[amiga386]

That line allocates nothing. The function is their version of explicit_bzero(). The line casts an existing pointer passed in (e.g. pointing to something on the stack, or allocated by you) to a volatile pointer, which prevents the compiler from optimising away the writes.

Their README states "zero dynamic allocation: all operations use caller-provided buffers" and "Full COSE lifecycle in ~<1KB RAM (excluding wolfCrypt internals)", so I assume their stack usage is low too, because you (the caller) will own and have to allocate all buffers yourself

[Neywiny]

p is allocated on the stack

[amiga386]

So what? So is every automatic variable, including size_t i on the next line, unless it fits in a register. So are the platform-specific preserved registers across function calls, so are the function parameters if the platform declares they need to be on the stack, so is the return value in some cases. So is the preserved return address / link register for the function call.

Nobody is going to write code with exclusively global variables and GOTO instead of function calls, in order to use zero stack. And if they did, the other claim (no .data or .bss) would be untrue.

I'm not sure how you misinterpreted "Zero dynamic allocation" to mean "not even stack variables", because nobody would read it that way, and I don't think anyone sane would use software that promised it used no stack.