Removing heap allocation using linkscripts

[eaad]

Hello,

In the project im involved in, we're using nxp product that runs FreeRTOS as os. As our application does not allocate dynamic memory using the ordinary mallocs, I want to remove the heap allocation that the linker puts in the binary.

The method for this is to put the relevant ldt file in the linkscripts folder, which I did- specifically by overriding the heap size to be zero. this works.

How ever, it will be better for me if I could just discard the symbol of the heap from the binary (heap_symbol which is set to _pvHeapStart) because otherwise this symbol gets its address, and it is possible to override memory using its address. My problem is that when im just discarding it I get references errors of gcc files (_cr_sbrk.c) expecting this reference.

I would like to ask for a help reaching my goal which is safely remove the heap allocation from the linker.

Thanks

[eaad · Accepted solution]

I just want to update that I found a good enough solution, based on this post: https://stackoverflow.com/questions/40130374/gcc-how-to-disable-heap-usage-entirely-on-an-mcu

(idea is to redirect dynamic memory allocation methods to unimplemented method, which leads to linker errors if one uses them)

[ErichStyger]

Hi @eaad ,

In case you want use FreeMarker Scripts or in general check if malloc() is still used, maybe this helps: https://mcuoneclipse.com/2022/11/06/how-to-make-sure-no-dynamic-memory-is-used/

Erich

[eaad]

Hi @ErichStyger, thank you. Actually i was trying the approach of removing the definition of the heap using the FreeMarker Scripts, but I was not able to overcome the __sbrk function error that comes on the linking stage, And even though the map gives me the list, what is a way to overcome that issue?

i get a libc reference:

/usr/local/mcuxpressoide-11.5.1_7266/ide/plugins/com.nxp.mcuxpresso.tools.linux_11.5.1.202201181444/tools/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+dp/hard/libcr_c.a(alloc.o)
max_utilize_stack.lto_priv.0

what do you think? i couldn't figure that from the article. btw, as you said there, i prefer removing the definition in addition to redirecting the malloc/free ops.



ty,

Efraim

[ErichStyger]

If __sbrk is still referenced, it means that your application is still possibly calling malloc() or any other dynamic memory allocator.

I suggest you link with the heap in the linker script enabled and then use the Image Info to find out who is calling/using malloc and sbrk. Most likely it is a printf() somewhere in your code?

[eaad]

Yea, I will re do that, and update about my findings