Template for building firmware for STM32F103 with the LLVM toolchain instead of gcc-arm-none-eabi without LTO support. LTO is available here, and linking with Rust code might be possible.
If LLVM/Clang is installed on your host environment, it is already capable of cross-compiling. But prebuilt libc and libm for the target CPU can be found here: https://github.com/ARM-software/LLVM-embedded-toolchain-for-Arm/releases, lib/clang-runtimes/arm-none-eabi/armv7m_soft_nofp. Note: this is not the best choice for Cortex-M4F core MCUs like STM32F3xx, STM32F4xx.
Startup program file and linker script for STM32F1xx: https://github.com/STMicroelectronics/cmsis_device_f1, Source/Templates/gcc. startup_stm32f103xb.s is for medium-density devices. In case of the startup program here causes problem, use an older one from gcc_ride7 (found elsewhere).
In the linker script file, mark section ._user_heap_stack (and probably .bss) with (NOLOAD) to solve the 384 MiB (0x20000000 - 0x08000000) bin file problem.
Try change the flag -O3 to -O1 in Makefile if strange problem occurred after the migration, because optimization in LLVM is more aggressive.
make flash ARM_LIB_DIR=<armv7m_soft_nofp>
<armv7m_soft_nofp> can be <toolchain>/lib/clang-runtimes/arm-none-eabi/armv7m_soft_nofp.
If make has been executed without DEBUG=1, do make clean.
make flash DEBUG=1 ARM_LIB_DIR=<armv7m_soft_nofp>
make debug
Or do it manually:
make flash DEBUG=1 ARM_LIB_DIR=<armv7m_soft_nofp>
openocd -f /usr/share/openocd/scripts/interface/stlink.cfg -f /usr/share/openocd/scripts/target/stm32f1x.cfg
gdb-multiarch arm-llvm-stm32f103-blinky.elf -iex 'target remote localhost:3333' -iex 'monitor reset halt' -ex 'break main' -ex 'c'