Reland Implement .eh_frame writer and disassembler.

src/eh-frame.h

 // Copyright 2016 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_EH_FRAME_H_
 #define V8_EH_FRAME_H_
 
-#include <cstdint>
+#include "src/macro-assembler.h"
 
 namespace v8 {
 namespace internal {
 
-class Code;
+class EhFrameWriter {
+ public:
+  enum class DwarfOpcodes : byte {
+    kNop = 0x00,
+    kAdvanceLoc1 = 0x02,
+    kAdvanceLoc2 = 0x03,
+    kAdvanceLoc4 = 0x04,
+    kSameValue = 0x08,
+    kDefCfa = 0x0c,
+    kDefCfaRegister = 0x0d,
+    kDefCfaOffset = 0x0e,
+    kOffsetExtendedSf = 0x11,
+  };
+
+  enum DwarfEncodingSpecifiers : byte {
+    kUData4 = 0x03,
+    kSData4 = 0x0b,
+    kPcRel = 0x10,
+    kDataRel = 0x30,
+    kOmit = 0xff,
+  };
+
+  static const int kLocationTag = 1;
+  static const int kLocationMask = 0x3f;
+  static const int kLocationMaskSize = 6;
+
+  static const int kSavedRegisterTag = 2;
+  static const int kSavedRegisterMask = 0x3f;
+  static const int kSavedRegisterMaskSize = 6;
+
+  static const int kFollowInitialRuleTag = 3;
+  static const int kFollowInitialRuleMask = 0x3f;
+  static const int kFollowInitialRuleMaskSize = 6;
+
+  static const int kProcedureAddressOffsetInFde = 2 * kInt32Size;
+  static const int kProcedureSizeOffsetInFde = 3 * kInt32Size;
+
+  static const int kInitialStateOffsetInCIE = 19;
+  static const int kEhFrameTerminatorSize = 4;
+
+  static const int kDataAlignmentFactor;
+
+  EhFrameWriter();
+
+  void AdvanceLocation(int pc_offset);
+
+  // The <base_address> is the one to which all <offset>s in SaveRegisterToStack
+  // directives are relative. It is given by <base_register> + <base_offset>.
+  void SetBaseAddressRegister(Register base_register);
+  void SetBaseAddressOffset(int base_offset);
+  void IncreaseBaseAddressOffset(int base_delta) {
+    SetBaseAddressOffset(base_offset_ + base_delta);
+  }
+  void SetBaseAddressRegisterAndOffset(Register base_register, int base_offset);
+
+  // Register saved at location <base_address> + <offset>
+  void RecordRegisterSavedToStack(Register name, int offset) {
+    RecordRegisterSavedToStack(RegisterToDwarfCode(name), offset);
+  }
+
+  void RecordRegisterIsValid(Register name);
+
+  void RecordRegisterFollowsInitialRule(Register name);
+
+  void Finish(int code_size);
+
+  // Remember to call Finish() before GetEhFrame().
+  //
+  // The EhFrameWriter instance owns the buffer pointed by
+  // CodeDesc::unwinding_info, and must outlive any use of the CodeDesc.
+  void GetEhFrame(CodeDesc* desc);
+
+  int last_pc_offset() const { return last_pc_offset_; }
+  Register base_register() const { return base_register_; }
+  int base_offset() const { return base_offset_; }
+
+ private:
+  static const uint32_t kInt32Placeholder = 0xdeadc0de;
+
+  static int RegisterToDwarfCode(Register name);
+
+  void WriteSLEB128(int32_t value);
+  void WriteULEB128(uint32_t value);
+
+  void WriteByte(byte value) { eh_frame_buffer_.push_back(value); }
+  void WriteOpcode(DwarfOpcodes opcode) {
+    WriteByte(static_cast<byte>(opcode));
+  }
+  void WriteBytes(const byte* start, int size) {
+    eh_frame_buffer_.insert(eh_frame_buffer_.end(), start, start + size);
+  }
+  void WriteInt16(uint16_t value) {
+    WriteBytes(reinterpret_cast<const byte*>(&value), sizeof(value));
+  }
+  void WriteInt32(uint32_t value) {
+    WriteBytes(reinterpret_cast<const byte*>(&value), sizeof(value));
+  }
+  void PatchInt32(int base_offset, uint32_t value) {
+    DCHECK_EQ(ReadUnalignedUInt32(eh_frame_buffer_.data() + base_offset),
+              kInt32Placeholder);
+    DCHECK_LT(base_offset + kInt32Size, eh_frame_offset());
+    WriteUnalignedUInt32(eh_frame_buffer_.data() + base_offset, value);
+  }
+
+  void WriteCIE();
+  void WriteReturnAddressRegisterCode();
+  void WriteInitialStateInCIE();
+  void WriteFDEHeader();
+  void WritePaddingTo8ByteAlignment();
+
+  // Internal version that directly accepts a DWARF register code, needed for
+  // handling pseudoregisters on some platforms, such as x64.
+  void RecordRegisterSavedToStack(int register_code, int offset);
+
+  int eh_frame_offset() const {
+    return static_cast<int>(eh_frame_buffer_.size());
+  }
+
+  int fde_offset() const { return cie_size_; }
+
+  int procedure_address_offset() const {
+    return fde_offset() + kProcedureAddressOffsetInFde;
+  }
+
+  int procedure_size_offset() const {
+    return fde_offset() + kProcedureSizeOffsetInFde;
+  }
+
+  int cie_size_;
+  int last_pc_offset_;
+  bool eh_frame_finalised_;
+  Register base_register_;
+  int base_offset_;
+  std::vector<byte> eh_frame_buffer_;
+};
+
+class EhFrameIterator {
+ public:
+  explicit EhFrameIterator(EhFrameWriter* writer);

