Thanks. I think of unwinder information as debuginfo even though, as you point out, it's used outside of debugging contexts all the time. :-)

As for the actual bug:

Unless you're unwinding the stack by walking the linked list of frames threaded through the frame pointer, then each time you unwind a level of the stack, you need to consult a table keyed on instruction pointer to look up how to compute the register contents of the previous frame based on register content of the current frame. One of the registers you can compute this way is the previous frame's stack pointer.

I haven't looked in depth at what the Go runtime is doing exactly, but at a glance, I don't see mention of frame pointers in the linked article, so I'm guessing Go uses the SP-and-unwind-table approach? If so, the real bug here is that the table didn't have separate entries for the two ADDs and so gave incorrect reconstruction instructions for one of them.

If, however, frame pointers are a load-bearing part of the Go runtime, and that runtime failed to update frame pointer (not just the stack pointer) in the contractually mandatory manner, well, that's a codegen bug and needs a codegen fix.

I guess I just don't like, as a matter of philosophy if not practical engineering, having frame pointers at all. Without the frame pointer, the program already contains all the information you need to unwind, at no runtime cost --- you pay for table lookups only when you unwind, not all the time, on straight-line code.

The purist in me doesn't like burning a register for debugging, but you have to use the right tool for the job I guess.