usercmodule example fails to link

[assumptionsoup]

CircuitPython version

main branch

Code/REPL

>>> make BOARD=itsybitsy_nrf52840_express USER_C_MODULES=../../examples/usercmodule

Use make V=1, make V=2 or set BUILD_VERBOSE similarly in your environment to increase build verbosity.
Including User C Module from ../../examples/usercmodule/cexample
Including User C Module from ../../examples/usercmodule/cppexample
mkdir -p build-itsybitsy_nrf52840_express/genhdr
GEN build-itsybitsy_nrf52840_express/genhdr/moduledefs.h
QSTR updated
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: firmware.elf.lto.o:(.rodata.cppfunc_obj+0x4): undefined reference to `cppfunc'
collect2: error: ld returned 1 exit status
make: *** [Makefile:251: build-itsybitsy_nrf52840_express/firmware.elf] Error 1

Here's the verbose output

Behavior

Circuitpython fails to link when the USER_C_MODULES flag is set to the example module path ../../examples/usercmodule

Description

No response

Additional information

I'm building on WSL v2 with the default ubuntu distro.

[jepler]

Hi, thanks for reporting this. I looked into it a bit, and it's more in depth than I initially thought.

It appears the reason it broke between 6.3.0 and now is that upstream added support for C++ code in USER_C_MODULES and we didn't check whether it worked anymore.

I tried a few ports in micropython v1.17, which is what we're currently based off of, and both bare-arm and their (unrelated) nrf port failed with different errors.

Here's a patch which makes it work for raspberrypi (rp2040), where "work" is defined as "it compiled, but I didn't actually test it". https://gist.github.com/8f6e978b5ab7a6c5df0b6b1b698fa68d -- I know you asked about nrf, but rp2040 is what I tinkered with to start.

If you do get this working, please supply a patch, and consider working with micropython on their ports so that USER_C_MODULES works with C++ there as well.