Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 808 insertions, 0 deletions

diff --git a/js/src/jit/JitcodeMap.h b/js/src/jit/JitcodeMap.h
new file mode 100644
index 0000000000..b4ed8ae7ff
--- /dev/null
+++ b/js/src/jit/JitcodeMap.h
@@ -0,0 +1,808 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * 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_JitcodeMap_h
+#define jit_JitcodeMap_h
+
+#include "mozilla/Assertions.h"  // MOZ_ASSERT, MOZ_ASSERT_IF, MOZ_CRASH
+
+#include <stddef.h>  // size_t
+#include <stdint.h>  // uint8_t, uint32_t, uint64_t
+
+#include "ds/AvlTree.h"         // AvlTree
+#include "jit/CompactBuffer.h"  // CompactBufferReader, CompactBufferWriter
+#include "jit/shared/Assembler-shared.h"  // CodeOffset
+#include "js/AllocPolicy.h"               // SystemAllocPolicy
+#include "js/TypeDecls.h"                 // jsbytecode
+#include "js/Vector.h"                    // Vector
+#include "vm/BytecodeLocation.h"          // BytecodeLocation
+
+class JSScript;
+class JSTracer;
+struct JSRuntime;
+
+namespace JS {
+class Zone;
+}  // namespace JS
+
+namespace js {
+
+class GCMarker;
+
+namespace jit {
+
+class InlineScriptTree;
+
+/*
+ * The jitcode map implements tables to allow mapping from addresses in jitcode
+ * to the list of (JSScript*, jsbytecode*) pairs that are implicitly active in
+ * the frame at that point in the native code.
+ *
+ * To represent this information efficiently, a multi-level table is used.
+ *
+ * At the top level, a global AVL-tree of JitcodeGlobalEntry describing the
+ * mapping for each individual JitCode generated by compiles.  The entries are
+ * ordered by their nativeStartAddr.
+ *
+ * Every entry in the table is of fixed size, but there are different entry
+ * types, distinguished by the kind field.
+ */
+
+class JitcodeGlobalTable;
+class JitcodeIonTable;
+class JitcodeRegionEntry;
+
+struct NativeToBytecode {
+  CodeOffset nativeOffset;
+  InlineScriptTree* tree;
+  jsbytecode* pc;
+};
+
+// Describes range [start, end) of JIT-generated code.
+class JitCodeRange {
+ protected:
+  void* const nativeStartAddr_;
+  void* const nativeEndAddr_;
+
+ public:
+  JitCodeRange(void* start, void* end)
+      : nativeStartAddr_(start), nativeEndAddr_(end) {
+    MOZ_ASSERT(start < end);
+  }
+
+  // Comparator used by the AvlTree.
+  static int compare(const JitCodeRange* r1, const JitCodeRange* r2) {
+    // JitCodeRange includes 'start' but excludes 'end'.
+    if (r1->nativeEndAddr_ <= r2->nativeStartAddr_) {
+      return -1;
+    }
+    if (r1->nativeStartAddr_ >= r2->nativeEndAddr_) {
+      return 1;
+    }
+    return 0;
+  }
+
+  void* nativeStartAddr() const { return nativeStartAddr_; }
+  void* nativeEndAddr() const { return nativeEndAddr_; }
+
+  bool containsPointer(void* ptr) const {
+    return nativeStartAddr() <= ptr && ptr < nativeEndAddr();
+  }
+};
+
+typedef Vector<BytecodeLocation, 0, SystemAllocPolicy> BytecodeLocationVector;
+
+class IonEntry;
+class IonICEntry;
+class BaselineEntry;
+class BaselineInterpreterEntry;
+class DummyEntry;
+
+// Base class for all entries.
+class JitcodeGlobalEntry : public JitCodeRange {
+ protected:
+  JitCode* jitcode_;
+  // If this entry is referenced from the profiler buffer, this is the
+  // position where the most recent sample that references it starts.
+  // Otherwise set to kNoSampleInBuffer.
