I'm developing something in an embedded context with Zephyr.
Essentially I'm dealing with a boot-loop caused by a stack overflow. The stack overflow goes away when I change an unused parameter of a function call deep inside my main. To make sure that the problem is not with the inside of the function, I hard-coded its implementation to be return 0;.
The offending line being like such creates a boot loop:
uint8_t port;
ret = foo(&port, NULL, NULL);
But the line missing the de-referenced port has the code run normally:
uint8_t port;
ret = foo(NULL, NULL, NULL);
Mind you, as I've already said, the implementation of foo is hard-coded to return 0. The parameters are at no point used. Furthermore, I'm sure the line is never actually reached at runtime (in this case) as it lives behind some conditionals requiring my interaction to actually go through.
I've started to give up and blame things on faulty memory or ESD damage but when I tried the same code with the same changes on a spare piece of hardware I had laying around the same thing happens. What is it that I'm missing? I genuinely don't know what else I could do to find out why this is happening and how to fix it. I don't have an access to a debugger for this microcontroller (SAMD21) so I'm at a bit of a loss... Any ideas (or at least sympathy)?
Nevermind, I've found the culprit - a simple stack overflow. I was one byte away from it before the addition of the uint8_t port variable declaration into main. The variable when not used as a parameter in foo() was being optimised away by the compiler. Having one fewer byte on the call stack apparently was enough to prevent the overflow.
Solution: increase stack size and be more careful with clogging it up with unnecessary items.