diff -r 000000000000 -r 6474c204b198 js/src/jit/BaselineDebugModeOSR.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit/BaselineDebugModeOSR.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,106 @@
+/* -*- 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 jit_BaselineDebugModeOSR_h
+#define jit_BaselineDebugModeOSR_h
+
+#ifdef JS_ION
+
+#include "jit/BaselineFrame.h"
+#include "jit/BaselineIC.h"
+#include "jit/BaselineJIT.h"
+
+namespace js {
+namespace jit {
+
+// Note that this file and the corresponding .cpp implement debug mode
+// on-stack recompilation. This is to be distinguished from ordinary
+// Baseline->Ion OSR, which is used to jump into compiled loops.
+
+//
+// A volatile location due to recompilation of an on-stack baseline script
+// (e.g., for debug mode toggling).
+//
+// It is usually used in fallback stubs which may trigger on-stack
+// recompilation by calling out into the VM. Example use:
+//
+//     DebugModeOSRVolatileStub<FallbackStubT *> stub(frame, stub_)
+//
+//     // Call out to the VM
+//     // Other effectful operations like TypeScript::Monitor
+//
+//     if (stub.invalid())
+//         return true;
+//
+//     // First use of stub after VM call.
+//
+template <typename T>
+class DebugModeOSRVolatileStub
+{
+    T stub_;
+    BaselineFrame *frame_;
+    uint32_t pcOffset_;
+
+  public:
+    DebugModeOSRVolatileStub(BaselineFrame *frame, ICFallbackStub *stub)
+      : stub_(static_cast<T>(stub)),
+        frame_(frame),
+        pcOffset_(stub->icEntry()->pcOffset())
+    { }
+
+    bool invalid() const {
+        ICEntry &entry = frame_->script()->baselineScript()->icEntryFromPCOffset(pcOffset_);
+        return stub_ != entry.fallbackStub();
+    }
+
+    operator const T&() const { MOZ_ASSERT(!invalid()); return stub_; }
+    T operator->() const { MOZ_ASSERT(!invalid()); return stub_; }
+    T *address() { MOZ_ASSERT(!invalid()); return &stub_; }
+    const T *address() const { MOZ_ASSERT(!invalid()); return &stub_; }
+    T &get() { MOZ_ASSERT(!invalid()); return stub_; }
+    const T &get() const { MOZ_ASSERT(!invalid()); return stub_; }
+
+    bool operator!=(const T &other) const { MOZ_ASSERT(!invalid()); return stub_ != other; }
+    bool operator==(const T &other) const { MOZ_ASSERT(!invalid()); return stub_ == other; }
+};
+
+//
+// Auxiliary info to help the DebugModeOSRHandler fix up state.
+//
+struct BaselineDebugModeOSRInfo
+{
+    uint8_t *resumeAddr;
+    jsbytecode *pc;
+    PCMappingSlotInfo slotInfo;
+    ICEntry::Kind frameKind;
+
+    // Filled in by SyncBaselineDebugModeOSRInfo.
+    uintptr_t stackAdjust;
+    Value valueR0;
+    Value valueR1;
+
+    BaselineDebugModeOSRInfo(jsbytecode *pc, ICEntry::Kind kind)
+      : resumeAddr(nullptr),
+        pc(pc),
+        slotInfo(0),
+        frameKind(kind),
+        stackAdjust(0),
+        valueR0(UndefinedValue()),
+        valueR1(UndefinedValue())
+    { }
+
+    void popValueInto(PCMappingSlotInfo::SlotLocation loc, Value *vp);
+};
+
+bool
+RecompileOnStackBaselineScriptsForDebugMode(JSContext *cx, JSCompartment *comp);
+
+} // namespace jit
+} // namespace js
+
+#endif // JS_ION
+
+#endif // jit_BaselineDebugModeOSR_h