src/assembler.h

//===- subzero/src/assembler.h - Integrated assembler -----------*- C++ -*-===//
// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
//
// Modified by the Subzero authors.
//
//===----------------------------------------------------------------------===//
//
//                        The Subzero Code Generator
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file declares the Assembler base class.  Instructions are assembled
// by architecture-specific assemblers that derive from this base class.
// This base class manages buffers and fixups for emitting code, etc.
//
//===----------------------------------------------------------------------===//

#ifndef SUBZERO_SRC_ASSEMBLER_H
#define SUBZERO_SRC_ASSEMBLER_H

#include "IceDefs.h"
#include "IceFixups.h"

namespace Ice {

// Assembler buffers are used to emit binary code. They grow on demand.
class AssemblerBuffer {
  AssemblerBuffer(const AssemblerBuffer &) = delete;
  AssemblerBuffer &operator=(const AssemblerBuffer &) = delete;

public:
  AssemblerBuffer(Assembler &);
  ~AssemblerBuffer();

  // Basic support for emitting, loading, and storing.
  template <typename T> void Emit(T value) {
    assert(HasEnsuredCapacity());
    *reinterpret_cast<T *>(cursor_) = value;
    cursor_ += sizeof(T);
  }

  template <typename T> T Load(intptr_t position) const {
    assert(position >= 0 &&
           position <= (Size() - static_cast<intptr_t>(sizeof(T))));
    return *reinterpret_cast<T *>(contents_ + position);
  }

  template <typename T> void Store(intptr_t position, T value) {
    assert(position >= 0 &&
           position <= (Size() - static_cast<intptr_t>(sizeof(T))));
    *reinterpret_cast<T *>(contents_ + position) = value;
  }

  // Emit a fixup at the current location.
  void EmitFixup(AssemblerFixup *fixup) {
    fixup->set_position(Size());
  }

  // Get the size of the emitted code.
  intptr_t Size() const { return cursor_ - contents_; }
  uintptr_t contents() const { return contents_; }

// To emit an instruction to the assembler buffer, the EnsureCapacity helper
// must be used to guarantee that the underlying data area is big enough to
// hold the emitted instruction. Usage:
//
//     AssemblerBuffer buffer;
//     AssemblerBuffer::EnsureCapacity ensured(&buffer);
//     ... emit bytes for single instruction ...

#ifndef NDEBUG
  class EnsureCapacity {
    EnsureCapacity(const EnsureCapacity &) = delete;
    EnsureCapacity &operator=(const EnsureCapacity &) = delete;

  public:
    explicit EnsureCapacity(AssemblerBuffer *buffer);
    ~EnsureCapacity();

  private:
    AssemblerBuffer *buffer_;
    intptr_t gap_;

    intptr_t ComputeGap() { return buffer_->Capacity() - buffer_->Size(); }
  };

  bool has_ensured_capacity_;
  bool HasEnsuredCapacity() const { return has_ensured_capacity_; }
#else  // NDEBUG
  class EnsureCapacity {
    EnsureCapacity(const EnsureCapacity &) = delete;
    EnsureCapacity &operator=(const EnsureCapacity &) = delete;

  public:
    explicit EnsureCapacity(AssemblerBuffer *buffer) {
      if (buffer->cursor() >= buffer->limit())
        buffer->ExtendCapacity();
    }
  };

  // When building the C++ tests, assertion code is enabled. To allow
  // asserting that the user of the assembler buffer has ensured the
  // capacity needed for emitting, we add a dummy method in non-debug mode.
  bool HasEnsuredCapacity() const { return true; }
#endif // NDEBUG

  // Returns the position in the instruction stream.
  intptr_t GetPosition() const { return cursor_ - contents_; }

  // Create and track a fixup in the current function.
  AssemblerFixup *createFixup(FixupKind Kind, const Constant *Value);

  const FixupRefList &fixups() const { return fixups_; }

private:
  // The limit is set to kMinimumGap bytes before the end of the data area.
  // This leaves enough space for the longest possible instruction and allows
  // for a single, fast space check per instruction.
  static const intptr_t kMinimumGap = 32;

  uintptr_t contents_;
  uintptr_t cursor_;
  uintptr_t limit_;
  Assembler &assembler_;
  // List of pool-allocated fixups relative to the current function.
  FixupRefList fixups_;

  uintptr_t cursor() const { return cursor_; }
  uintptr_t limit() const { return limit_; }
  intptr_t Capacity() const {
    assert(limit_ >= contents_);
    return (limit_ - contents_) + kMinimumGap;
  }

  // Compute the limit based on the data area and the capacity. See
  // description of kMinimumGap for the reasoning behind the value.
  static uintptr_t ComputeLimit(uintptr_t data, intptr_t capacity) {
    return data + capacity - kMinimumGap;
  }

  void ExtendCapacity();
};

class Assembler {
  Assembler(const Assembler &) = delete;
  Assembler &operator=(const Assembler &) = delete;

public:
  Assembler() : buffer_(*this) {}
  virtual ~Assembler() {}

  // Allocate a chunk of bytes using the per-Assembler allocator.
  uintptr_t AllocateBytes(size_t bytes) {
    // For now, alignment is not related to NaCl bundle alignment, since
    // the buffer's GetPosition is relative to the base. So NaCl bundle
    // alignment checks can be relative to that base. Later, the buffer
    // will be copied out to a ".text" section (or an in memory-buffer
    // that can be mprotect'ed with executable permission), and that
    // second buffer should be aligned for NaCl.
    const size_t Alignment = 16;
    return reinterpret_cast<uintptr_t>(Allocator.Allocate(bytes, Alignment));
  }

  // Allocate data of type T using the per-Assembler allocator.
  template <typename T> T *Allocate() { return Allocator.Allocate<T>(); }

  // Align the tail end of the function to the required target alignment.
  virtual void alignFunction() = 0;

  virtual SizeT getBundleAlignLog2Bytes() const = 0;

  virtual llvm::ArrayRef<uint8_t> getNonExecBundlePadding() const = 0;

  // Mark the current text location as the start of a CFG node
  // (represented by NodeNumber).
  virtual void BindCfgNodeLabel(SizeT NodeNumber) = 0;

  virtual bool fixupIsPCRel(FixupKind Kind) const = 0;

  // Return a view of all the bytes of code for the current function.
  llvm::StringRef getBufferView() const;

  const FixupRefList &fixups() const { return buffer_.fixups(); }

  AssemblerFixup *createFixup(FixupKind Kind, const Constant *Value) {
    return buffer_.createFixup(Kind, Value);
  }

  void emitIASBytes(GlobalContext *Ctx) const;

private:
  ArenaAllocator<32 * 1024> Allocator;

protected:
  AssemblerBuffer buffer_;
};

} // end of namespace Ice

#endif // SUBZERO_SRC_ASSEMBLER_H_