RM46L852: VLA and malloc - How to use the stack properly

Hello Gabriel,

We have looped in associated experts, please allow some time for review and associated feedback. Thank you.

Best Regards,

Zackary Fleenor

Thanks Fleenor.

Hi!
Any update on this?
This is critical for safety certification.

Hi Gabriel,

Gabriel B said:

I'm I correct that VLA actually does not use the stack? 

The variables allocated by malloc() are stored in heap memory instead of stack.

I don't know VLA RTOS. In freeRTOS, it is better to use the freeRTOS version of malloc and free: pvPortMalloc() and vPortFree().

Hi QJ, 

Thanks for your answer.

To my understanding, VLAs are part of the C runtime
Therefore, it's a TI implementation question, not FreeRTOS.

To be clear, we are not using FreeRTOS heap.

 

Hi Gabriel,

Thanks Gabriel. I got it that the VLA stands for "variable length arrays". The VLA is supported in the TI ARM compiler. As you said, the variable length array is allocated memory by calling malloc. So, you need to be sure to have enough heap memory allocated for using VLA. 

Gabriel B said:

Are VLAs guaranty to free the memory properly?
Are VLAs RTOS safe?
Is there a way to use those safely? 
Is there an alloca function in the std library?

I don't know the answer to those questions. Could you please post those questions to TI CCS/Compiler forum? Thanks

Here's a link to my new thread.

https://e2e.ti.com/support/microcontrollers/arm-based-microcontrollers-group/arm-based-microcontrollers/f/arm-based-microcontrollers-forum/1205940/rm46l852-vla-and-malloc---how-to-use-the-stack-properly

I will complete this one