// Copyright (c) 2011 The Chromium 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 COURGETTE_ASSEMBLY_PROGRAM_H_
#define COURGETTE_ASSEMBLY_PROGRAM_H_

#include <stddef.h>
#include <stdint.h>

#include <map>
#include <memory>

#include "base/callback_forward.h"
#include "base/macros.h"
#include "base/memory/free_deleter.h"
#include "courgette/courgette.h"
#include "courgette/image_utils.h"
#include "courgette/label_manager.h"
#include "courgette/memory_allocator.h"

namespace courgette {

class EncodedProgram;

// Opcodes of simple assembly language
enum OP {
  ORIGIN,         // ORIGIN <rva> - set current address for assembly.
  MAKEPERELOCS,   // Generates a base relocation table.
  MAKEELFRELOCS,  // Generates a base relocation table.
  DEFBYTE,        // DEFBYTE <value> - emit a byte literal.
  REL32,          // REL32 <label> - emit a rel32 encoded reference to 'label'.
  ABS32,          // ABS32 <label> - emit an abs32 encoded reference to 'label'.
  REL32ARM,       // REL32ARM <c_op> <label> - arm-specific rel32 reference
  MAKEELFARMRELOCS,  // Generates a base relocation table.
  DEFBYTES,       // Emits any number of byte literals
  ABS64,          // ABS64 <label> - emit an abs64 encoded reference to 'label'.
  LAST_OP
};

// Base class for instructions.  Because we have so many instructions we want to
// keep them as small as possible.  For this reason we avoid virtual functions.
class Instruction {
 public:
  OP op() const { return static_cast<OP>(op_); }

 protected:
  explicit Instruction(OP op) : op_(op), info_(0) {}
  Instruction(OP op, unsigned int info) : op_(op), info_(info) {}

  uint32_t op_ : 4;     // A few bits to store the OP code.
  uint32_t info_ : 28;  // Remaining bits in first word available to subclass.

 private:
  DISALLOW_COPY_AND_ASSIGN(Instruction);
};

// An interface to receive emitted instructions parsed from an executable.
class InstructionReceptor {
 public:
  InstructionReceptor() = default;
  virtual ~InstructionReceptor() = default;

  // Generates an entire base relocation table.
  virtual CheckBool EmitPeRelocs() = 0;

  // Generates an ELF style relocation table for X86.
  virtual CheckBool EmitElfRelocation() = 0;

  // Generates an ELF style relocation table for ARM.
  virtual CheckBool EmitElfARMRelocation() = 0;

  // Following instruction will be assembled at address 'rva'.
  virtual CheckBool EmitOrigin(RVA rva) = 0;

  // Generates a single byte of data or machine instruction.
  virtual CheckBool EmitSingleByte(uint8_t byte) = 0;

  // Generates multiple bytes of data or machine instructions.
  virtual CheckBool EmitMultipleBytes(const uint8_t* bytes, size_t len) = 0;

  // Generates a 4-byte relative reference to address of 'label'.
  virtual CheckBool EmitRel32(Label* label) = 0;

  // Generates a 4-byte relative reference to address of 'label' for ARM.
  virtual CheckBool EmitRel32ARM(uint16_t op,
                                 Label* label,
                                 const uint8_t* arm_op,
                                 uint16_t op_size) = 0;

  // Generates a 4-byte absolute reference to address of 'label'.
  virtual CheckBool EmitAbs32(Label* label) = 0;

  // Generates an 8-byte absolute reference to address of 'label'.
  virtual CheckBool EmitAbs64(Label* label) = 0;

 private:
  DISALLOW_COPY_AND_ASSIGN(InstructionReceptor);
};

// An AssemblyProgram is the result of disassembling an executable file.
//
// * The disassembler creates labels in the AssemblyProgram and emits
//   'Instructions'.
// * The disassembler then calls DefaultAssignIndexes to assign
//   addresses to positions in the address tables.
// * [Optional step]
// * At this point the AssemblyProgram can be converted into an
//   EncodedProgram and serialized to an output stream.
// * Later, the EncodedProgram can be deserialized and assembled into
//   the original file.
//
// The optional step is to modify the AssemblyProgram.  One form of modification
// is to assign indexes in such a way as to make the EncodedProgram for this
// AssemblyProgram look more like the EncodedProgram for some other
// AssemblyProgram.  The modification process should call UnassignIndexes, do
// its own assignment, and then call AssignRemainingIndexes to ensure all
// indexes are assigned.

class AssemblyProgram {
 public:
  using LabelHandler = base::Callback<void(Label*)>;
  using LabelHandlerMap = std::map<OP, LabelHandler>;

  // A callback for GenerateInstructions() to emit instructions. The first
  // argument (AssemblyProgram*) is provided for Label-related feature access.
  // The second argument (InstructionReceptor*) is a receptor for instructions.
  // The callback (which gets called in 2 passes) should return true on success,
  // and false otherwise.
  using InstructionGenerator =
      base::Callback<CheckBool(AssemblyProgram*, InstructionReceptor*)>;