[rmcilroy, 2016/07/06 13:59:30]

Why does this take a frame writer? It should take the output of the  frame
written by Finish, it seems strange to iterate over a writer

[Stefano Sanfilippo, 2016/07/06 16:54:50]

In order to extract the buffer from the EhFrameWriter, one must pass through a
CodeDesc, so this seemed a nice shortcut, but I agree it's not immediate what's
going on. Removed and refactored uses.

+
+  EhFrameIterator(const byte* start, const byte* end)
+      : start_(start), next_(start), end_(end) {
+    DCHECK_LE(start, end);
+  }
+
+  void SkipCIE() {
+    DCHECK_EQ(next_, start_);
+    next_ += ReadUnalignedUInt32(next_) + kInt32Size;
+  }
+
+  void SkipToFDEDirectives() {
+    SkipCIE();
+    // Skip the FDE header.
+    Skip(4 * kInt32Size + 1);

[rmcilroy, 2016/07/06 13:59:30]

You should have a constant for the size of the FDE header in EhFrame

[Stefano Sanfilippo, 2016/07/06 16:54:50]

Done.

+  }
+
+  void Skip(int how_many) {
+    next_ += how_many;
+    DCHECK_LE(next_, end_);
+  }
+
+  uint32_t GetNextUInt32() { return GetNextIntegral<uint32_t>(); }
+  uint16_t GetNextUInt16() { return GetNextIntegral<uint16_t>(); }
+  byte GetNextByte() { return GetNextIntegral<byte>(); }
+  EhFrameWriter::DwarfOpcodes GetNextOpcode() {
+    return static_cast<EhFrameWriter::DwarfOpcodes>(GetNextByte());
+  }
+
+  uint32_t GetNextULEB128();
+  int32_t GetNextSLEB128();
+
+  bool ReachedEnd() const {

[rmcilroy, 2016/07/06 13:59:30]

nit - Done() or Finished() is the usual naming

[Stefano Sanfilippo, 2016/07/06 16:54:50]

Done.

+    DCHECK_LE(next_, end_);
+    return next_ == end_;
+  }
+
+  const void* current_address() const {
+    return reinterpret_cast<const void*>(next_);
+  }
+  int GetCurrentOffset() const {

[rmcilroy, 2016/07/06 13:59:30]

newline

[Stefano Sanfilippo, 2016/07/06 16:54:50]

Done.

+    DCHECK_GE(next_, start_);
+    return static_cast<int>(next_ - start_);
+  }
+  int GetBufferSize() { return static_cast<int>(end_ - start_); }
+
+ private:
+  static uint32_t DecodeULEB128(const byte* encoded, int* encoded_size);
+  static int32_t DecodeSLEB128(const byte* encoded, int* encoded_size);
+
+  template <typename T>
+  T GetNextIntegral() {

[rmcilroy, 2016/07/06 13:59:30]

/s/Integral/Value

[Stefano Sanfilippo, 2016/07/06 16:54:50]

Done.

+    T result;
+    DCHECK_LE(next_ + sizeof(result), end_);
+    result = ReadUnalignedValue<T>(next_);
+    next_ += sizeof(result);
+    return result;
+  }
+
+  const byte* start_;
+  const byte* next_;
+  const byte* end_;
+
+  friend class EhFrameIteratorTest;
+};
+
+#ifdef ENABLE_DISASSEMBLER
+
+class EhFrameDisassembler final {
+ public:
+  EhFrameDisassembler(const byte* start, const byte* end)
+      : start_(start), end_(end) {
+    DCHECK_LE(start, end);
+  }
+
+  void DisassembleToStream(std::ostream& stream);  // NOLINT
+
+ private:
+  static void DumpDWARFDirectives(std::ostream& stream,  // NOLINT
+                                  const byte* start, const byte* end);
+
+  static const char* DwarfRegisterCodeToString(int code);
+
+  const byte* start_;
+  const byte* end_;
+};
+
+#endif
 
 class EhFrameHdr final {
  public:
   static const int kRecordSize = 20;
-  static const int kCIESize;
-
-  explicit EhFrameHdr(Code* code);
+
+  EhFrameHdr(int code_size, int eh_frame_size, int cie_size);
+  static EhFrameHdr CreateEmptyHeader();
 
   int32_t offset_to_eh_frame() const { return offset_to_eh_frame_; }
   uint32_t lut_entries_number() const { return lut_entries_number_; }
   int32_t offset_to_procedure() const { return offset_to_procedure_; }
   int32_t offset_to_fde() const { return offset_to_fde_; }
 
  private:
+  static const int kEhFrameHdrVersion = 1;
+
+  EhFrameHdr() {}
+
   uint8_t version_;
   uint8_t eh_frame_ptr_encoding_;
   uint8_t lut_size_encoding_;
   uint8_t lut_entries_encoding_;
   int32_t offset_to_eh_frame_;
   uint32_t lut_entries_number_;
   int32_t offset_to_procedure_;
   int32_t offset_to_fde_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif