In [this][1] innocuous-looking commit I made the x86_64 dynamic registrar
crash when TRACE is defined. The underlying problem is that CallState's rsi
field is re-used as rax upon exit of the trampoline. This means that the
CallState.sel () function that gets the selector, will instead get the return
value upon exit. When TRACE is defined, we try to print the selector upon
exiting the trampoline, and since the rsi field is now the rax field, we end
up trying to print the return value as if it were a selector, and things go
slightly sideways.
[1]: https://github.com/xamarin/xamarin-macios/commit/464882d14a83
Rolf Bjarne Kvinge