dts: How to manually run the C preprocessor on DTS files?

[soares-sergio]

Hi folks,

Context: I'm trying to learn more about DTS and how it can go from .dts to devicetree.h. I'm working in a non-Zephyr codebase and I'm investigating if it would be possible to reuse Zephyr's DTS tools/bindings so we don't have to duplicate some of this code in our own codebase.

To start, I'm using the mimxrt595_evk_cm33.dts as an example and trying to manually run the steps to convert it into a header file.

1. The first step is to run the C preprocessor on the DTS file to resolve macros and includes. I'm running the cpp command directly and providing include directories manually:

cpp zephyr/boards/arm/mimxrt595_evk/mimxrt595_evk_cm33.dts -Izephyr/include -Izephyr/dts -Izephyr/dts/arm -Izephyr/dts/common -Imodules/hal/nxp/dts -traditional-cpp -o mimxrt595_evk_cm33_preprocessed.dts

It seems to run mostly fine but at the end I get multiple errors such as:

zephyr/include/zephyr/sys/util_macro.h:649: error: syntax error in macro parameter list
  649 | #define MACRO_MAP_CAT_N(N, ...) MACRO_MAP_CAT_N_(N, __VA_ARGS__)

Note: I had to add -traditional-cpp otherwise it would fail on specific macros such as #address-cells etc.
My cpp version is 13.2.0.

Any ideas on what could be wrong? Thanks!

[yashi]

cmake/modules/dts.cmake is the driving functions. In that, you see:

set(GEN_DEFINES_SCRIPT          ${DT_SCRIPTS}/gen_defines.py)

which is scripts/dts/gen_defines.py. At the top of the script you read

# This script uses edtlib to generate a header file from a devicetree
# (.dts) file. Information from binding files in YAML format is used
# as well.