+  static const uint64_t kNoSampleInBuffer = UINT64_MAX;
+  uint64_t samplePositionInBuffer_ = kNoSampleInBuffer;
+
+ public:
+  enum class Kind : uint8_t {
+    Ion,
+    IonIC,
+    Baseline,
+    BaselineInterpreter,
+    Dummy
+  };
+
+ protected:
+  Kind kind_;
+
+  JitcodeGlobalEntry(Kind kind, JitCode* code, void* nativeStartAddr,
+                     void* nativeEndAddr)
+      : JitCodeRange(nativeStartAddr, nativeEndAddr),
+        jitcode_(code),
+        kind_(kind) {
+    MOZ_ASSERT(code);
+    MOZ_ASSERT(nativeStartAddr);
+    MOZ_ASSERT(nativeEndAddr);
+  }
+
+  // Protected destructor to ensure this is called through DestroyPolicy.
+  ~JitcodeGlobalEntry() = default;
+
+  JitcodeGlobalEntry(const JitcodeGlobalEntry& other) = delete;
+  void operator=(const JitcodeGlobalEntry& other) = delete;
+
+ public:
+  struct DestroyPolicy {
+    void operator()(JitcodeGlobalEntry* entry);
+  };
+
+  void setSamplePositionInBuffer(uint64_t bufferWritePos) {
+    samplePositionInBuffer_ = bufferWritePos;
+  }
+  void setAsExpired() { samplePositionInBuffer_ = kNoSampleInBuffer; }
+  bool isSampled(uint64_t bufferRangeStart) {
+    if (samplePositionInBuffer_ == kNoSampleInBuffer) {
+      return false;
+    }
+    return bufferRangeStart <= samplePositionInBuffer_;
+  }
+
+  Kind kind() const { return kind_; }
+  bool isIon() const { return kind() == Kind::Ion; }
+  bool isIonIC() const { return kind() == Kind::IonIC; }
+  bool isBaseline() const { return kind() == Kind::Baseline; }
+  bool isBaselineInterpreter() const {
+    return kind() == Kind::BaselineInterpreter;
+  }
+  bool isDummy() const { return kind() == Kind::Dummy; }
+
+  inline const IonEntry& asIon() const;
+  inline const IonICEntry& asIonIC() const;
+  inline const BaselineEntry& asBaseline() const;
+  inline const BaselineInterpreterEntry& asBaselineInterpreter() const;
+  inline const DummyEntry& asDummy() const;
+
+  inline IonEntry& asIon();
+  inline IonICEntry& asIonIC();
+  inline BaselineEntry& asBaseline();
+  inline BaselineInterpreterEntry& asBaselineInterpreter();
+  inline DummyEntry& asDummy();
+
+  JitCode* jitcode() const { return jitcode_; }
+  JitCode** jitcodePtr() { return &jitcode_; }
+  Zone* zone() const { return jitcode()->zone(); }
+
+  bool traceJitcode(JSTracer* trc);
+  bool isJitcodeMarkedFromAnyThread(JSRuntime* rt);
+
+  bool trace(JSTracer* trc);
+  void traceWeak(JSTracer* trc);
+  uint64_t lookupRealmID(JSRuntime* rt, void* ptr) const;
+  void* canonicalNativeAddrFor(JSRuntime* rt, void* ptr) const;
+
+  // Read the inline call stack at a given point in the native code and append
+  // into the given vector.  Innermost (script,pc) pair will be appended first,
+  // and outermost appended last.
+  //
+  // Returns false on memory failure.
