C++ global objects

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1

I’m having trouble declaring global C++ objects. Take the following code:

#include <vector>

std::vector<ztimer_periodic_t> timers2;

int main() {
  return 0;
}

When compiled with the following Makefile

FEATURES_REQUIRED += periph_timer
FEATURES_REQUIRED += cpp libstdcpp 
USEMODULE += ztimer_usec ztimer_msec ztimer_sec cxx_ctor_guards

The errors produced

/usr/lib/gcc/arm-none-eabi/12.2.1/../../../arm-none-eabi/bin/ld: /home/nathaniel/projects/riot/garden/bin/nucleo-f446re/application_garden/main.o: in function `_GLOBAL__sub_I_timers2':
/home/nathaniel/projects/riot/garden/main.cpp:3: undefined reference to `__dso_handle'

I have read that this is caused by guard code for constructors and the documentation says:

This module is intended to be used by platforms that want to provide C++ support, but the used standard C++ library does not provide these guards. In this case, adding this module will do the trick. The programmer / user should never interact with any of the functions.

Note that on some platforms the type __guard is defined differently from the “generic” definition, most notably ARM. For those platforms a header named cxx_ctor_guards_arch.h needs to be created containing the correct typedef and the preprocessor macro CXX_CTOR_GUARDS_CUSTOM_TYPE needs to be defined.

I am working on a STM32-F446RE which is ARM based but I am at a loss as to how to do this. Help would be appreciated.

As a side note, based on some searching adding this line seems to do the trick but seems a dreadful hack:

void *__dso_handle __attribute__((weak)) = NULL;
2

When you add the cpp11-compat module, you will also get this hack (via cpp_new_delete) auto-enabled, so it might not be all that bad.

3

So in the Makefile add USEMODULE += cpp11-compat?