Where a process in a computing system comprises mixed code, having different sections of code managed by different runtimes, the call stack used to coordinate function invocations may comprise call stack frames created according to multiple calling conventions. In order to analyze this call stack in a stack walk or unwinding, a debugger may be configured to request the runtimes managing the process to claim a particular call stack frame, and to request the runtime that claims it to parse the contents of the frame, or to utilize call stack analysis techniques if the call stack frame was created by unmanaged code.