I've been using STM32 core from STM32duino without any trouble on VM for the past couple of months. I only need to enable "Deep search for libraries" in order to be able to compile.

I recently switched to stm32 core by STMicroelectronics because the EEPROM library in STM32 doesn't work at all. All the functions return errors at run time. So, I downloaded the new core and built a sketch in Arduino first and it works perfectly. But in VM, it gives me an error for build_opt.h not found in %CurrentUser%\AppData\Local\Temp\VMBuilds\PhysLoggerSTM32\STM32_GenF1\Release. I found a file name "build_opt.h" in a child folder in the same directory. I tried moving it to the parent folder for VM to find it, Now, it does find it but throws me a lot of new errors all of which are thrown at link time: undefined references to functions and variables.

Error linking for board Generic STM32F1 series
(.text.Reset_Handler+0x26)*: undefined reference to SystemInit
Build failed for project 'PhysLoggerSTM32'
 
ld.exe: \core.a(main.cpp.o): in function premain()
main.cpp*: (.text.startup._Z7premainv+0x4): undefined reference to HAL_NVIC_SetPriorityGrouping
 
ld.exe: \core.a(board.c.o): in function init
board.c*: (.text.init+0x0): undefined reference to hw_config_init
 

and so on...

How can I solve it? I've tried restarting VS, creating a new project with the new core, toggling deep search and several other options in the VMicro menu.

Hi, please do provide the info requested above but we are also looking into an issue where the stm cores conflict. 

A workaround, if you uninstall the one you are not using then it should work okay. The requested output will allow us to give more specific instruction.