Approximated stack overflow detection via stack canaries about probe-run

[japaric]

even while it still runs

I would be against this particular variant. Polling a second memory block can easily halve the throughput of the log stream data and probe-rs's RTT implementation is already rather slow.

It is currently unclear how this interacts with program that use the heap.

I don't think there are strong guidelines but either a chunk of .bss memory will be used as the heap or the .heap section defined in cortex-m-rt will be sized accordingly and the whole section will be passed to the memory allocator.

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Related feature: optionally we can "paint" all the potential stack memory with a known pattern and once the program has finished we look for the "watermark" level and report the max stack usage for this particular program run.

[jonas-schievink]

It seems that c-m-rt places the heap start symbol __sheap right after .uninit in RAM, but not inside any section:

https://github.com/rust-embedded/cortex-m-rt/blob/3ce46b3c19158cb9be4f9d2a3c00d5723e62ded5/link.x.in#L139-L141

That means there's no section we can use to detect presence of a heap. Can we detect whether the symbol was referenced by looking for it in the ELF file or will it always be there?

[jonas-schievink]

I guess for compatibility with other runtimes we could look for any symbol that points to the first address after .uninit. There shouldn't be any reason to refer to that address unless you use a heap.

[jonas-schievink]

Looks like __sheap is always present even when it's not used by anything :/