Using frame to switch stacks

Hello everyone,

I'm debugging a library which uses multiple stacks. The documentation 
states that frame / select-frame can be used for this. However I can 
only seem to get it to work with stack and pc address of frames that are 
with in the current stack. Parameter pairs outside the stack (composing 
another stack) yield an invalid frame.

To show this behavior and how I invoke frame I prepared a minimal 
example, containing a program with two stacks and a python script for 
gdb. It can be found here: https://github.com/NotAC0W/gdb-switch-stacks

The repository also contains a more detailed description of the program 
and the output of an example run.

Am I using frame correctly or should I be using different commands?

Thank you very much for your help,

Niklas