path: root/js/src/jit/JitcodeMap.h

/* -*- 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 */