Clarify that the stack is only 4K

[Skepfyr]

I was getting the completely inscrutable error message firmware crashed: out-of-bounds store on 0x000fd2b0+4. After a lot of debugging, involving stepping through your RISCV interpreter (nice job BTW), I realised that it was a stack overrun and looked in the linker script to see that the stack is only 4K.

This took a bunch of time and I suspect is not something that people using kartoffel are able or want to do, it would be useful to document that the stack is only 4K and potentially provide better error messages or debug tooling.

[Patryk27]

Hah, nice one on reaching the limit - thought 4kb ought to be enough for anybody™

I should be able to provide a dedicated error message for this, let me play around.

[Skepfyr]

I threw all of my state on the stack as it's the easiest allocator! I'm now refactoring it to put the data in statics which will bring my stack usage waayy down. (Although statics are an absolute pain to use).

[Patryk27]

fwiw, you can just use the alloc crate - i.e. Box::new(), Vec::new() etc. work out of the box.

[Skepfyr]

Ooooooooh lol, I should have tried that before assuming there wouldn't be an allocator.

[Patryk27]

😄

It's provided as a convenience and automatically allocated utilizing rest of the RAM, i.e. whatever's remaining after the code:

• kartoffels/app/crates/kartoffel/kartoffel.ld

  Line 25 in 4f5dcba

  _heap_start = .;

• kartoffels/app/crates/kartoffel/src/allocator.rs

  Line 15 in 4f5dcba

  static ALLOCATOR: Talck<Mutex<()>, ClaimOnOom> = unsafe {