micropython.mk being ignored

[ma261065]

Hi all,

I'm building a C module, and have set up the folder structure as shown at https://docs.micropython.org/en/latest/develop/cmodules.html

my_project/
└── modules/
├── example1/
│ ├── example1.c
│ ├── micropython.mk
│ └── micropython.cmake
└── micropython.cmake

My module compiles fine, and I can successfully call it from MicroPython code.

I wanted to add some compiler flags, so put them in micropython.mk, but they didn't seem to take effect.

After further troubleshooting, it seems that the whole micropython.mk file is being ignored. I can put any garbage in there, and it will still compile successfully. I can even rename the file, and my module will still compile. I am doing a clean between compiles.

What am I missing to make it use the micropython.mk file as per the documentation?

[andrewleech]

Which port / chip are you compiling for? rp2 and esp use cmake so extra definitions need to go in the micropython.cmake fragment. Other make based ports use micropython.mk

[ma261065]

Well, for the life of me I can't get any compiler flags set in micropython.cmake to actually work.

For example, if I set various -O flags using set_source_files_properties (e.g. -O3 or -Os) the compiled code size is exactly the same. I can put invalid options in there (e.g. -O9) and the compiler doesn't complain.

However, if I put #pragma GCC optimize "O3" or #pragma GCC optimize "Os" in the source file I can see the code size change.

How do I get flags in micropython.cmake to work?

[andrewleech]

Yeah I hate cmake. For something so powerful it's got too many obscurities in how to make things actually work.

Can you share your micropython.cmake contents with your attempts to set the flag?

[ma261065]

Here it is.

I tried COMPILE_OPTIONS as well as COMPILE_FLAGS, with and without quotes around the flag, with and without the leading - on the option.

# Create an INTERFACE library for our C module.
add_library(usermod_Decoder INTERFACE)

# Add our source files to the lib
target_sources(usermod_Decoder INTERFACE
${CMAKE_CURRENT_LIST_DIR}/example1.c
${CMAKE_CURRENT_LIST_DIR}/example2.cpp
)

# Add the current directory as an include directory.
target_include_directories(usermod_Decoder INTERFACE
${CMAKE_CURRENT_LIST_DIR}
)

# Set compiler options for specific source files
set_source_files_properties(${CMAKE_CURRENT_LIST_DIR}/example1.c PROPERTIES COMPILE_OPTIONS -O3)
set_source_files_properties(${CMAKE_CURRENT_LIST_DIR}/example2.cpp PROPERTIES COMPILE_OPTIONS -Os)

# Link our INTERFACE library to the usermod target.
target_link_libraries(usermod INTERFACE usermod_Decoder)

[andrewleech]

What you've done certainly looks about right... I'm seeing a couple of references to COMPILE_FLAGS instead of COMPILE_OPTIONS, maybe try

set_source_files_properties(${CMAKE_CURRENT_LIST_DIR}/example1.c PROPERTIES COMPILE_FLAGS -O3)

However it also looks like built-in settings might get in the way of that, or override that, eg. https://stackoverflow.com/questions/47926404/cmake-per-file-optimizations

[andrewleech]

This gives another suggestion: https://jeremimucha.com/2021/02/cmake-fundamentals-part5/ in section "Project configuration interface targets

add_library(usermod_Decoder INTERFACE)
target_compile_options(usermod_Decoder INTERFACE -O3)

though that'll affect all files in the user c module. Perhaps the "generator" in the example on that page that sets something on just c++ files could be adjusted to only set something on a file with particular name.