Zephyr: Enable -O0 for only one *.c file

[Nukersson]

Is it possible to enable -O0 compilation option for one *.c file only in Zephyr's toolchain?

P.S.: In my case I would like use -O0 for one particular eth_stm32_hal.c file.

[tejlmand]

Yes, using native CMake, this is possible:

set_source_file_properties(<path-to>/eth_stm32_hal.c PROPERTIES COMPILE_OPTIONS  "-O0")

https://cmake.org/cmake/help/v3.13/command/set_source_files_properties.html#command:set_source_files_properties

or

set_property(SOURCE <path-to>/eth_stm32_hal.c [APPEND] PROPERTY COMPILE_OPTIONS  "-O0")

But be aware of, that is the specific case of eth_stm32_hal.c, then there is a small detail:

Source file properties are visible only to targets added in the same directory (CMakeLists.txt).

which means, adding this line into https://github.com/zephyrproject-rtos/zephyr/blob/master/drivers/ethernet/CMakeLists.txt will not give the desired effect, as the file is compiled into zephyr lib, defined at top-level CMakeLists.txt file. (and not in the CMakeLists.txt file where eth_stm32_hal.c is added)

So the line would need to be added in:
https://github.com/zephyrproject-rtos/zephyr/blob/master/CMakeLists.txt

which is not so elegant.
(CMake 3.18-rc1 allows the DIRECTORY keyword for better control: https://cmake.org/cmake/help/latest/command/set_source_files_properties.html#command:set_source_files_properties
, but Zephyr only requires 3.13)

Note it is often possible to use ${CMAKE_CURRENT_LIST_DIR} as <path-to> in above example.

[Nukersson]

@tejlmand Thank you very much for very good explanation!

[Nukersson]

@tejlmand based on your good explanation, would it be possible to add additional Zephyr doc's information, on how to use -O0 for separate *.c files?

[tejlmand]

@Nukersson Thanks for your feedback.
Regarding additional docs, then I will consider your suggestion.
There is a fine line between describing useful CMake functionality in scope of Zephyr but avoid to duplicate CMake's own documentation into Zephyr.

In general, compile options are managed through Kconfig, but as your question shows, there are certain cases where there are reasons for using CMake features directly.
So the specific use of set_source_files_properties might be worth documenting.