trap.h

/*
 * Copyright 2020 Andrei Pangin
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef _TRAP_H
#define _TRAP_H

#include "arch.h"
#include <stdint.h>

const int TRAP_COUNT = 4;

class Trap {
private:
  int _id;
  bool _unprotect;
  bool _protect;
  uintptr_t _entry;
  instruction_t _breakpoint_insn;
  instruction_t _saved_insn;

  bool patch(instruction_t insn);

  static uintptr_t _page_start[TRAP_COUNT];

public:
  explicit Trap(int id)
      : _id(id), _unprotect(true), _protect(WX_MEMORY), _entry(0),
        _breakpoint_insn(BREAKPOINT), _saved_insn(0) {}

  uintptr_t entry() { return _entry; }

  bool covers(uintptr_t pc) {
    // PC points either to BREAKPOINT instruction or to the next one
    return pc - _entry <= sizeof(instruction_t);
  }

  void assign(const void *address, uintptr_t offset = BREAKPOINT_OFFSET);
  void pair(Trap &second);

  bool install() { return _entry == 0 || patch(_breakpoint_insn); }

  bool uninstall() { return _entry == 0 || patch(_saved_insn); }

  static bool isFaultInstruction(uintptr_t pc);
};

#endif // _TRAP_H