+  [[nodiscard]] bool callStackAtAddr(JSRuntime* rt, void* ptr,
+                                     BytecodeLocationVector& results,
+                                     uint32_t* depth) const;
+  uint32_t callStackAtAddr(JSRuntime* rt, void* ptr, const char** results,
+                           uint32_t maxResults) const;
+};
+
+using UniqueJitcodeGlobalEntry =
+    UniquePtr<JitcodeGlobalEntry, JitcodeGlobalEntry::DestroyPolicy>;
+
+template <typename T, typename... Args>
+inline UniqueJitcodeGlobalEntry MakeJitcodeGlobalEntry(JSContext* cx,
+                                                       Args&&... args) {
+  UniqueJitcodeGlobalEntry res(js_new<T>(std::forward<Args>(args)...));
+  if (!res) {
+    ReportOutOfMemory(cx);
+  }
+  return res;
+}
+
+class IonEntry : public JitcodeGlobalEntry {
+ public:
+  struct ScriptNamePair {
+    JSScript* script;
+    UniqueChars str;
+    ScriptNamePair(JSScript* script, UniqueChars str)
+        : script(script), str(std::move(str)) {}
+  };
+  using ScriptList = Vector<ScriptNamePair, 2, SystemAllocPolicy>;
+
+ private:
+  ScriptList scriptList_;
+
+  // regionTable_ points to the start of the region table within the
+  // packed map for compile represented by this entry.  Since the
+  // region table occurs at the tail of the memory region, this pointer
+  // points somewhere inside the region memory space, and not to the start
+  // of the memory space.
+  const JitcodeIonTable* regionTable_;
+
+ public:
+  IonEntry(JitCode* code, void* nativeStartAddr, void* nativeEndAddr,
+           ScriptList&& scriptList, JitcodeIonTable* regionTable)
+      : JitcodeGlobalEntry(Kind::Ion, code, nativeStartAddr, nativeEndAddr),
+        scriptList_(std::move(scriptList)),
+        regionTable_(regionTable) {
+    MOZ_ASSERT(regionTable);
+  }
+
+  ~IonEntry();
+
+  ScriptList& scriptList() { return scriptList_; }
+
+  size_t numScripts() const { return scriptList_.length(); }
+
+  JSScript* getScript(unsigned idx) const {
+    MOZ_ASSERT(idx < numScripts());
+    return scriptList_[idx].script;
+  }
+
+  const char* getStr(unsigned idx) const {
+    MOZ_ASSERT(idx < numScripts());
+    return scriptList_[idx].str.get();
+  }
+
+  const JitcodeIonTable* regionTable() const { return regionTable_; }
+
+  void* canonicalNativeAddrFor(void* ptr) const;
+
+  [[nodiscard]] bool callStackAtAddr(void* ptr, BytecodeLocationVector& results,
+                                     uint32_t* depth) const;
+
+  uint32_t callStackAtAddr(void* ptr, const char** results,
+                           uint32_t maxResults) const;
+
+  uint64_t lookupRealmID(void* ptr) const;
+
+  bool trace(JSTracer* trc);
+  void traceWeak(JSTracer* trc);
+};
+
+class IonICEntry : public JitcodeGlobalEntry {
+  // Address for this IC in the IonScript code. Most operations on IonICEntry
+  // use this to forward to the IonEntry.
+  void* rejoinAddr_;
+
+ public:
+  IonICEntry(JitCode* code, void* nativeStartAddr, void* nativeEndAddr,
+             void* rejoinAddr)
+      : JitcodeGlobalEntry(Kind::IonIC, code, nativeStartAddr, nativeEndAddr),
+        rejoinAddr_(rejoinAddr) {
+    MOZ_ASSERT(rejoinAddr_);
+  }
+
+  void* rejoinAddr() const { return rejoinAddr_; }
+
+  void* canonicalNativeAddrFor(void* ptr) const;
+
+  [[nodiscard]] bool callStackAtAddr(JSRuntime* rt, void* ptr,
+                                     BytecodeLocationVector& results,
+                                     uint32_t* depth) const;
+
+  uint32_t callStackAtAddr(JSRuntime* rt, void* ptr, const char** results,
+                           uint32_t maxResults) const;
+
+  uint64_t lookupRealmID(JSRuntime* rt, void* ptr) const;
+
+  bool trace(JSTracer* trc);
+  void traceWeak(JSTracer* trc);
+};
+
+class BaselineEntry : public JitcodeGlobalEntry {
+  JSScript* script_;
+  UniqueChars str_;
+
+ public:
+  BaselineEntry(JitCode* code, void* nativeStartAddr, void* nativeEndAddr,
