Cannot construct an object as a static variable in a function #207

leiradel · 2021-03-04T18:25:54Z

I have a function to create a singleton of a class, but the linker complains about some missing functions.

lrcpp::Frontend& lrcpp::Frontend::getInstance() {
    static uint8_t fsmMemory[sizeof(CoreFsm)] alignas(CoreFsm);
    static Frontend singleton(fsmMemory);

    return singleton;
}

$ make clean && make
  CLEAN  /home/leiradel/Develop/circle/sample/libretro
  CPP   frontend/Main.o
  CPP   frontend/Kernel.o
  CPP   frontend/Frontend.o
  CPP   frontend/Fifo.o
  CC    core/main.o
  CPP   lrcpp/src/Components.o
  CPP   lrcpp/src/Core.o
  CPP   lrcpp/src/CoreFsm.o
  CPP   lrcpp/src/Frontend.o
  LD    kernel8.elf
aarch64-linux-gnu-ld: lrcpp/src/Frontend.o: in function `lrcpp::Frontend::getInstance()':
/home/leiradel/Develop/circle/sample/libretro/lrcpp/src/Frontend.cpp:65: undefined reference to `__cxa_guard_acquire'
aarch64-linux-gnu-ld: /home/leiradel/Develop/circle/sample/libretro/lrcpp/src/Frontend.cpp:65: undefined reference to `__cxa_guard_release'
make: *** [../../Rules.mk:155: kernel8.img] Error 1

These functions prevent the static variables from being initialized more than once should two threads try to get the singleton at the same time. I'm using an #idef to special case it when building with Circle, but I think it would be better if Circle supported it directly.

The text was updated successfully, but these errors were encountered:

rsta2 · 2021-03-04T20:19:23Z

This is supported too, if you use the circle-stdlib project. In Circle itself you can add the following to your project Makefile before the include statement for Rules.mk to suppress the errors:

CPPFLAGS += -fno-threadsafe-statics

Because Circle doesn't have a preemptive scheduler, this should work.

leiradel · 2021-03-04T21:08:03Z

Because Circle doesn't have a preemptive scheduler, this should work.

But it's a problem if you use multiple cores.

This is supported too, if you use the circle-stdlib project.

It seems I really need to integrate circle-stdlib into my project :)

rsta2 · 2021-03-05T11:34:54Z

Because Circle doesn't have a preemptive scheduler, this should work.

But it's a problem if you use multiple cores.

That's true. Unfortunately the precise semantics of __cxa_guard_*() is currently not that clear to me, so that I can implement it in Circle. If is is possible to implement it, it will take longer in any way.

leiradel · 2021-03-05T18:30:24Z

I understand. There's a open source implementation (cxa_guard.cxx) that maybe could be used, but that's not critical and entire up to you. The license is this one I believe.

For now I just have the #ifdef I mentioned above and it's working just fine. Feel free to close this issue if you're not planing on implementing this in Circle itself, and thanks for pointing me to circle-stdlib.

rsta2 · 2021-03-06T12:10:22Z

Thanks for the link! I will see, what I can do.

Requires the implementation of the functions __cxa_guard_acquire() and __cxa_guard_release(), which will be automatically used by the compiler. Issue #207

rsta2 · 2021-03-21T11:02:01Z

This feature has been implemented on the develop branch now.

rsta2 · 2021-05-14T08:41:02Z

This feature has been implemented in Circle 44. So this can be closed.

rsta2 added a commit that referenced this issue Mar 21, 2021

Support static objects inside of functions

1526852

Requires the implementation of the functions __cxa_guard_acquire() and __cxa_guard_release(), which will be automatically used by the compiler. Issue #207

rsta2 closed this as completed May 14, 2021

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