The storage in UnwindContext.stack was changed to a Vec

[philipc]

#595 changed the storage of UnwindContext.stack from an array to a Vec. @nbdd0121 Was this an intentional change? I'm inclined to change it back. I think defaulting to a fixed size allocation is preferable.

[nbdd0121]

IIRC In majority of cases of unwinding this stack is not needed. The previous 4-element storage consumes quite a bit of stack. If you are allowed to allocate then it's better off to just use a Vec so that it doesn't allocate in fast path.

[philipc]

In majority of cases of unwinding this stack is not needed.

It always needs at least one element for the rules, so it needs to allocate in every case:

gimli/src/read/cfi.rs

Line 2010 in 531636d

self.stack.try_push(UnwindTableRow::default()).unwrap();

The previous 4-element storage consumes quite a bit of stack.

That's why the documentation and example suggested putting the UnwindContext on the heap. And if you put the UnwindContext on the heap and reuse it, then allocating it is a once only cost.

The advantage using only 4 elements is that it puts an upper bound on memory usage, and it is sufficient for all CFI in practice.

[nbdd0121]

Ah, the current row. How about store the current row along side with the stack then?