+                JSScript* script, UniqueChars str)
+      : JitcodeGlobalEntry(Kind::Baseline, code, nativeStartAddr,
+                           nativeEndAddr),
+        script_(script),
+        str_(std::move(str)) {
+    MOZ_ASSERT(script_);
+    MOZ_ASSERT(str_);
+  }
+
+  JSScript* script() const { return script_; }
+
+  const char* str() const { return str_.get(); }
+
+  void* canonicalNativeAddrFor(void* ptr) const;
+
+  [[nodiscard]] bool callStackAtAddr(void* ptr, BytecodeLocationVector& results,
+                                     uint32_t* depth) const;
+
+  uint32_t callStackAtAddr(void* ptr, const char** results,
+                           uint32_t maxResults) const;
+
+  uint64_t lookupRealmID() const;
+
+  bool trace(JSTracer* trc);
+  void traceWeak(JSTracer* trc);
+};
+
+class BaselineInterpreterEntry : public JitcodeGlobalEntry {
+ public:
+  BaselineInterpreterEntry(JitCode* code, void* nativeStartAddr,
+                           void* nativeEndAddr)
+      : JitcodeGlobalEntry(Kind::BaselineInterpreter, code, nativeStartAddr,
+                           nativeEndAddr) {}
+
+  void* canonicalNativeAddrFor(void* ptr) const;
+
+  [[nodiscard]] bool callStackAtAddr(void* ptr, BytecodeLocationVector& results,
+                                     uint32_t* depth) const;
+
+  uint32_t callStackAtAddr(void* ptr, const char** results,
+                           uint32_t maxResults) const;
+
+  uint64_t lookupRealmID() const;
+};
+
+// Dummy entries are created for jitcode generated when profiling is not
+// turned on, so that they have representation in the global table if they are
+// on the stack when profiling is enabled.
+class DummyEntry : public JitcodeGlobalEntry {
+ public:
+  DummyEntry(JitCode* code, void* nativeStartAddr, void* nativeEndAddr)
+      : JitcodeGlobalEntry(Kind::Dummy, code, nativeStartAddr, nativeEndAddr) {}
+
+  void* canonicalNativeAddrFor(JSRuntime* rt, void* ptr) const {
+    return nullptr;
+  }
+
+  [[nodiscard]] bool callStackAtAddr(JSRuntime* rt, void* ptr,
+                                     BytecodeLocationVector& results,
+                                     uint32_t* depth) const {
+    return true;
+  }
+
+  uint32_t callStackAtAddr(JSRuntime* rt, void* ptr, const char** results,
+                           uint32_t maxResults) const {
+    return 0;
+  }
+
+  uint64_t lookupRealmID() const { return 0; }
+};
+
+inline const IonEntry& JitcodeGlobalEntry::asIon() const {
+  MOZ_ASSERT(isIon());
+  return *static_cast<const IonEntry*>(this);
+}
+
+inline const IonICEntry& JitcodeGlobalEntry::asIonIC() const {
+  MOZ_ASSERT(isIonIC());
+  return *static_cast<const IonICEntry*>(this);
+}
+
+inline const BaselineEntry& JitcodeGlobalEntry::asBaseline() const {
+  MOZ_ASSERT(isBaseline());
+  return *static_cast<const BaselineEntry*>(this);
+}
+
+inline const BaselineInterpreterEntry&
+JitcodeGlobalEntry::asBaselineInterpreter() const {
+  MOZ_ASSERT(isBaselineInterpreter());
+  return *static_cast<const BaselineInterpreterEntry*>(this);
+}
+
+inline const DummyEntry& JitcodeGlobalEntry::asDummy() const {
+  MOZ_ASSERT(isDummy());
+  return *static_cast<const DummyEntry*>(this);
+}
+
+inline IonEntry& JitcodeGlobalEntry::asIon() {
+  MOZ_ASSERT(isIon());
+  return *static_cast<IonEntry*>(this);
+}
+
+inline IonICEntry& JitcodeGlobalEntry::asIonIC() {
+  MOZ_ASSERT(isIonIC());
+  return *static_cast<IonICEntry*>(this);
+}
+
+inline BaselineEntry& JitcodeGlobalEntry::asBaseline() {
+  MOZ_ASSERT(isBaseline());
+  return *static_cast<BaselineEntry*>(this);
+}
+
+inline BaselineInterpreterEntry& JitcodeGlobalEntry::asBaselineInterpreter() {
+  MOZ_ASSERT(isBaselineInterpreter());
+  return *static_cast<BaselineInterpreterEntry*>(this);
+}
+
+inline DummyEntry& JitcodeGlobalEntry::asDummy() {
+  MOZ_ASSERT(isDummy());
+  return *static_cast<DummyEntry*>(this);
+}
+
+// Global table of JitcodeGlobalEntry entries.
