Make the type of this parameter a pointer-to-const warning when declaring a FreeRTOS task

[zazas321]

We use SonarLint to analyze the code. The default way to create a simple FreeRTOS task is as shown below:

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static void HELLO_TASK(void *param)
{
    UNUSED(param);
    for (;;)
    {
        printf("This is normal message1 without ANSI color code \n");
        vTaskDelay(1000 / portTICK_PERIOD_MS);
    }
}

However, sonarlint complains about this and gives us a warning :
Make the type of this parameter a pointer-to-const. The current type of "param" is "void *".

What could be the issue with this and why is it giving a warning? I know its not a big deal but I am just curious to understand.

[mbratch]

FreeRTOS has a macro with casting built in, `pdMS_TO_TICKS`. I use this all the time instead of literally putting the conversion in as `1000/period_in_ms`. So I would write:

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vTaskDelay(pdMS_TO_TICKS(portTICK_PERIOD_MS));

Have you tried that and does it get rid of the warning?
The only caveat is that the macro only works if `configTICK_RATE_HZ` is not greater than 1000.

[MicroController]

Make the type of this parameter a pointer-to-const. The current type of "param" is "void *".

What could be the issue with this and why is it giving a warning? I know its not a big deal but I am just curious to understand.

Not 100% sure about Sonar here, but I assume that Sonar sees that you 1) receive a pointer as argument and 2) never write to the pointer's target. If you never (intend to) write, declaring the parameter 'const <whatever>*' would be cleaner/safer/more explicit and hence better practice, because it expresses that what's pointed to is input and input-only to your function, and might spare hypothetical callers of your function the need to cast away a const modifier.

(I just googled it and, apparently, 'pointee' is a term actually used for "an object a pointer points to"... So please mentally replace 'pointer's target' above by 'pointee' )

[zazas321]

It is still not clear to me how can I avoid this warning.

I have tried to declare my task with const void* param as shown below:

Code: Select all

static void HELLO_TASK(const void *param)
{
    UNUSED(param);
    for (;;)
    {
        printf("This is normal message1 without ANSI color code \n");
        vTaskDelay(1000 / portTICK_PERIOD_MS);
    }
}

This time, I am getting another warning:

Code: Select all

Either add a parameter list or the "&" operator to this use of "HELLO_TASK".

[zazas321]

FreeRTOS has a macro with casting built in, `pdMS_TO_TICKS`. I use this all the time instead of literally putting the conversion in as `1000/period_in_ms`. So I would write:

Code: Select all

vTaskDelay(pdMS_TO_TICKS(portTICK_PERIOD_MS));

Have you tried that and does it get rid of the warning?
The only caveat is that the macro only works if `configTICK_RATE_HZ` is not greater than 1000.

I do not think that the issue is related to vTaskDelay(pdMS_TO_TICKS(portTICK_PERIOD_MS))

I think it is related to task function declaration:

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static void HELLO_TASK(void *param)

[mbratch]

I do not think that the issue is related to vTaskDelay(pdMS_TO_TICKS(portTICK_PERIOD_MS))

I think it is related to task function declaration:

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static void HELLO_TASK(void *param)

You're right! I'm so sorry and misread your original post and missed the detail you noted. My apologies.

Make the type of this parameter a pointer-to-const. The current type of "param" is "void *".

What's the context of this function? Is it just a function, or is it a static member of a class? You are showing the definition of the function, but is there a declaration in a header? How does "UNUSED" expand in this case?

[zazas321]

@mbratch

It is a simple static declaration of a freertos task function in my main.c. The full code is as following (my main.c):

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#include <stdio.h>
#include <inttypes.h>
#include "sdkconfig.h"
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "esp_chip_info.h"
#include "esp_flash.h"
#include "esp_system.h"

#define UNUSED(x) (void)(x) // macro for unused parameters


static void HELLO_TASK(const void *param);

void app_main(void)
{
    printf("Hello world!\n");
    xTaskCreate( HELLO_TASK,  "Hello_task", 2048, NULL, 5, NULL);
    
}


static void HELLO_TASK(const void *param)
{
    UNUSED(param);
    for (;;)
    {
        printf("This is normal message1 without ANSI color code \n");
        vTaskDelay(1000 / portTICK_PERIOD_MS);
    }
}

It is as simple as that. The error will persist if I declare a function in some .c file and declare a prototype in .h file so the fact that this is a static declaration does not have anything to do with it.

How does "UNUSED" expand in this case?

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#define UNUSED(x) (void)(x) // macro for unused parameters

But it should not have anything to do with that warning. I can remove the UNUSED line and still get the same warning

[MicroController]

It is still not clear to me how can I avoid this warning.

What do you mean? You got rid of the warning by using a pointer-to-const, didn't you?

This time, I am getting another warning:

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Either add a parameter list or the "&" operator to this use of "HELLO_TASK".

->

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xTaskCreate( &HELLO_TASK,  "Hello_task", 2048, NULL, 5, NULL);

xTaskCreate expects a function pointer as it's first argument. From the context, i.e. the function name 'HELLO_TASK' appearing without trailing (someParameter), the compiler can deduce that you actually want to refer to the function's address instead of calling HELLO_TASK, but making your intention explicit here is recommended - and may be required by some C standard.

[chegewara]

Those 2 are not the same declarations/definitions and one is not what xTaskCreate expects

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void HELLO_TASK(void *param); // GOOD
vs
void HELLO_TASK(const void *param); // WRONG

and here is error example

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error: invalid conversion from 'void (*)(const void*)' to 'TaskFunction_t' {aka 'void (*)(void*)'} [-fpermissive]

Another thing. It does not matter how you pass function, because function is always passed by address/pointer, its just for convenience
Both are the same and correct

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xTaskCreate( HELLO_TASK,  "Hello_task", 2048, NULL, 5, NULL); // w/o &
vs 
xTaskCreate( &HELLO_TASK,  "Hello_task", 2048, NULL, 5, NULL); // with &

As for the OP, i have no idea about SonarLint, but i found this, which is suggesting the problem is in SonarLint itself (not your code):
https://community.sonarsource.com/t/wro ... st/58181/3

[MicroController]

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error: invalid conversion from 'void (*)(const void*)' to 'TaskFunction_t' {aka 'void (*)(void*)'} [-fpermissive]

You're partially right. Actually, it's a C++ error... In C I get a warning.

Another thing. It does not matter how you pass function, ...

To Sonar it does matter, as it tells us "Either add a parameter list or the "&" operator to this use of "HELLO_TASK"." If you have a better idea, please share.