What is the problem with stack walkback?
The calling convention needs a lot of information about each function to walk back up the stack. Much of this information is stored in the executable as auxillary information, separate from the actual code. The result is that object files are much larger, often as much as twice as large as they would be on 32-bit x86. Pulling together all the information necessary to walk back up the stack means that C++ exception processing, Java exception processing, POSIX thread cancellation, etc, will be relatively slow.
