Add m-esr52 at 52.6.0

1 files changed, 332 insertions, 0 deletions

diff --git a/js/src/vm/SavedStacks.h b/js/src/vm/SavedStacks.h
new file mode 100644
index 000000000..57b56081b
--- /dev/null
+++ b/js/src/vm/SavedStacks.h
@@ -0,0 +1,332 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef vm_SavedStacks_h
+#define vm_SavedStacks_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/FastBernoulliTrial.h"
+
+#include "jscntxt.h"
+#include "jsmath.h"
+#include "jswrapper.h"
+#include "js/HashTable.h"
+#include "vm/SavedFrame.h"
+#include "vm/Stack.h"
+
+namespace js {
+
+// # Saved Stacks
+//
+// The `SavedStacks` class provides a compact way to capture and save JS stacks
+// as `SavedFrame` `JSObject` subclasses. A single `SavedFrame` object
+// represents one frame that was on the stack, and has a strong reference to its
+// parent `SavedFrame` (the next youngest frame). This reference is null when
+// the `SavedFrame` object is the oldest frame that was on the stack.
+//
+// This comment documents implementation. For usage documentation, see the
+// `js/src/doc/SavedFrame/SavedFrame.md` file and relevant `SavedFrame`
+// functions in `js/src/jsapi.h`.
+//
+// ## Compact
+//
+// Older saved stack frame tails are shared via hash consing, to deduplicate
+// structurally identical data. `SavedStacks` contains a hash table of weakly
+// held `SavedFrame` objects, and when the owning compartment is swept, it
+// removes entries from this table that aren't held alive in any other way. When
+// saving new stacks, we use this table to find pre-existing `SavedFrame`
+// objects. If such an object is already extant, it is reused; otherwise a new
+// `SavedFrame` is allocated and inserted into the table.
+//
+//    Naive         |   Hash Consing
+//    --------------+------------------
+//    c -> b -> a   |   c -> b -> a
+//                  |        ^
+//    d -> b -> a   |   d ---|
+//                  |        |
+//    e -> b -> a   |   e ---'
+//
+// This technique is effective because of the nature of the events that trigger
+// capturing the stack. Currently, these events consist primarily of `JSObject`
+// allocation (when an observing `Debugger` has such tracking), `Promise`
+// settlement, and `Error` object creation. While these events may occur many
+// times, they tend to occur only at a few locations in the JS source. For
+// example, if we enable Object allocation tracking and run the esprima
+// JavaScript parser on its own JavaScript source, there are approximately 54700
+// total `Object` allocations, but just ~1400 unique JS stacks at allocation
+// time. There's only ~200 allocation sites if we capture only the youngest
+// stack frame.
+//
+// ## Security and Wrappers
+//
+// We save every frame on the stack, regardless of whether the `SavedStack`'s
+// compartment's principals subsume the frame's compartment's principals or
+// not. This gives us maximum flexibility down the line when accessing and
+// presenting captured stacks, but at the price of some complication involved in
+// preventing the leakage of privileged stack frames to unprivileged callers.
+//
+// When a `SavedFrame` method or accessor is called, we compare the caller's
+// compartment's principals to each `SavedFrame`'s captured principals. We avoid
+// using the usual `CallNonGenericMethod` and `nativeCall` machinery which
+// enters the `SavedFrame` object's compartment before we can check these
+// principals, because we need access to the original caller's compartment's
+// principals (unlike other `CallNonGenericMethod` users) to determine what view
+// of the stack to present. Instead, we take a similar approach to that used by
+// DOM methods, and manually unwrap wrappers until we get the underlying
+// `SavedFrame` object, find the first `SavedFrame` in its stack whose captured
+// principals are subsumed by the caller's principals, access the reserved slots
+// we care about, and then rewrap return values as necessary.
+//
+// Consider the following diagram:
+//
+//                                              Content Compartment
+//                                    +---------------------------------------+
+//                                    |                                       |
+//                                    |           +------------------------+  |
+//      Chrome Compartment            |           |                        |  |
+//    +--------------------+          |           | SavedFrame C (content) |  |
+//    |                    |          |           |                        |  |
+//    |                  +--------------+         +------------------------+  |
+//    |                  |              |                    ^                |
+//    |     var x -----> | Xray Wrapper |-----.              |                |
+//    |                  |              |     |              |                |
+//    |                  +--------------+     |   +------------------------+  |
+//    |                    |          |       |   |                        |  |
+//    |                  +--------------+     |   | SavedFrame B (content) |  |
+//    |                  |              |     |   |                        |  |
+//    |     var y -----> | CCW (waived) |--.  |   +------------------------+  |
+//    |                  |              |  |  |              ^                |
+//    |                  +--------------+  |  |              |                |
+//    |                    |          |    |  |              |                |
+//    +--------------------+          |    |  |   +------------------------+  |
+//                                    |    |  '-> |                        |  |
+//                                    |    |      | SavedFrame A (chrome)  |  |
+//                                    |    '----> |                        |  |
+//                                    |           +------------------------+  |
+//                                    |                      ^                |
+//                                    |                      |                |
+//                                    |           var z -----'                |
+//                                    |                                       |
+//                                    +---------------------------------------+
+//
+// CCW is a plain cross-compartment wrapper, yielded by waiving Xray vision. A
+// is the youngest `SavedFrame` and represents a frame that was from the chrome
+// compartment, while B and C are from frames from the content compartment. C is
+// the oldest frame.
