It seems that cuda-gdb uses CUDA Debugger API, but it just reuses the struct definition CUDBGAPI_st in cudadebugger.h and implemented the function pointers by itself. cuda-gdb use IPC to communicate with the driver directly instead of use the functions returned by cudbgGetAPI in cudadebugger.h. This can be confirmed by Ptrace in the kernel function - #2 by agontarek