Determine heap free space on STM32

[tinkerer42]

I'm using an STM32L4 with STM32CubeIDE, bare metal, and using C++ along with Cube's C libraries. The compiler is the GCC/G++ supplied with STM32CubeIDE.

I have some dynamic memory usage in STL containers etc. I'm aware of the recommendation not to use dynamic memory on bare-metal embedded systems, but it is generally used only during initialization, minimizing the complications.

I would like to know how much of the heap I'm using, and found no way to do that. I saw discussions of __heapstats but it doesn't seem to be defined in this toolchain (?).

It doesn't have to be a programmatic way, if there is some internal data structure of newlib or whatever that I can watch while debugging that will suffice.

p.s.

I know the term "free heap space" is not very well defined, because of block sizes and fragmentation, but I suspect that in my case it's going to be one big free block.

any ideas?

[Tesla DeLorean]

Walk the linked list the allocator uses..

[tinkerer42]

thanks, not pretty but I'll do it if there's no built-in lib to do it for me. I'd like to ask then -

• what's the name of the data structure?
• Is it the same structure both for C's malloc() and C++'s new() (or equivalent operations)?

the compiler is the GCC / G++ supplied with STM32CubeIDE, by the way.

[Tesla DeLorean]

The question looks more expansive now.

I'm using Keil.

__microlib_freelist_initialised

__microlib_freelist

The structure is ahead of the pointer returned by malloc()

[tinkerer42]

Thanks, can anyone provide a similar answer for STM32CubeIDE's toolchain?

[Tesla DeLorean]

I'd have thought you could objcopy or fromelf the symbol and disassembly/listing of the code.

https://community.st.com/s/question/0D53W00000e0zTdSAI/malloc1

https://sourceware.org/git/?p=newlib-cygwin.git;a=blob;f=newlib/libc/stdlib/mallocr.c;h=ecc445f3d36365a4840e31c737db5018ddba42e9;hb=fffd2770db9aa7aa0404d124d8ce4bf00f7f4c71

https://code.woboq.org/userspace/glibc/malloc/malloc.c.html

[S.Ma]

Why not union your variables with main global ones if they are exclusied in sequence, saving mallocs logic? (Manual clearing.maybe needed)

[Tesla DeLorean]

Dynamic allocation has its place, especially allocating buffers and objects at start-up, and where the usage might be configurable, or transitory

Now obviously using it like you would on a desktop, with no regard to leaks, or balance, that's a problem. Using it continuously is also not particularly advisable.

Then again using globals in an excessive and sloppy manner is also something to be avoided.

[tinkerer42]

the short answer is that it leads me to cleaner code: using STL containers and other C++ features. The longer answer is that it has advantages and disadvantages, it is a common heated arguing point in the embedded community. I would really prefer NOT to open this discussion here, as it would completely distract from my original question.

So: does anyone know how to check heap free space when using the STM32CubeIDE toolchain?

[tinkerer42]

What would I do with looking at the ELF etc? as they are the results of compilation and therefore know nothing about the runtime state of the heap?