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Detect Out of Bound Array Access Errors

Design Error Detection for Out of Bound Array Access

Simulink® Design Verifier™ design error detection analysis detects out of bound array access errors in your model. In simulation, when your model attempts to access an array element using an invalid index, an out of bound array access error occurs.

To detect out of bound array access errors in your model:

  1. On the Design Verifier tab, in the Mode section, select Design Error Detection.

  2. Click Error Detection Settings.

  3. In the Configuration Parameters dialog box, in Design Error Detection pane, select Out of bound array access.

  4. Click OK.

  5. Click Detect Design Errors.

    The Simulink Design Verifier log window opens, showing the progress of the analysis.

    When the analysis is complete:

    • The software highlights the model with the analysis results.

    • The Simulink Design Verifier Results dialog box opens and displays an analysis summary.

Note

If a model contains out of bound array access error, after the first occurrence of array access, Simulink Design Verifier assumes that the array index is within bounds for the remaining analysis. Hence, design error detection objectives that are analyzed after this assumption may be reported as valid, even if the design errors occur in the model.

Detect Out of Bound Array Access Example Model

Open Script

This example shows how to detect out of bound array access errors and review the analysis results. In the sldvdemo_array_bounds example model, the ComputeIndex MATLAB Function block uses the input signal values to determine range of indices with minimum minIdx and maximum maxIdx. The ArrayOp_Matlab, ArrayOp_MAL, and ArrayOp_SF blocks use the set of integer indices between minIdx and maxIdx to access array elements and perform array operations.

Step 1: Open the Model

At the command prompt, enter:

open_system('sldvdemo_array_bounds');

Step 2: Perform Design Error Detection Analysis

To perform design error detection analysis, in the Design Verifier tab, click Detect Design Errors. The Simulink® Design Verifier™ Results Summary window opens that displays the progress of the analysis. When the analysis completes, the example model is highlighted with the analysis results.

Step 3: Review Analysis Results

To view the analysis results inside the chart, double-click the ArrayOp_SF Chart block that is highlighted in red.

Simulink Design Verifier detects that the index out of bound errors occurs in array u in state Diff.

Step 4: Create Harness and Simulate Test Cases

Click the first View counterexample link. Simulink Design Verifier creates and opens a harness model that contains test cases, that demonstrate out of bound array access errors. In the Signal Editor dialog box, click Run all to simulate the harness model with Test Case 2.

The simulation stops before entering the state Diff. The Stateflow® Debugger opens. The following error is shown:

Attempted to access index 4 of u with smaller dimension sizes. The valid index range is 0 to 3. This error will stop the simulation. State 'Diff' in Chart 'sldvdemo_array_bounds_harness/Test Unit (copied from sldvdemo_array_bounds)/ArrayOp_SF': y = u[maxIdx] - u[minIdx];

Keep the Stateflow® Debugger open at this breakpoint. In the sldvdemo_array_bounds_harness model, hold your cursor over the Diff state to see the data values at this simulation breakpoint.

Using Test Case 2 input signal values, the ComputeIndex MATLAB Function block determines the range of array indices to be 1:4. One-based indexing is consistent with MATLAB syntax, so these indices are valid for the ArrayOp_Matlab MATLAB Function block and the ArrayOp_MAL Stateflow® chart.

The ArrayOp_SF Stateflow® chart uses C as the action language, which does not support one-based indexing. Thus, 1:4 is not a valid index range for array access in the chart. The valid index range for array access in the chart is 0:3, as reported by the error message. When either maxIdx or minIdx evaluates to 4, an out of bound array access error occurs in the ArrayOp_SF Chart block. For more information on zero-based indexing support, see Differences Between MATLAB and C as Action Language Syntax (Stateflow).

Limitations of Support for Out of Bound Array Access Design Error Detection

Inf Index Values

Design error detection does not support indexing by Inf. If your model attempts to access an array using an index value that evaluates to Inf, design error detection does not report an out of bound array access error, but in simulation, an out of bound array access error occurs.

Index Vector Block with Scalar Data Input

Out of bound array access design error detection does not support Index Vector blocks with scalar data inputs. If your model includes an Index Vector block that specifies a scalar data input instead of a vector data input and the control input causes an out of bounds array access, design error detection does not report an error, but an error occurs in simulation.

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