11.8.1 About Dummy Frames
gdb can call functions in the target code (for example by using the call or print commands). These functions may be breakpointed, and it is essential that if a function does hit a breakpoint, commands like backtrace work correctly.
This is achieved by making the stack look as though the function had been called from the point where gdb had previously stopped. This requires that gdb can set up stack frames appropriate for such function calls.