embedded-data.h

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// Copyright 2018 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
#ifndef V8_SNAPSHOT_EMBEDDED_EMBEDDED_DATA_H_
#define V8_SNAPSHOT_EMBEDDED_EMBEDDED_DATA_H_
 
#include "src/base/macros.h"
#include "src/builtins/builtins.h"
#include "src/common/globals.h"
#include "src/execution/isolate.h"
#include "src/heap/code-range.h"
#include "src/objects/instruction-stream.h"
 
namespace v8 {
namespace internal {
 
class InstructionStream;
class Isolate;
 
using ReorderedBuiltinIndex = uint32_t;
 
// Wraps an off-heap instruction stream.
// TODO(jgruber,v8:6666): Remove this class.
class OffHeapInstructionStream final : public AllStatic {
 public:
  // Returns true, iff the given pc points into an off-heap instruction stream.
  static bool PcIsOffHeap(Isolate* isolate, Address pc);
 
  // If the address belongs to the embedded code blob, predictably converts it
  // to uint32 by calculating offset from the embedded code blob start and
  // returns true, and false otherwise.
  static bool TryGetAddressForHashing(Isolate* isolate, Address address,
                                      uint32_t* hashable_address);
 
  // Returns the corresponding builtin ID if lookup succeeds, and kNoBuiltinId
  // otherwise.
  static Builtin TryLookupCode(Isolate* isolate, Address address);
 
  // During snapshot creation, we first create an executable off-heap area
  // containing all off-heap code. The area is guaranteed to be contiguous.
  // Note that this only applies when building the snapshot, e.g. for
  // mksnapshot. Otherwise, off-heap code is embedded directly into the binary.
  static void CreateOffHeapOffHeapInstructionStream(Isolate* isolate,
                                                    uint8_t** code,
                                                    uint32_t* code_size,
                                                    uint8_t** data,
                                                    uint32_t* data_size);
  static void FreeOffHeapOffHeapInstructionStream(uint8_t* code,
                                                  uint32_t code_size,
                                                  uint8_t* data,
                                                  uint32_t data_size);
};
 
class EmbeddedData final {
 public:
  // Create the embedded blob from the given Isolate's heap state.
  static EmbeddedData NewFromIsolate(Isolate* isolate);
 
  // Returns the global embedded blob (usually physically located in .text and
  // .rodata).
  static EmbeddedData FromBlob() {
    return EmbeddedData(Isolate::CurrentEmbeddedBlobCode(),
                        Isolate::CurrentEmbeddedBlobCodeSize(),
                        Isolate::CurrentEmbeddedBlobData(),
                        Isolate::CurrentEmbeddedBlobDataSize());
  }
 
  // Returns a potentially remapped embedded blob (see also
  // MaybeRemapEmbeddedBuiltinsIntoCodeRange).
  static EmbeddedData FromBlob(Isolate* isolate) {
    return EmbeddedData(
        isolate->embedded_blob_code(), isolate->embedded_blob_code_size(),
        isolate->embedded_blob_data(), isolate->embedded_blob_data_size());
  }
 
  // Returns a potentially remapped embedded blob (see also
  // MaybeRemapEmbeddedBuiltinsIntoCodeRange).
  static EmbeddedData FromBlob(CodeRange* code_range) {
    return EmbeddedData(code_range->embedded_blob_code_copy(),
                        Isolate::CurrentEmbeddedBlobCodeSize(),
                        Isolate::CurrentEmbeddedBlobData(),
                        Isolate::CurrentEmbeddedBlobDataSize());
  }
 
  // When short builtin calls optimization is enabled for the Isolate, there
  // will be two builtins instruction streams executed: the embedded one and
  // the one un-embedded into the per-Isolate code range. In most of the cases,
  // the per-Isolate instructions will be used but in some cases (like builtin
  // calls from Wasm) the embedded instruction stream could be used.  If the
  // requested PC belongs to the embedded code blob - it'll be returned, and
  // the per-Isolate blob otherwise.
  // See http://crbug.com/v8/11527 for details.
  static EmbeddedData FromBlobForPc(Isolate* isolate,
                                    Address maybe_builtin_pc) {
    EmbeddedData d = EmbeddedData::FromBlob(isolate);
    if (d.IsInCodeRange(maybe_builtin_pc)) return d;
    if (isolate->is_short_builtin_calls_enabled()) {
      EmbeddedData global_d = EmbeddedData::FromBlob();
      // If the pc does not belong to the embedded code blob we should be using
      // the un-embedded one.
      if (global_d.IsInCodeRange(maybe_builtin_pc)) return global_d;
    }
#if defined(V8_COMPRESS_POINTERS_IN_SHARED_CAGE) && \
    defined(V8_SHORT_BUILTIN_CALLS)
    // When shared pointer compression cage is enabled and it has the embedded
    // code blob copy then it could have been used regardless of whether the
    // isolate uses it or knows about it or not (see
    // InstructionStream::OffHeapInstructionStart()).
    // So, this blob has to be checked too.
    CodeRange* code_range = IsolateGroup::current()->GetCodeRange();
    if (code_range && code_range->embedded_blob_code_copy() != nullptr) {
      EmbeddedData remapped_d = EmbeddedData::FromBlob(code_range);
      // If the pc does not belong to the embedded code blob we should be
      // using the un-embedded one.
      if (remapped_d.IsInCodeRange(maybe_builtin_pc)) return remapped_d;
    }
#endif  // defined(V8_COMPRESS_POINTERS_IN_SHARED_CAGE) &&
        // defined(V8_SHORT_BUILTIN_CALLS)
    return d;
  }
 