+//
+// Note that it is always safe to waive an Xray around a SavedFrame object,
+// because SavedFrame objects and the SavedFrame prototype are always frozen you
+// will never run untrusted code.
+//
+// Depending on who the caller is, the view of the stack will be different, and
+// is summarized in the table below.
+//
+//    Var  | View
+//    -----+------------
+//    x    | A -> B -> C
+//    y, z | B -> C
+//
+// In the case of x, the `SavedFrame` accessors are called with an Xray wrapper
+// around the `SavedFrame` object as the `this` value, and the chrome
+// compartment as the cx's current principals. Because the chrome compartment's
+// principals subsume both itself and the content compartment's principals, x
+// has the complete view of the stack.
+//
+// In the case of y, the cross-compartment machinery automatically enters the
+// content compartment, and calls the `SavedFrame` accessors with the wrapped
+// `SavedFrame` object as the `this` value. Because the cx's current compartment
+// is the content compartment, and the content compartment's principals do not
+// subsume the chrome compartment's principals, it can only see the B and C
+// frames.
+//
+// In the case of z, the `SavedFrame` accessors are called with the `SavedFrame`
+// object in the `this` value, and the content compartment as the cx's current
+// compartment. Similar to the case of y, only the B and C frames are exposed
+// because the cx's current compartment's principals do not subsume A's captured
+// principals.
+
+class SavedStacks {
+    friend class SavedFrame;
+    friend bool JS::ubi::ConstructSavedFrameStackSlow(JSContext* cx,
+                                                      JS::ubi::StackFrame& ubiFrame,
+                                                      MutableHandleObject outSavedFrameStack);
+
+  public:
+    SavedStacks()
+      : frames(),
+        bernoulliSeeded(false),
+        bernoulli(1.0, 0x59fdad7f6b4cc573, 0x91adf38db96a9354),
+        creatingSavedFrame(false)
+    { }
+
+    MOZ_MUST_USE bool init();
+    bool initialized() const { return frames.initialized(); }
+    MOZ_MUST_USE bool saveCurrentStack(JSContext* cx, MutableHandleSavedFrame frame,
+                                       JS::StackCapture&& capture = JS::StackCapture(JS::AllFrames()));
+    MOZ_MUST_USE bool copyAsyncStack(JSContext* cx, HandleObject asyncStack,
+                                     HandleString asyncCause,
+                                     MutableHandleSavedFrame adoptedStack,
+                                     uint32_t maxFrameCount = 0);
+    void sweep();
+    void trace(JSTracer* trc);
+    uint32_t count();
+    void clear();
+    void chooseSamplingProbability(JSCompartment*);
+
+    // Set the sampling random number generator's state to |state0| and
+    // |state1|. One or the other must be non-zero. See the comments for
+    // mozilla::non_crypto::XorShift128PlusRNG::setState for details.
+    void setRNGState(uint64_t state0, uint64_t state1) { bernoulli.setRandomState(state0, state1); }
+
+    size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf);
+
+    // An alloction metadata builder that marks cells with the JavaScript stack
+    // at which they were allocated.
+    struct MetadataBuilder : public AllocationMetadataBuilder {
+        MetadataBuilder() : AllocationMetadataBuilder() { }
+        virtual JSObject* build(JSContext *cx, HandleObject obj,
+                                AutoEnterOOMUnsafeRegion& oomUnsafe) const override;
+    };
+
+    static const MetadataBuilder metadataBuilder;
+
+  private:
+    SavedFrame::Set frames;
+    bool bernoulliSeeded;
+    mozilla::FastBernoulliTrial bernoulli;
+    bool creatingSavedFrame;
+
+    // Similar to mozilla::ReentrancyGuard, but instead of asserting against
+    // reentrancy, just change the behavior of SavedStacks::saveCurrentStack to
+    // return a nullptr SavedFrame.