+class JitcodeGlobalTable {
+ private:
+  // Vector containing (and owning) all entries. This is unsorted and used for
+  // iterating over all entries, because the AvlTree currently doesn't support
+  // modifications while iterating.
+  using EntryVector = Vector<UniqueJitcodeGlobalEntry, 0, SystemAllocPolicy>;
+  EntryVector entries_;
+
+  // AVL tree containing all entries in the Vector above. This is used to
+  // efficiently look up the entry corresponding to a native code address.
+  using EntryTree = AvlTree<JitCodeRange*, JitCodeRange>;
+  static const size_t LIFO_CHUNK_SIZE = 16 * 1024;
+  LifoAlloc alloc_;
+  EntryTree tree_;
+
+ public:
+  JitcodeGlobalTable() : alloc_(LIFO_CHUNK_SIZE), tree_(&alloc_) {}
+
+  bool empty() const {
+    MOZ_ASSERT(entries_.empty() == tree_.empty());
+    return entries_.empty();
+  }
+
+  JitcodeGlobalEntry* lookup(void* ptr) { return lookupInternal(ptr); }
+
+  const JitcodeGlobalEntry* lookupForSampler(void* ptr, JSRuntime* rt,
+                                             uint64_t samplePosInBuffer);
+
+  [[nodiscard]] bool addEntry(UniqueJitcodeGlobalEntry entry);
+
+  void setAllEntriesAsExpired();
+  [[nodiscard]] bool markIteratively(GCMarker* marker);
+  void traceWeak(JSRuntime* rt, JSTracer* trc);
+
+ private:
+  JitcodeGlobalEntry* lookupInternal(void* ptr);
+};
+
+// clang-format off
+/*
+ * Container class for main jitcode table.
+ * The Region table's memory is structured as follows:
+ *
+ *      +------------------------------------------------+   |
+ *      |  Region 1 Run                                  |   |
+ *      |------------------------------------------------|   |
+ *      |  Region 2 Run                                  |   |
+ *      |                                                |   |
+ *      |                                                |   |
+ *      |------------------------------------------------|   |
+ *      |  Region 3 Run                                  |   |
+ *      |                                                |   |
+ *      |------------------------------------------------|   |-- Payload
+ *      |                                                |   |
+ *      |               ...                              |   |
+ *      |                                                |   |
+ *      |------------------------------------------------|   |
+ *      |  Region M Run                                  |   |
+ *      |                                                |   |
+ *      +================================================+ <- RegionTable pointer points here
+ *      | uint23_t numRegions = M                        |   |
+ *      +------------------------------------------------+   |
+ *      | Region 1                                       |   |
+ *      |   uint32_t entryOffset = size(Payload)         |   |
+ *      +------------------------------------------------+   |
+ *      |                                                |   |-- Table
+ *      |   ...                                          |   |
+ *      |                                                |   |
+ *      +------------------------------------------------+   |
+ *      | Region M                                       |   |
+ *      |   uint32_t entryOffset                         |   |
+ *      +------------------------------------------------+   |
+ *
+ * The region table is composed of two sections: a tail section that contains a table of
+ * fixed-size entries containing offsets into the the head section, and a head section that
+ * holds a sequence of variable-sized runs.  The table in the tail section serves to
+ * locate the variable-length encoded structures in the head section.
+ *
+ * The entryOffsets in the table indicate the bytes offset to subtract from the regionTable
+ * pointer to arrive at the encoded region in the payload.