  const uint8_t* code() const { return code_; }
  uint32_t code_size() const { return code_size_; }
  const uint8_t* data() const { return data_; }
  uint32_t data_size() const { return data_size_; }
 
  bool IsInCodeRange(Address pc) const {
    Address start = reinterpret_cast<Address>(code_);
    return (start <= pc) && (pc < start + code_size_);
  }
 
  void Dispose() {
    delete[] code_;
    code_ = nullptr;
    delete[] data_;
    data_ = nullptr;
  }
 
  inline Address InstructionStartOf(Builtin builtin) const;
  inline Address InstructionEndOf(Builtin builtin) const;
  inline uint32_t InstructionSizeOf(Builtin builtin) const;
  inline Address InstructionStartOfBytecodeHandlers() const;
  inline Address InstructionEndOfBytecodeHandlers() const;
  inline Address MetadataStartOf(Builtin builtin) const;
 
  uint32_t AddressForHashing(Address addr) {
    DCHECK(IsInCodeRange(addr));
    Address start = reinterpret_cast<Address>(code_);
    return static_cast<uint32_t>(addr - start);
  }
 
  // Padded with kCodeAlignment.
  inline uint32_t PaddedInstructionSizeOf(Builtin builtin) const;
 
  size_t CreateEmbeddedBlobDataHash() const;
  size_t CreateEmbeddedBlobCodeHash() const;
  size_t EmbeddedBlobDataHash() const {
    return *reinterpret_cast<const size_t*>(data_ +
                                            EmbeddedBlobDataHashOffset());
  }
  size_t EmbeddedBlobCodeHash() const {
    return *reinterpret_cast<const size_t*>(data_ +
                                            EmbeddedBlobCodeHashOffset());
  }
 
  size_t IsolateHash() const {
    return *reinterpret_cast<const size_t*>(data_ + IsolateHashOffset());
  }
 
  Builtin TryLookupCode(Address address) const;
 
  // Blob layout information for a single instruction stream.
  struct LayoutDescription {
    // The offset and (unpadded) length of this builtin's instruction area
    // from the start of the embedded code section.
    uint32_t instruction_offset;
    uint32_t instruction_length;
    // The offset of this builtin's metadata area from the start of the
    // embedded data section.
    uint32_t metadata_offset;
  };
  static_assert(offsetof(LayoutDescription, instruction_offset) ==
                0 * kUInt32Size);
  static_assert(offsetof(LayoutDescription, instruction_length) ==
                1 * kUInt32Size);
  static_assert(offsetof(LayoutDescription, metadata_offset) ==
                2 * kUInt32Size);
 
  // The embedded code section stores builtins in the so-called
  // 'embedded snapshot order' which is usually different from the order
  // as defined by the Builtins enum ('builtin id order'), and determined
  // through an algorithm based on collected execution profiles. The
  // BuiltinLookupEntry struct maps from the 'embedded snapshot order' to
  // the 'builtin id order' and additionally keeps a copy of instruction_end for
  // each builtin since it is convenient for binary search.
  struct BuiltinLookupEntry {
    // The end offset (including padding) of builtin, the end_offset field
    // should be in ascending order in the array in snapshot, because we will
    // use it in TryLookupCode. It should be equal to
    // LayoutDescription[builtin_id].instruction_offset +
    // PadAndAlignCode(length)
    uint32_t end_offset;
    // The id of builtin.
    uint32_t builtin_id;
  };
  static_assert(offsetof(BuiltinLookupEntry, end_offset) == 0 * kUInt32Size);
  static_assert(offsetof(BuiltinLookupEntry, builtin_id) == 1 * kUInt32Size);
 
  Builtin GetBuiltinId(ReorderedBuiltinIndex embedded_index) const;
 
