Development tools for Zephyr on STM32Workbench for Zephyr: VS Code extension to set up, build, flash and debug Zephyr applications on STM32.Devicetree manager: browse, edit and visualize Zephyr devicetree, STM32CubeMX-like for Zephyr.
It seemed that GCC 4.9.3 caused the problem. I have an ATMEL ARM project, which is compiled using GCC 4.8.4, but `FLASH' overflowed by xxxx bytes using GCC 4.9.3.