Stack overflow detection (method 1 and 2) in FreeRTOS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this FreeRTOS stack overflow hook example (Method 1)?

Consider this FreeRTOS code snippet using stack overflow detection Method 1. What will be the output when a stack overflow is detected?

FreeRTOS

void vApplicationStackOverflowHook(TaskHandle_t xTask, char *pcTaskName) {
    printf("Stack overflow detected in task: %s\n", pcTaskName);
    for(;;); // Infinite loop to halt system
}

// Assume a task named "TaskA" causes stack overflow triggering this hook.

A Prints "Stack overflow detected in task: TaskA" and halts execution in infinite loop

B Prints "Stack overflow detected" without task name and continues running

C System resets immediately without any print output

D No output; the hook is not called automatically

💡 Hint

Method 1 uses a hook function called automatically on stack overflow with task name info.

Method 1 defines vApplicationStackOverflowHook which FreeRTOS calls on stack overflow, passing the task handle and name. The example prints the task name and then halts in an infinite loop.

❓ Predict Output

intermediate

What happens when stack overflow detection Method 2 is enabled and overflow occurs?

Given FreeRTOS configured with stack overflow detection Method 2, what is the expected behavior when a task overflows its stack?

FreeRTOS

#define configCHECK_FOR_STACK_OVERFLOW 2

void vApplicationStackOverflowHook(TaskHandle_t xTask, char *pcTaskName) {
    printf("Overflow detected in %s\n", pcTaskName);
    taskDISABLE_INTERRUPTS();
    for(;;); // Halt
}

// Assume "TaskB" causes overflow.

A The hook prints "Overflow detected in TaskB" and halts system

B The system ignores overflow and continues running

C The hook is not called because Method 2 disables it

D The system resets without any print

💡 Hint

Method 2 checks stack overflow on each context switch and calls the hook.

Method 2 performs a check on each context switch and calls vApplicationStackOverflowHook if overflow is detected, printing the task name and halting.

🧠 Conceptual

advanced

Why does Method 2 stack overflow detection have higher CPU overhead than Method 1?

Choose the best explanation for why FreeRTOS stack overflow detection Method 2 causes more CPU overhead than Method 1.

A Method 2 disables interrupts causing delays in task switching

B Method 2 requires manual calls in each task increasing code size

C Method 2 uses hardware breakpoints which slow down CPU

D Method 2 checks the stack pointer and limits on every context switch, adding extra instructions each time

💡 Hint

Think about when the overflow check happens in each method.

Method 2 performs stack overflow checks on every context switch by inspecting stack pointers, which adds CPU cycles each time a task switch occurs, increasing overhead compared to Method 1.

❓ Predict Output

advanced

What error occurs if configCHECK_FOR_STACK_OVERFLOW is set to 1 but vApplicationStackOverflowHook is missing?

Given FreeRTOS with configCHECK_FOR_STACK_OVERFLOW = 1 but no vApplicationStackOverflowHook defined, what happens when a stack overflow occurs?

A System resets automatically without hook

B Stack overflow detected but no hook called, system continues silently

C Linker error due to missing hook function

D Runtime crash with undefined reference error

💡 Hint

Check if the hook function is required by the FreeRTOS config.

When configCHECK_FOR_STACK_OVERFLOW is 1 or 2, FreeRTOS expects vApplicationStackOverflowHook to be defined. If missing, the linker fails with an undefined reference error.

🔧 Debug

expert

Identify the cause of incorrect stack overflow detection in this Method 1 implementation

Review this Method 1 stack overflow hook code. Why might the stack overflow not be detected correctly?

FreeRTOS

void vApplicationStackOverflowHook(TaskHandle_t xTask, char *pcTaskName) {
    // Incorrectly uses pcTaskName pointer without checking
    if(pcTaskName != NULL) {
        printf("Overflow in task: %s\n", pcTaskName);
    } else {
        printf("Overflow detected but task name missing\n");
    }
}

// Stack overflow occurs but pcTaskName is NULL.

A The stack overflow detection is correct; pcTaskName can be NULL in Method 1

B pcTaskName is NULL because the FreeRTOS config does not store task names, causing incorrect detection

C The hook is not called because configCHECK_FOR_STACK_OVERFLOW is set to 0

D The hook causes a crash because it dereferences a NULL pointer without handling

💡 Hint

Consider how task names are configured and passed to the hook.

If task names are not enabled in FreeRTOS config (configUSE_TRACE_FACILITY or configMAX_TASK_NAME_LEN is zero), pcTaskName may be NULL, so the hook cannot print the name, causing confusion about detection.