I’m using all the same flags I normally use with gcc.
The a typical compile command looks something like this:
/Users/kamil/tmp/clang+llvm-10.0.0-x86_64-apple-darwin/bin/clang --sysroot=/usr/local/bin/../arm-none-eabi -DARM -DSTM32F401VETx -DSTM32F401xC -DSTM32F4xx -DUSE_FULL_LL_DRIVER -I/Users/kamil/xxx/cmake/../Drivers/STM32F4xx_HAL_Driver/Inc -I/Users/kamil/xxx/Project/Inc -I/Users/kamil/xxx/cmake/../Drivers/CMSIS/Device/ST/STM32F4xx/Include -I/Users/kamil/xxx/cmake/../Drivers/CMSIS/CMSIS/Include -Og -DDEBUG -g -gdwarf-2 -fdata-sections -ffunction-sections -mthumb -mfloat-abi=hard -mfpu=fpv4-sp-d16 -mcpu=cortex-m4 -o CMakeFiles/stm32hal.dir/Users/kamil/xxx/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_cortex.c.o -c /Users/kamil/xxx/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_cortex.c
I noticed I also get these warnings during the process:
clang-10: **warning:** argument unused during compilation: '-mthumb' [-Wunused-command-line-argument]
clang-10: **warning:** argument unused during compilation: '-mfloat-abi=hard' [-Wunused-command-line-argument]
clang-10: **warning:** argument unused during compilation: '-mfpu=fpv4-sp-d16' [-Wunused-command-line-argument]
clang-10: **warning:** argument unused during compilation: '-mcpu=cortex-m4' [-Wunused-command-line-argument]