The unw_step() routine advances the unwind cursor cp to the next older, less deeply nested stack frame.
On successful completion, unw_step() returns a positive value if the updated cursor refers to a valid stack frame, or 0 if the previous stack frame was the last frame in the chain. On error, the negative value of one of the error-codes below is returned.
THREAD AND SIGNAL SAFETY
unw_step() is thread-safe. If cursor cp is in the local address-space, this routine is also safe to use from a signal handler.
An unspecified error occurred.
Libunwind was unable to locate the unwind-info needed to complete the operation.
The unwind-info needed to complete the operation has a version or a format that is not understood by libunwind.
The instruction-pointer (``program-counter'') of the next stack frame is invalid (e.g., not properly aligned).
The next stack frame is invalid.
Returned if a call to find_proc_info() returned -UNW_ESTOPUNWIND.
In addition, unw_step() may return any error returned by the find_proc_info(), get_dyn_info_list_addr(), access_mem(), access_reg(), or access_fpreg() call-backs (see unw_create_addr_space(3)).