UnixLib backtrace

This is from the Sargasso thread, but not related to Sargasso, so…

sp: 507f34 __write_backtrace()
sp: 507fa4 __unixlib_raise_signal()
sp: 5057b8 __h_cback()

I’ve noticed other UnixLib programs outputting such unhelpful messages because the backtrace, being limited to three entries, lists the path into the backtrace function rather than how it got there.

How come UnixLib doesn’t track back further, if not to main() then at least far enough to see what triggered the problem…?

The problem here is that __h_cback is the callback handler which can be called in SVC mode and as it’s not a C function, it’s not included in the chain of stack call frames. The way in which it can be called as the callback handler means in effect it is the first stack frame.