text: /*
   * Copyright (c) 2020, the SerenityOS developers.
   *
   * SPDX-License-Identifier: BSD-2-Clause
   */
  
  #include <AK/Atomic.h>
  #include <AK/Optional.h>
  #include <AK/Types.h>
  
  #pragma once
  
  namespace Kernel {
  
  struct RegisterState;
  
  [[nodiscard]] bool safe_memcpy(void* dest_ptr, const void* src_ptr, size_t n, void*& fault_at) __attribute__((used));
  [[nodiscard]] ssize_t safe_strnlen(const char* str, size_t max_n, void*& fault_at) __attribute__((used));
  [[nodiscard]] bool safe_memset(void* dest_ptr, int c, size_t n, void*& fault_at) __attribute__((used));
  [[nodiscard]] Optional<u32> safe_atomic_fetch_add_relaxed(volatile u32* var, u32 val) __attribute__((used));
  [[nodiscard]] Optional<u32> safe_atomic_exchange_relaxed(volatile u32* var, u32 val) __attribute__((used));
  [[nodiscard]] Optional<u32> safe_atomic_load_relaxed(volatile u32* var) __attribute__((used));
  [[nodiscard]] bool safe_atomic_store_relaxed(volatile u32* var, u32 val) __attribute__((used));
  [[nodiscard]] Optional<bool> safe_atomic_compare_exchange_relaxed(volatile u32* var, u32& expected, u32 val) __attribute__((used));
  
  [[nodiscard]] ALWAYS_INLINE Optional<u32> safe_atomic_fetch_and_relaxed(volatile u32* var, u32 val)
  {
      auto expected_value = safe_atomic_load_relaxed(var);
      if (!expected_value.has_value())
          return {}; // fault
      u32& expected = expected_value.value();
      for (;;) {
          auto result = safe_atomic_compare_exchange_relaxed(var, expected, expected & val);
          if (!result.has_value())
              return {}; // fault
          if (result.value())
              return expected; // exchanged
  
          // This is only so that we don't saturate the bus...
          AK::atomic_thread_fence(AK::MemoryOrder::memory_order_acquire);
      }
  }
  
  [[nodiscard]] ALWAYS_INLINE Optional<u32> safe_atomic_fetch_and_not_relaxed(volatile u32* var, u32 val)
  {
      auto expected_value = safe_atomic_load_relaxed(var);
      if (!expected_value.has_value())
          return {}; // fault
      u32& expected = expected_value.value();
      for (;;) {
          auto result = safe_atomic_compare_exchange_relaxed(var, expected, expected & ~val);
          if (!result.has_value())
              return {}; // fault
          if (result.value())
              return expected; // exchanged
  
          // This is only so that we don't saturate the bus...
          AK::atomic_thread_fence(AK::MemoryOrder::memory_order_acquire);
      }
  }
  
  [[nodiscard]] ALWAYS_INLINE Optional<u32> safe_atomic_fetch_or_relaxed(volatile u32* var, u32 val)
  {
      auto expected_value = safe_atomic_load_relaxed(var);
      if (!expected_value.has_value())
          return {}; // fault
      u32& expected = expected_value.value();
      for (;;) {
          auto result = safe_atomic_compare_exchange_relaxed(var, expected, expected | val);
          if (!result.has_value())
              return {}; // fault
          if (result.value())
              return expected; // exchanged
  
          // This is only so that we don't saturate the bus...
          AK::atomic_thread_fence(AK::MemoryOrder::memory_order_acquire);
      }
  }
  
  [[nodiscard]] ALWAYS_INLINE Optional<u32> safe_atomic_fetch_xor_relaxed(volatile u32* var, u32 val)
  {
      auto expected_value = safe_atomic_load_relaxed(var);
      if (!expected_value.has_value())
          return {}; // fault
      u32& expected = expected_value.value();
      for (;;) {
          auto result = safe_atomic_compare_exchange_relaxed(var, expected, expected ^ val);
          if (!result.has_value())
              return {}; // fault
          if (result.value())
              return expected; // exchanged
  
          // This is only so that we don't saturate the bus...
          AK::atomic_thread_fence(AK::MemoryOrder::memory_order_acquire);
      }
  }
  
  bool handle_safe_access_fault(RegisterState& regs, u32 fault_address);
  
  }
  