If you use the option "--config=<file>" to load a configuration file for your kernel, you will get the output:

/usr/bin/genkernel: line 38: /gen_funcs.sh: No such file or directory
Could not read /gen_funcs.sh

Even if you use --menuconfig and load your configuration file with the "Load configuration file" menu, it will not use this configuration until you save the loaded configuration to ".config".