  AssemblyProgram(ExecutableType kind, uint64_t image_base);
  ~AssemblyProgram();

  ExecutableType kind() const { return kind_; }

  // Traverses RVAs in |abs32_visitor| and |rel32_visitor| to precompute Labels.
  void PrecomputeLabels(RvaVisitor* abs32_visitor, RvaVisitor* rel32_visitor);

  // Removes underused Labels. Thresholds used (0 = no trimming) is
  // architecture-dependent.
  void TrimLabels();

  void UnassignIndexes();
  void DefaultAssignIndexes();
  void AssignRemainingIndexes();

  // Looks up abs32 label. Returns null if none found.
  Label* FindAbs32Label(RVA rva);

  // Looks up rel32 label. Returns null if none found.
  Label* FindRel32Label(RVA rva);

  std::unique_ptr<EncodedProgram> Encode() const;

  // For each |instruction| in |instructions_|, looks up its opcode from
  // |handler_map| for a handler. If a handler exists, invoke it by passing the
  // |instruction|'s label. We assume that |handler_map| has correct keys, i.e.,
  // opcodes for an instruction that have label.
  void HandleInstructionLabels(const LabelHandlerMap& handler_map) const;

  // Calls |gen| in 2 passes to emit instructions. In pass 1 we provide a
  // receptor to count space requirement. In pass 2 we provide a receptor to
  // store instructions.
  CheckBool GenerateInstructions(const InstructionGenerator& gen);

  // TODO(huangs): Implement these in InstructionStoreReceptor.
  // Instructions will be assembled in the order they are emitted.

  // Generates an entire base relocation table.
  CheckBool EmitPeRelocs() WARN_UNUSED_RESULT;

  // Generates an ELF style relocation table for X86.
  CheckBool EmitElfRelocation() WARN_UNUSED_RESULT;

  // Generates an ELF style relocation table for ARM.
  CheckBool EmitElfARMRelocation() WARN_UNUSED_RESULT;

  // Following instruction will be assembled at address 'rva'.
  CheckBool EmitOrigin(RVA rva) WARN_UNUSED_RESULT;

  // Generates a single byte of data or machine instruction.
  CheckBool EmitSingleByte(uint8_t byte) WARN_UNUSED_RESULT;

  // Generates multiple bytes of data or machine instructions.
  CheckBool EmitMultipleBytes(const uint8_t* bytes,
                              size_t len) WARN_UNUSED_RESULT;

  // Generates a 4-byte relative reference to address of 'label'.
  CheckBool EmitRel32(Label* label) WARN_UNUSED_RESULT;

  // Generates a 4-byte relative reference to address of 'label' for ARM.
  CheckBool EmitRel32ARM(uint16_t op,
                         Label* label,
                         const uint8_t* arm_op,
                         uint16_t op_size) WARN_UNUSED_RESULT;

  // Generates a 4-byte absolute reference to address of 'label'.
  CheckBool EmitAbs32(Label* label) WARN_UNUSED_RESULT;

  // Generates an 8-byte absolute reference to address of 'label'.
  CheckBool EmitAbs64(Label* label) WARN_UNUSED_RESULT;

 private:
  using InstructionVector = NoThrowBuffer<Instruction*>;

  using ScopedInstruction =
      std::unique_ptr<Instruction, UncheckedDeleter<Instruction>>;

  CheckBool Emit(ScopedInstruction instruction) WARN_UNUSED_RESULT;
  CheckBool EmitShared(Instruction* instruction) WARN_UNUSED_RESULT;

  static const int kLabelLowerLimit;

  // Looks up a label or creates a new one.  Might return NULL.
  Label* FindLabel(RVA rva, RVAToLabel* labels);

  // Sharing instructions that emit a single byte saves a lot of space.
  Instruction* GetByteInstruction(uint8_t byte);

  const ExecutableType kind_;
  const uint64_t image_base_;  // Desired or mandated base address of image.

  std::unique_ptr<Instruction* [], base::FreeDeleter> byte_instruction_cache_;

  InstructionVector instructions_;  // All the instructions in program.

  // Storage and lookup of Labels associated with target addresses. We use
  // separate abs32 and rel32 labels.
  LabelManager abs32_label_manager_;
  LabelManager rel32_label_manager_;

  DISALLOW_COPY_AND_ASSIGN(AssemblyProgram);
};

// Converts |program| into encoded form, returning it as |*output|.
// Returns C_OK if succeeded, otherwise returns an error status and sets
// |*output| to null.
Status Encode(const AssemblyProgram& program,
              std::unique_ptr<EncodedProgram>* output);

}  // namespace courgette

#endif  // COURGETTE_ASSEMBLY_PROGRAM_H_