+ *
+ *
+ * Variable-length entries in payload
+ * ----------------------------------
+ * The entryOffsets in the region table's fixed-sized entries refer to a location within the
+ * variable-length payload section.  This location contains a compactly encoded "run" of
+ * mappings.
+ *
+ * Each run starts by describing the offset within the native code it starts at, and the
+ * sequence of (JSScript*, jsbytecode*) pairs active at that site.  Following that, there
+ * are a number of variable-length entries encoding (nativeOffsetDelta, bytecodeOffsetDelta)
+ * pairs for the run.
+ *
+ *      VarUint32 nativeOffset;
+ *          - The offset from nativeStartAddr in the global table entry at which
+ *            the jitcode for this region starts.
+ *
+ *      Uint8_t scriptDepth;
+ *          - The depth of inlined scripts for this region.
+ *
+ *      List<VarUint32> inlineScriptPcStack;
+ *          - We encode (2 * scriptDepth) VarUint32s here.  Each pair of uint32s are taken
+ *            as an index into the scriptList in the global table entry, and a pcOffset
+ *            respectively.
+ *
+ *      List<NativeAndBytecodeDelta> deltaRun;
+ *          - The rest of the entry is a deltaRun that stores a series of variable-length
+ *            encoded NativeAndBytecodeDelta datums.
+ */
+// clang-format on
+class JitcodeRegionEntry {
+ private:
+  static const unsigned MAX_RUN_LENGTH = 100;
+
+ public:
+  static void WriteHead(CompactBufferWriter& writer, uint32_t nativeOffset,
+                        uint8_t scriptDepth);
+  static void ReadHead(CompactBufferReader& reader, uint32_t* nativeOffset,
+                       uint8_t* scriptDepth);
+
+  static void WriteScriptPc(CompactBufferWriter& writer, uint32_t scriptIdx,
+                            uint32_t pcOffset);
+  static void ReadScriptPc(CompactBufferReader& reader, uint32_t* scriptIdx,
+                           uint32_t* pcOffset);
+
+  static void WriteDelta(CompactBufferWriter& writer, uint32_t nativeDelta,
+                         int32_t pcDelta);
+  static void ReadDelta(CompactBufferReader& reader, uint32_t* nativeDelta,
+                        int32_t* pcDelta);
+
+  // Given a pointer into an array of NativeToBytecode (and a pointer to the end
+  // of the array), compute the number of entries that would be consume by
+  // outputting a run starting at this one.
+  static uint32_t ExpectedRunLength(const NativeToBytecode* entry,
+                                    const NativeToBytecode* end);
+
+  // Write a run, starting at the given NativeToBytecode entry, into the given
+  // buffer writer.
+  [[nodiscard]] static bool WriteRun(CompactBufferWriter& writer,
+                                     const IonEntry::ScriptList& scriptList,
+                                     uint32_t runLength,
+                                     const NativeToBytecode* entry);
+
+  // Delta Run entry formats are encoded little-endian:
+  //
+  //  byte 0
+  //  NNNN-BBB0
+  //      Single byte format.  nativeDelta in [0, 15], pcDelta in [0, 7]
+  //
+  static const uint32_t ENC1_MASK = 0x1;
+  static const uint32_t ENC1_MASK_VAL = 0x0;
+
+  static const uint32_t ENC1_NATIVE_DELTA_MAX = 0xf;
+  static const unsigned ENC1_NATIVE_DELTA_SHIFT = 4;
+
+  static const uint32_t ENC1_PC_DELTA_MASK = 0x0e;
+  static const int32_t ENC1_PC_DELTA_MAX = 0x7;
+  static const unsigned ENC1_PC_DELTA_SHIFT = 1;
+
+  //  byte 1    byte 0
+  //  NNNN-NNNN BBBB-BB01
+  //      Two-byte format.  nativeDelta in [0, 255], pcDelta in [0, 63]
+  //
+  static const uint32_t ENC2_MASK = 0x3;
+  static const uint32_t ENC2_MASK_VAL = 0x1;
+
+  static const uint32_t ENC2_NATIVE_DELTA_MAX = 0xff;
+  static const unsigned ENC2_NATIVE_DELTA_SHIFT = 8;
+
+  static const uint32_t ENC2_PC_DELTA_MASK = 0x00fc;
+  static const int32_t ENC2_PC_DELTA_MAX = 0x3f;
+  static const unsigned ENC2_PC_DELTA_SHIFT = 2;
+
+  //  byte 2    byte 1    byte 0
+  //  NNNN-NNNN NNNB-BBBB BBBB-B011
+  //      Three-byte format.  nativeDelta in [0, 2047], pcDelta in [-512, 511]
+  //
+  static const uint32_t ENC3_MASK = 0x7;
+  static const uint32_t ENC3_MASK_VAL = 0x3;
+
+  static const uint32_t ENC3_NATIVE_DELTA_MAX = 0x7ff;
+  static const unsigned ENC3_NATIVE_DELTA_SHIFT = 13;
+
+  static const uint32_t ENC3_PC_DELTA_MASK = 0x001ff8;
+  static const int32_t ENC3_PC_DELTA_MAX = 0x1ff;
+  static const int32_t ENC3_PC_DELTA_MIN = -ENC3_PC_DELTA_MAX - 1;
+  static const unsigned ENC3_PC_DELTA_SHIFT = 3;
+
+  //  byte 3    byte 2    byte 1    byte 0
+  //  NNNN-NNNN NNNN-NNNN BBBB-BBBB BBBB-B111
+  //      Three-byte format.  nativeDelta in [0, 65535],
+  //                          pcDelta in [-4096, 4095]
+  static const uint32_t ENC4_MASK = 0x7;
+  static const uint32_t ENC4_MASK_VAL = 0x7;
+
+  static const uint32_t ENC4_NATIVE_DELTA_MAX = 0xffff;
+  static const unsigned ENC4_NATIVE_DELTA_SHIFT = 16;
+
+  static const uint32_t ENC4_PC_DELTA_MASK = 0x0000fff8;
+  static const int32_t ENC4_PC_DELTA_MAX = 0xfff;
+  static const int32_t ENC4_PC_DELTA_MIN = -ENC4_PC_DELTA_MAX - 1;
+  static const unsigned ENC4_PC_DELTA_SHIFT = 3;
+
+  static bool IsDeltaEncodeable(uint32_t nativeDelta, int32_t pcDelta) {
+    return (nativeDelta <= ENC4_NATIVE_DELTA_MAX) &&
+           (pcDelta >= ENC4_PC_DELTA_MIN) && (pcDelta <= ENC4_PC_DELTA_MAX);
+  }
+
+ private:
+  const uint8_t* data_;
+  const uint8_t* end_;
+
+  // Unpacked state from jitcode entry.
+  uint32_t nativeOffset_;
+  uint8_t scriptDepth_;
+  const uint8_t* scriptPcStack_;
+  const uint8_t* deltaRun_;
+
+  void unpack();
+
+ public:
+  JitcodeRegionEntry(const uint8_t* data, const uint8_t* end)
+      : data_(data),
+        end_(end),
+        nativeOffset_(0),
+        scriptDepth_(0),
+        scriptPcStack_(nullptr),
+        deltaRun_(nullptr) {
+    MOZ_ASSERT(data_ < end_);
+    unpack();
+    MOZ_ASSERT(scriptPcStack_ < end_);
+    MOZ_ASSERT(deltaRun_ <= end_);
+  }
+
+  uint32_t nativeOffset() const { return nativeOffset_; }
+  uint32_t scriptDepth() const { return scriptDepth_; }
+
+  class ScriptPcIterator {
+   private:
+    const uint8_t* start_;
+    const uint8_t* end_;
+#ifdef DEBUG
+    uint32_t count_;
+#endif
+    uint32_t idx_;
+    const uint8_t* cur_;
+
+   public:
+    ScriptPcIterator(const uint8_t* start, const uint8_t* end, uint32_t count)
+        : start_(start),
+          end_(end),
+#ifdef DEBUG
+          count_(count),
+#endif
+          idx_(0),
+          cur_(start_) {
+    }
+
+    bool hasMore() const {
+      MOZ_ASSERT((idx_ == count_) == (cur_ == end_));
+      MOZ_ASSERT((idx_ < count_) == (cur_ < end_));
+      return cur_ < end_;
+    }
+
+    void readNext(uint32_t* scriptIdxOut, uint32_t* pcOffsetOut) {
+      MOZ_ASSERT(scriptIdxOut);
+      MOZ_ASSERT(pcOffsetOut);
+      MOZ_ASSERT(hasMore());
+
+      CompactBufferReader reader(cur_, end_);
+      ReadScriptPc(reader, scriptIdxOut, pcOffsetOut);
+
+      cur_ = reader.currentPosition();
+      MOZ_ASSERT(cur_ <= end_);
+
+      idx_++;
+      MOZ_ASSERT_IF(idx_ == count_, cur_ == end_);
+    }
+
+    void reset() {
+      idx_ = 0;
+      cur_ = start_;
+    }
+  };
+
+  ScriptPcIterator scriptPcIterator() const {
+    // End of script+pc sequence is the start of the delta run.
