Stack Guard.

[francisw]

I have a question on stack guard that I tried to enable on nRF52840 and hope you can give me some pointer to verify it is functioning properly.

Basically, I call nrf_stack_guard_init() and compare the behavior of code writing into the stack area. I do not see any difference in behavior. It seems the stack guard was not set up even the function return NRF_SUCCESS.

The stack of my system is at:

0x000000002003c000                __StackLimit = (__StackTop - SIZEOF (.stack_dummy))
0x0000000020040000                PROVIDE (__stack = __StackTop)

 My test code looks like this: 

 

auto* stack_limit_test_address = (uint8_t*) 0x2003c000;
    *stack_limit_test_address = 0;
    stack_limit_test_address = (uint8_t*) 0x2003c001;
    *stack_limit_test_address = 0;
    stack_limit_test_address = (uint8_t*) 0x2003d000;
    *stack_limit_test_address = 1;
    stack_limit_test_address = (uint8_t*) 0x2003e000;
    *stack_limit_test_address = 2;
    stack_limit_test_address = (uint8_t*) 0x2003f000;
    *stack_limit_test_address = 3;
    stack_limit_test_address = (uint8_t*) 0x2003ff00;
    *stack_limit_test_address = 4;
    stack_limit_test_address = (uint8_t*) 0x2003fff0;
    *stack_limit_test_address = 5;
    stack_limit_test_address = (uint8_t*) 0x2003ff00;
    *stack_limit_test_address = 6;
    stack_limit_test_address = (uint8_t*) 0x2003ffff;
    *stack_limit_test_address = 7;
    //stack_limit_test_address = (uint8_t*) 0x20040000;
    //*stack_limit_test_address = 8;                    // Next instruction after this line is executed triggers reset
    //stack_limit_test_address = (uint8_t*) 0x2003f000; // System reset when this line is enabled and executed.
    //*stack_limit_test_address = 9;

    nrf_stack_guard_init();

    stack_limit_test_address = (uint8_t*) 0x2003c000;
    *stack_limit_test_address = 0;
    stack_limit_test_address = (uint8_t*) 0x2003c001;
    *stack_limit_test_address = 0;
    stack_limit_test_address = (uint8_t*) 0x2003d000;
    *stack_limit_test_address = 1;
    stack_limit_test_address = (uint8_t*) 0x2003e000;
    *stack_limit_test_address = 2;
    stack_limit_test_address = (uint8_t*) 0x2003f000;
    *stack_limit_test_address = 3;
    stack_limit_test_address = (uint8_t*) 0x2003ff00;
    *stack_limit_test_address = 4;
    stack_limit_test_address = (uint8_t*) 0x2003fff0;
    *stack_limit_test_address = 5;
    stack_limit_test_address = (uint8_t*) 0x2003ff00;
    *stack_limit_test_address = 6;
    stack_limit_test_address = (uint8_t*) 0x2003ffff;
    *stack_limit_test_address = 7;
    //stack_limit_test_address = (uint8_t*) 0x20040000; // Same behavior as in the case before nrf_stack_guard_init() is called
    //*stack_limit_test_address = 8;                    // Instruction followed this line triggers a reset
    stack_limit_test_address = (uint8_t*) 0x2003f000;
    *stack_limit_test_address = 9;

My stack guard size should have been 128 bytes since NRF_STACK_GUARD_CONFIG_SIZE is kept at default value of 7.

NRF_STACK_GUARD_ENABLED is 1 ( enabled ).

Any idea what I am doing wrong? Am I missing some steps?

[awneil]

[Vidar Berg]

Hi,

Please try to use it with the MPU library like we do in the \peripheral\cli example. The stack guard libary relies on the MPU but assumes it will be enabled by other parts of the program.

Stack guard init from CLI example:

static inline void stack_guard_init(void)
{
    APP_ERROR_CHECK(nrf_mpu_lib_init());
    APP_ERROR_CHECK(nrf_stack_guard_init());
}