debugserver arm64 single-step state

void DNBArchMachARM64::ThreadWillResume() {
  // Do we need to step this thread? If so, let the mach thread tell us so.
  if (m_thread->IsStepping()) {
    EnableHardwareSingleStep(true);
  }

  // Disable the triggered watchpoint temporarily before we resume.
  // Plus, we try to enable hardware single step to execute past the instruction
  // which triggered our watchpoint.
  if (m_watchpoint_did_occur) {
    if (m_watchpoint_hw_index >= 0) {
      kern_return_t kret = GetDBGState(false);
      if (kret == KERN_SUCCESS &&
          !IsWatchpointEnabled(m_state.dbg, m_watchpoint_hw_index)) {
        // The watchpoint might have been disabled by the user.  We don't need
        // to do anything at all
        // to enable hardware single stepping.
        m_watchpoint_did_occur = false;
        m_watchpoint_hw_index = -1;
        return;
      }

      DisableHardwareWatchpoint(m_watchpoint_hw_index, false);
      DNBLogThreadedIf(LOG_WATCHPOINTS,
                       "DNBArchMachARM64::ThreadWillResume() "
                       "DisableHardwareWatchpoint(%d) called",
                       m_watchpoint_hw_index);

      // Enable hardware single step to move past the watchpoint-triggering
      // instruction.
… more in source

bool DNBArchMachARM64::ThreadDidStop() {
  bool success = true;

  m_state.InvalidateAllRegisterStates();

  if (m_watchpoint_resume_single_step_enabled) {
    // Great!  We now disable the hardware single step as well as re-enable the
    // hardware watchpoint.
    // See also ThreadWillResume().
    if (EnableHardwareSingleStep(false) == KERN_SUCCESS) {
      if (m_watchpoint_did_occur && m_watchpoint_hw_index >= 0) {
        ReenableHardwareWatchpoint(m_watchpoint_hw_index);
        m_watchpoint_resume_single_step_enabled = false;
        m_watchpoint_did_occur = false;
        m_watchpoint_hw_index = -1;
      } else {
        DNBLogError("internal error detected: m_watchpoint_resume_step_enabled "
                    "is true but (m_watchpoint_did_occur && "
                    "m_watchpoint_hw_index >= 0) does not hold!");
      }
    } else {
      DNBLogError("internal error detected: m_watchpoint_resume_step_enabled "
                  "is true but unable to disable single step!");
    }
  }

  // Are we stepping a single instruction?
  if (GetGPRState(true) == KERN_SUCCESS) {
    // We are single stepping, was this the primary thread?
    if (m_thread->IsStepping()) {
… more in source

kern_return_t DNBArchMachARM64::EnableHardwareSingleStep(bool enable) {
  DNBError err;
  DNBLogThreadedIf(LOG_STEP, "%s( enable = %d )", __FUNCTION__, enable);

  err = GetGPRState(false);

  if (err.Fail()) {
    err.LogThreaded("%s: failed to read the GPR registers", __FUNCTION__);
    return err.Status();
  }

  err = GetDBGState(false);

  if (err.Fail()) {
    err.LogThreaded("%s: failed to read the DBG registers", __FUNCTION__);
    return err.Status();
  }

#if defined(DEBUGSERVER_IS_ARM64E)
  uint64_t pc = DNBFixAddress(
      reinterpret_cast<uint64_t>(m_state.context.gpr.__opaque_pc));
#else
  uint64_t pc = m_state.context.gpr.__pc;
#endif

  if (enable) {
    DNBLogThreadedIf(LOG_STEP,
                     "%s: Setting MDSCR_EL1 Single Step bit at pc 0x%llx",
                     __FUNCTION__, pc);
    m_state.dbg.__mdscr_el1 |= SS_ENABLE;
… more in source