Question: How can I manually add the line CONFIG\_XILINX\_FIXED\_DEVTREE\_ADDR=y to the linux config file? It keeps getting overwritten when I build the kernel

Answer: 
You can build by `make CONFIG_XILINX_FIXED_DEVTREE_ADDR=y` without adding it into *.config*. But if you gonna add it to .config, you should use `make menuconfig` to select it and save it into *.config*.
If the config variable you're trying to add is new (as in, not in `.config` at all and not showing up in `make menuconfig`), then you should add it to the relevant Kconfig file. For instance, if you look at `fs/proc/Kconfig`, you can see how different `proc` config options are laid out. Follow their example and add your config variable, its variable type, the default, and its description. Then you should see it in `make menuconfig`.

Here's an example of a config variable definition in `fs/proc/Kconfig`:

```
config PROC_VMCORE
    bool "/proc/vmcore support"
    depends on PROC_FS && CRASH_DUMP
    default y
    help
      Exports the dump image of crashed kernel in ELF format.

```