How to add custom config lines to a Kconfig fragment?

[Nick_RA]

Using NCS 3.0.2 I have multiple build variants of my project, based on the same custom PCB but with different parts fitted, and different functionality. So I have create different build configs with custom dts files - this works OK.

I would like to add some of my own custom config entries, so I'm trying to use a Kconfig fragment, but whatever I try I get a "ignoring malformed text" error

Here's an example:

config FOO
  bool "foobar"
  default n

Cwarning: ignoring malformed line 'config FOO_BAR'
Cwarning: ignoring malformed line '  bool "foobar"'
Cwarning: ignoring malformed line '  default n'

Where am I going wrong...?

[Hieu]

Hi Nick_RA,

I wonder if you are using the wrong file type. Here is a setup I just tested in NCS v3.0.2 based on just Hello World sample.

c348718_custom_kconfig_250722_01.zip

Hieu

[Nick_RA]

I wonder what you mean by wrong file type? Does it need to be a particular name and extension?

What you seem to have done is made a config for the application; what I need to do is add extra fragments to different build configurations so each build has its own Kconfig add-on.

I saved your config into a text file, then added it to a test build configuration as an Extra Kconfig fragment like so:

source "Kconfig.zephyr"

menu "Custom Kconfig file"

config FOO
  bool "foobar"
  default n

endmenu

but this gives the same result.

(by the way, are the source, menu/endmenu required?)

[Hieu]

Nick_RA said:

What you seem to have done is made a config for the application; what I need to do is add extra fragments to different build configurations so each build has its own Kconfig add-on.

Ah I see. Adding a new Kconfig is exactly what the snippet you shared did, so I thought that was the intention.

If you want Kconfig fragment, you can just create a new .conf file with similar syntax to the familiar prj.conf, like this.

c348718_custom_kconfig_250723_01.zip

Nick_RA said:

I wonder what you mean by wrong file type? Does it need to be a particular name and extension?

Yes. Both file name and extension are significant to the build system. Please refer to both NCS and Zephyr application development guides:

NCS: Application development
Zephyr: Developing with Zephyr