  // The layout of the blob is as follows:
  //
  // data:
  // [0] hash of the data section
  // [1] hash of the code section
  // [2] hash of embedded-blob-relevant heap objects
  // [3] layout description of builtin 0
  // ... layout descriptions (builtin id order)
  // [n] builtin lookup table where entries are sorted by offset_end in
  //     ascending order. (embedded snapshot order)
  // [x] metadata section of builtin 0
  // ... metadata sections (builtin id order)
  //
  // code:
  // [0] instruction section of builtin 0
  // ... instruction sections (embedded snapshot order)
 
  static constexpr uint32_t kTableSize = Builtins::kBuiltinCount;
  static constexpr uint32_t EmbeddedBlobDataHashOffset() { return 0; }
  static constexpr uint32_t EmbeddedBlobDataHashSize() { return kSizetSize; }
  static constexpr uint32_t EmbeddedBlobCodeHashOffset() {
    return EmbeddedBlobDataHashOffset() + EmbeddedBlobDataHashSize();
  }
  static constexpr uint32_t EmbeddedBlobCodeHashSize() { return kSizetSize; }
  static constexpr uint32_t IsolateHashOffset() {
    return EmbeddedBlobCodeHashOffset() + EmbeddedBlobCodeHashSize();
  }
  static constexpr uint32_t IsolateHashSize() { return kSizetSize; }
  static constexpr uint32_t LayoutDescriptionTableOffset() {
    return IsolateHashOffset() + IsolateHashSize();
  }
  static constexpr uint32_t LayoutDescriptionTableSize() {
    return sizeof(struct LayoutDescription) * kTableSize;
  }
  static constexpr uint32_t BuiltinLookupEntryTableOffset() {
    return LayoutDescriptionTableOffset() + LayoutDescriptionTableSize();
  }
  static constexpr uint32_t BuiltinLookupEntryTableSize() {
    return sizeof(struct BuiltinLookupEntry) * kTableSize;
  }
  static constexpr uint32_t FixedDataSize() {
    return BuiltinLookupEntryTableOffset() + BuiltinLookupEntryTableSize();
  }
  // The variable-size data section starts here.
  static constexpr uint32_t RawMetadataOffset() { return FixedDataSize(); }
 
  // Code is in its own dedicated section.
  static constexpr uint32_t RawCodeOffset() { return 0; }
 
 private:
  EmbeddedData(const uint8_t* code, uint32_t code_size, const uint8_t* data,
               uint32_t data_size)
      : code_(code), code_size_(code_size), data_(data), data_size_(data_size) {
    DCHECK_NOT_NULL(code);
    DCHECK_LT(0, code_size);
    DCHECK_NOT_NULL(data);
    DCHECK_LT(0, data_size);
  }
 
  const uint8_t* RawCode() const { return code_ + RawCodeOffset(); }
 
  const LayoutDescription& LayoutDescription(Builtin builtin) const {
    const struct LayoutDescription* descs =
        reinterpret_cast<const struct LayoutDescription*>(
            data_ + LayoutDescriptionTableOffset());
    return descs[static_cast<int>(builtin)];
  }
 
  const BuiltinLookupEntry* BuiltinLookupEntry(
      ReorderedBuiltinIndex index) const {
    const struct BuiltinLookupEntry* entries =
        reinterpret_cast<const struct BuiltinLookupEntry*>(
            data_ + BuiltinLookupEntryTableOffset());
    return entries + index;
  }
 
  const uint8_t* RawMetadata() const { return data_ + RawMetadataOffset(); }
 
  static constexpr int PadAndAlignCode(int size) {
    // Ensure we have at least one byte trailing the actual builtin
    // instructions which we can later fill with int3.
    return RoundUp<kCodeAlignment>(size + 1);
  }
  static constexpr int PadAndAlignData(int size) {
    // Ensure we have at least one byte trailing the actual builtin
    // instructions which we can later fill with int3.
    return RoundUp<InstructionStream::kMetadataAlignment>(size);
  }
 
  void PrintStatistics() const;
 
  // The code section contains instruction streams. It is guaranteed to have
  // execute permissions, and may have read permissions.
  const uint8_t* code_;
  uint32_t code_size_;
 
  // The data section contains both descriptions of the code section (hashes,
  // offsets, sizes) and metadata describing InstructionStream objects (see
  // InstructionStream::MetadataStart()). It is guaranteed to have read
  // permissions.
  const uint8_t* data_;
  uint32_t data_size_;
};
 
}  // namespace internal
}  // namespace v8
 
#endif  // V8_SNAPSHOT_EMBEDDED_EMBEDDED_DATA_H_