+    struct MOZ_RAII AutoReentrancyGuard {
+        MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER;
+        SavedStacks& stacks;
+
+        explicit AutoReentrancyGuard(SavedStacks& stacks MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+            : stacks(stacks)
+        {
+            MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+            stacks.creatingSavedFrame = true;
+        }
+
+        ~AutoReentrancyGuard()
+        {
+            stacks.creatingSavedFrame = false;
+        }
+    };
+
+    MOZ_MUST_USE bool insertFrames(JSContext* cx, FrameIter& iter,
+                                   MutableHandleSavedFrame frame,
+                                   JS::StackCapture&& capture);
+    MOZ_MUST_USE bool adoptAsyncStack(JSContext* cx, HandleSavedFrame asyncStack,
+                                      HandleString asyncCause,
+                                      MutableHandleSavedFrame adoptedStack,
+                                      uint32_t maxFrameCount);
+    SavedFrame* getOrCreateSavedFrame(JSContext* cx, SavedFrame::HandleLookup lookup);
+    SavedFrame* createFrameFromLookup(JSContext* cx, SavedFrame::HandleLookup lookup);
+
+    // Cache for memoizing PCToLineNumber lookups.
+
+    struct PCKey {
+        PCKey(JSScript* script, jsbytecode* pc) : script(script), pc(pc) { }
+
+        HeapPtr<JSScript*> script;
+        jsbytecode* pc;
+
+        void trace(JSTracer* trc) { /* PCKey is weak. */ }
+        bool needsSweep() { return IsAboutToBeFinalized(&script); }
+    };
+
+  public:
+    struct LocationValue {
+        LocationValue() : source(nullptr), line(0), column(0) { }
+        LocationValue(JSAtom* source, size_t line, uint32_t column)
+            : source(source), line(line), column(column)
+        { }
+
+        void trace(JSTracer* trc) {
+            TraceNullableEdge(trc, &source, "SavedStacks::LocationValue::source");
+        }
+
+        bool needsSweep() {
+            // LocationValue is always held strongly, but in a weak map.
+            // Assert that it has been marked already, but allow it to be
+            // ejected from the map when the key dies.
+            MOZ_ASSERT(source);
+            MOZ_ASSERT(!IsAboutToBeFinalized(&source));
+            return true;
+        }
+
+        HeapPtr<JSAtom*> source;
+        size_t line;
+        uint32_t column;
+    };
+
+    template <typename Outer>
+    struct LocationValueOperations {
+        JSAtom* source() const { return loc().source; }
+        size_t line() const { return loc().line; }
+        uint32_t column() const { return loc().column; }
+      private:
+        const LocationValue& loc() const { return static_cast<const Outer*>(this)->get(); }
+    };
+
+    template <typename Outer>
+    struct MutableLocationValueOperations : public LocationValueOperations<Outer> {
+        void setSource(JSAtom* v) { loc().source = v; }
+        void setLine(size_t v) { loc().line = v; }
+        void setColumn(uint32_t v) { loc().column = v; }
+      private:
+        LocationValue& loc() { return static_cast<Outer*>(this)->get(); }
+    };
+
+  private:
+    struct PCLocationHasher : public DefaultHasher<PCKey> {
+        using ScriptPtrHasher = DefaultHasher<JSScript*>;
+        using BytecodePtrHasher = DefaultHasher<jsbytecode*>;
+
+        static HashNumber hash(const PCKey& key) {
+            return mozilla::AddToHash(ScriptPtrHasher::hash(key.script),
+                                      BytecodePtrHasher::hash(key.pc));
+        }
+
+        static bool match(const PCKey& l, const PCKey& k) {
+            return ScriptPtrHasher::match(l.script, k.script) &&
+                   BytecodePtrHasher::match(l.pc, k.pc);
+        }
+    };
+
+    // We eagerly Atomize the script source stored in LocationValue because
+    // wasm does not always have a JSScript and the source might not be
+    // available when we need it later. However, since the JSScript does not
+    // actually hold this atom, we have to trace it strongly to keep it alive.
+    // Thus, it takes two GC passes to fully clean up this table: the first GC
+    // removes the dead script; the second will clear out the source atom since
+    // it is no longer held by the table.
+    using PCLocationMap = GCHashMap<PCKey, LocationValue, PCLocationHasher, SystemAllocPolicy>;
+    PCLocationMap pcLocationMap;
+
+    MOZ_MUST_USE bool getLocation(JSContext* cx, const FrameIter& iter,
+                                  MutableHandle<LocationValue> locationp);
+};
+
+template <>
+class RootedBase<SavedStacks::LocationValue>
+  : public SavedStacks::MutableLocationValueOperations<JS::Rooted<SavedStacks::LocationValue>>
+{};
+
+template <>
+class MutableHandleBase<SavedStacks::LocationValue>
+  : public SavedStacks::MutableLocationValueOperations<JS::MutableHandle<SavedStacks::LocationValue>>
+{};
+
+UTF8CharsZ
+BuildUTF8StackString(JSContext* cx, HandleObject stack);
+
+} /* namespace js */
+
+#endif /* vm_SavedStacks_h */