Stack overflow detection (method 1 and 2) in FreeRTOS - Mini Project: Build & Apply

Stack overflow detection (method 1 and 2)

📖 Scenario: You are working on an embedded system using FreeRTOS. You want to protect your tasks from crashing due to stack overflow errors. FreeRTOS offers two methods to detect stack overflow. You will write code to enable and test both methods.

🎯 Goal: Enable stack overflow detection methods 1 and 2 in FreeRTOS and write a simple task that triggers the detection. You will configure the FreeRTOS settings, implement the overflow hook functions, and observe the detection in action.

📋 What You'll Learn

Create a FreeRTOS task with a small stack size

Enable stack overflow detection method 1

Enable stack overflow detection method 2

Implement the stack overflow hook functions

Trigger a stack overflow to test detection

Print a message when overflow is detected

💡 Why This Matters

🌍 Real World

Embedded systems often run multiple tasks with limited memory. Detecting stack overflow prevents crashes and hard-to-debug errors.

💼 Career

Embedded software engineers must ensure system reliability by using RTOS features like stack overflow detection to catch bugs early.

1

Create a FreeRTOS task with a small stack size

Write code to create a FreeRTOS task called vOverflowTask with a stack size of configMINIMAL_STACK_SIZE and priority 1. Use the function xTaskCreate() and include the task function prototype void vOverflowTask(void *pvParameters);.

FreeRTOS

# Create the task vOverflowTask with stack size configMINIMAL_STACK_SIZE and priority 1
// Your code here

Hint

Use xTaskCreate() with the task function name, a name string, stack size, parameters as NULL, priority 1, and no task handle.

2

Enable stack overflow detection method 1

Add the FreeRTOS configuration line #define configCHECK_FOR_STACK_OVERFLOW 1 before including FreeRTOS headers. This enables stack overflow detection method 1.

FreeRTOS

#define configCHECK_FOR_STACK_OVERFLOW 1
// Your code here
#include "FreeRTOS.h"
#include "task.h"

void vOverflowTask(void *pvParameters);

int main(void) {
    xTaskCreate(vOverflowTask, "OverflowTask", configMINIMAL_STACK_SIZE, NULL, 1, NULL);
    vTaskStartScheduler();
    for(;;);
}

void vOverflowTask(void *pvParameters) {
    for(;;) {
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

Hint

Place the #define before including FreeRTOS headers to enable method 1.

3

Implement the stack overflow hook function for method 1

Write the function void vApplicationStackOverflowHook(TaskHandle_t xTask, char *pcTaskName) that prints "Stack overflow detected in task: " followed by the task name pcTaskName. Use printf().

FreeRTOS

#define configCHECK_FOR_STACK_OVERFLOW 1
#include "FreeRTOS.h"
#include "task.h"

void vOverflowTask(void *pvParameters);

void vApplicationStackOverflowHook(TaskHandle_t xTask, char *pcTaskName) {
    // Your code here
}

int main(void) {
    xTaskCreate(vOverflowTask, "OverflowTask", configMINIMAL_STACK_SIZE, NULL, 1, NULL);
    vTaskStartScheduler();
    for(;;);
}

void vOverflowTask(void *pvParameters) {
    for(;;) {
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

Hint

Implement the hook function exactly with the given signature and use printf to show the task name.

4

Enable stack overflow detection method 2 and trigger overflow

Add #define configCHECK_FOR_STACK_OVERFLOW 2 to enable method 2 instead of method 1. Modify vOverflowTask to declare a local array char buffer[10] and write beyond its bounds in a loop to cause stack overflow. Print "Stack overflow detected in task: " with the task name in vApplicationStackOverflowHook. Run the program to see the detection message.

FreeRTOS

#define configCHECK_FOR_STACK_OVERFLOW 2

void vOverflowTask(void *pvParameters) {
    // Your code here to cause stack overflow
}

Hint

Change the config macro to 2 and write beyond the buffer size inside the task to trigger overflow detection.

Practice

1. What is the main purpose of stack overflow detection in FreeRTOS?

easy

A. To reduce RAM usage by tasks

B. To prevent tasks from using more stack memory than allocated

C. To increase CPU clock speed

D. To speed up task switching

Solution

1. Step 1: Understand stack overflow concept

   Stack overflow happens when a task uses more stack memory than allocated, causing memory corruption.

2. Step 2: Identify purpose of detection

   Stack overflow detection helps catch this problem early to prevent crashes or unpredictable behavior.