+    return ScriptPcIterator(scriptPcStack_, deltaRun_, scriptDepth_);
+  }
+
+  class DeltaIterator {
+   private:
+    const uint8_t* start_;
+    const uint8_t* end_;
+    const uint8_t* cur_;
+
+   public:
+    DeltaIterator(const uint8_t* start, const uint8_t* end)
+        : start_(start), end_(end), cur_(start) {}
+
+    bool hasMore() const {
+      MOZ_ASSERT(cur_ <= end_);
+      return cur_ < end_;
+    }
+
+    void readNext(uint32_t* nativeDeltaOut, int32_t* pcDeltaOut) {
+      MOZ_ASSERT(nativeDeltaOut != nullptr);
+      MOZ_ASSERT(pcDeltaOut != nullptr);
+
+      MOZ_ASSERT(hasMore());
+
+      CompactBufferReader reader(cur_, end_);
+      ReadDelta(reader, nativeDeltaOut, pcDeltaOut);
+
+      cur_ = reader.currentPosition();
+      MOZ_ASSERT(cur_ <= end_);
+    }
+
+    void reset() { cur_ = start_; }
+  };
+  DeltaIterator deltaIterator() const { return DeltaIterator(deltaRun_, end_); }
+
+  uint32_t findPcOffset(uint32_t queryNativeOffset,
+                        uint32_t startPcOffset) const;
+};
+
+class JitcodeIonTable {
+ private:
+  /* Variable length payload section "below" here. */
+  uint32_t numRegions_;
+  uint32_t regionOffsets_[1];
+
+  const uint8_t* payloadEnd() const {
+    return reinterpret_cast<const uint8_t*>(this);
+  }
+
+ public:
+  JitcodeIonTable() = delete;
+
+  uint32_t numRegions() const { return numRegions_; }
+
+  uint32_t regionOffset(uint32_t regionIndex) const {
+    MOZ_ASSERT(regionIndex < numRegions());
+    return regionOffsets_[regionIndex];
+  }
+
+  JitcodeRegionEntry regionEntry(uint32_t regionIndex) const {
+    const uint8_t* regionStart = payloadEnd() - regionOffset(regionIndex);
+    const uint8_t* regionEnd = payloadEnd();
+    if (regionIndex < numRegions_ - 1) {
+      regionEnd -= regionOffset(regionIndex + 1);
+    }
+    return JitcodeRegionEntry(regionStart, regionEnd);
+  }
+
+  uint32_t findRegionEntry(uint32_t offset) const;
+
+  const uint8_t* payloadStart() const {
+    // The beginning of the payload the beginning of the first region are the
+    // same.
+    return payloadEnd() - regionOffset(0);
+  }
+
+  [[nodiscard]] static bool WriteIonTable(
+      CompactBufferWriter& writer, const IonEntry::ScriptList& scriptList,
+      const NativeToBytecode* start, const NativeToBytecode* end,
+      uint32_t* tableOffsetOut, uint32_t* numRegionsOut);
+};
+
+}  // namespace jit
+}  // namespace js
+
+#endif /* jit_JitcodeMap_h */