -589,7 +603,7 @@ SavedStacks::sweepPCLocationMap()
 
 bool
 SavedStacks::getLocation(JSContext *cx, JSScript *script, jsbytecode *pc,
-                         LocationValue *locationp)
+                         MutableHandleLocationValue locationp)
 {
     PCKey key(script, pc);
     PCLocationMap::AddPtr p = pcLocationMap.lookupForAdd(key);
@@ -608,7 +622,7 @@ SavedStacks::getLocation(JSContext *cx, JSScript *script, jsbytecode *pc,
             return false;
     }
 
-    *locationp = p->value();
+    locationp.set(p->value());
     return true;
 }
 

js/src/vm/SavedStacks.h

@@ -106,6 +106,7 @@ class SavedStacks {
     bool     initialized() const { return frames.initialized(); }
     bool     saveCurrentStack(JSContext *cx, MutableHandleSavedFrame frame);
     void     sweep(JSRuntime *rt);
+    void     trace(JSTracer *trc);
     uint32_t count();
     void     clear();
 
@@ -139,9 +140,47 @@ class SavedStacks {
               column(column)
         { }
 
-        ReadBarrieredAtom source;
-        size_t            line;
-        size_t            column;
+        PreBarrieredAtom source;
+        size_t           line;
+        size_t           column;
+    };
+
+    class MOZ_STACK_CLASS AutoLocationValueRooter : public JS::CustomAutoRooter
+    {
+      public:
+        AutoLocationValueRooter(JSContext *cx)
+            : JS::CustomAutoRooter(cx),
+              value() {}
+
+        void set(LocationValue &loc) {
+            value = loc;
+        }
+
+        LocationValue &get() {
+            return value;
+        }
+
+      private:
+        virtual void trace(JSTracer *trc) {
+            if (value.source)
+                gc::MarkString(trc, &value.source, "SavedStacks::LocationValue::source");
+        }
+
+        SavedStacks::LocationValue value;
+    };
+
+    class MOZ_STACK_CLASS MutableHandleLocationValue
+    {
+      public:
+        inline MOZ_IMPLICIT MutableHandleLocationValue(AutoLocationValueRooter *location)
+            : location(location) {}
+
+        void set(LocationValue &loc) {
+            location->set(loc);
+        }
+
+      private:
+        AutoLocationValueRooter *location;
     };
 
     struct PCLocationHasher : public DefaultHasher<PCKey> {
@@ -163,7 +202,8 @@ class SavedStacks {
     PCLocationMap pcLocationMap;
 
     void sweepPCLocationMap();
-    bool getLocation(JSContext *cx, JSScript *script, jsbytecode *pc, LocationValue *locationp);
+    bool getLocation(JSContext *cx, JSScript *script, jsbytecode *pc,
+                     MutableHandleLocationValue locationp);
 };
 
 bool SavedStacksMetadataCallback(JSContext *cx, JSObject **pmetadata);