It would be nice to have the port SDCC to this low-cost MCU line from ST Microelectronics. There are AFAIK only two usable compilers - Cosmic and Raisonance. They are targeted only for MS Windows platform.
In STM8 chip, there is bootstrap loader similar like in STM32. Client SW works on Linux properly. So, to develop applications on Linux for STM8, some compiler is necessary then.