I am currently creating a XDP program where I have a bunch of function calls and, as such, the stack gets fuller as the program is executed.
However, I am confused as to how the stack size is measured. For example, lets say that I call the following function:

function_test(&value_a);

And value_a is the address of an instance of the following structure: (I’m skipping value5 to value99)

struct struct_test {
   __u64 value;
   __u64 value1;
   __u64 value2;
   __u64 value3;
   __u64 value4;
   ...
   __u64 value100;
};

And, even if I pass the address of an instance of this structure, eBPF verifier announces that the program exceeds the limit of the stack. Why is that?

I’m aware that using per-cpu array might be a good way to store these large values that can be passed between functions, but I’d prefer to have as little lookups as possible.