The backtrace consists of only addresses.
I attached the output of stap + staprun,
readelf -a on the target executable and
of its .gnu_debuglink
and also the "readelf -debug-dump=frames target_executable".
One thing I noticed while trying to get more insight of what's happening,
was that if I define UNW_PC_FROM_RA to be 1, in -debug-dump=frames
the symbol is resolved but unwind() will only unwind the topmost frame.