3. Final Answer:

   To prevent tasks from using more stack memory than allocated -> Option B

4. Quick Check:

   Stack overflow detection = prevent excess stack use [OK]

Hint: Stack overflow detection stops tasks using too much stack [OK]

Common Mistakes:

• Confusing stack overflow with CPU speed
• Thinking it reduces RAM usage
• Assuming it speeds up task switching

2. Which FreeRTOS configuration enables Method 1 stack overflow detection?

easy

A. configMAX_PRIORITIES set to 5

B. configUSE_PREEMPTION set to 0

C. configUSE_IDLE_HOOK set to 1

D. configCHECK_FOR_STACK_OVERFLOW set to 1 or 2

Solution

1. Step 1: Identify config for stack overflow detection

   FreeRTOS uses configCHECK_FOR_STACK_OVERFLOW to enable Method 1 detection.

2. Step 2: Understand valid values

   Setting configCHECK_FOR_STACK_OVERFLOW to 1 or 2 activates automatic detection on context switches.

3. Final Answer:

   configCHECK_FOR_STACK_OVERFLOW set to 1 or 2 -> Option D

4. Quick Check:

   configCHECK_FOR_STACK_OVERFLOW = 1 or 2 [OK]

Hint: Method 1 uses configCHECK_FOR_STACK_OVERFLOW = 1 or 2 [OK]

Common Mistakes:

• Confusing unrelated config options
• Using configUSE_PREEMPTION for stack checks
• Setting configMAX_PRIORITIES thinking it affects stack

3. Given this FreeRTOS hook function for Method 1:

void vApplicationStackOverflowHook(TaskHandle_t xTask, char *pcTaskName) {
    printf("Stack overflow detected in task: %s\n", pcTaskName);
    while(1); // Halt
}

What will happen if a stack overflow is detected?

medium

A. Prints task name and halts the system

B. Resets the task automatically

C. Ignores the overflow and continues

D. Logs overflow but continues running

Solution

1. Step 1: Analyze the hook function code

   The function prints the task name where overflow occurred and then enters an infinite loop.

2. Step 2: Understand effect of infinite loop

   The infinite loop halts the system to prevent further damage after overflow detection.

3. Final Answer:

   Prints task name and halts the system -> Option A

4. Quick Check:

   Stack overflow hook prints and halts [OK]

Hint: Stack overflow hook prints and stops system [OK]

Common Mistakes:

• Thinking system resets automatically
• Assuming overflow is ignored
• Believing task restarts without halt

4. In Method 2 stack overflow detection, which mistake will cause incorrect detection?

medium

A. Using vApplicationStackOverflowHook function

B. Enabling configCHECK_FOR_STACK_OVERFLOW to 2

C. Not initializing the stack pointer check value properly

D. Setting configUSE_PREEMPTION to 1

Solution

1. Step 1: Understand Method 2 detection

   Method 2 manually checks stack pointer against a known value to detect overflow.

2. Step 2: Identify common error

   If the initial stack pointer check value is not set correctly, the comparison will be invalid, causing false negatives or positives.

3. Final Answer:

   Not initializing the stack pointer check value properly -> Option C

4. Quick Check:

   Method 2 needs correct stack pointer init [OK]

Hint: Method 2 needs proper stack pointer initialization [OK]

Common Mistakes:

• Confusing Method 1 config with Method 2
• Ignoring stack pointer initialization
• Assuming hook function is used in Method 2

5. You want to implement stack overflow detection in your FreeRTOS project using Method 1. Which steps should you follow to ensure it works correctly?

hard

A. Set configCHECK_FOR_STACK_OVERFLOW to 1 or 2 and implement vApplicationStackOverflowHook

B. Manually compare stack pointers in each task without config changes

C. Disable preemption and use configUSE_IDLE_HOOK for detection

D. Increase task stack size to avoid overflow without detection

Solution

1. Step 1: Enable Method 1 detection in config

   Set configCHECK_FOR_STACK_OVERFLOW to 1 or 2 to activate automatic detection during context switches.

2. Step 2: Implement the hook function

   Define vApplicationStackOverflowHook to handle overflow events, e.g., log and halt.

3. Final Answer:

   Set configCHECK_FOR_STACK_OVERFLOW to 1 or 2 and implement vApplicationStackOverflowHook -> Option A

4. Quick Check:

   Method 1 = config + hook function [OK]

Hint: Method 1 needs config and hook function implemented [OK]

Common Mistakes:

• Trying manual pointer checks for Method 1
• Disabling preemption thinking it helps detection
• Ignoring hook function implementation