SW4STM32 and SW4Linux fully supports the STM32MP1 asymmetric multicore Cortex/A7+M4 MPUs

   With System Workbench for Linux, Embedded Linux on the STM32MP1 family of MPUs from ST was never as simple to build and maintain, even for newcomers in the Linux world. And, if you install System Workbench for Linux in System Workbench for STM32 you can seamlessly develop and debug asymmetric applications running partly on Linux, partly on the Cortex-M4.
You can get more information from the ac6-tools website and download (registration required) various documents highlighting:

System Workbench for STM32

The discussion of standard IO dynamic switching among semihost, UARTx, and NULL on STM32



If you only want to implement console I/O using semihosting, the best way to go would probably be to add a file defining the __io_getchar and __io_putchar functions called by read/write as defined in syscalls.c as well as the initialise_function_handles function.

To avoid multiple definitions you must make the empty initialise_monitor_handles function to be weak in syscalls.c by adding __attribute__((weak)) in front of its definition.

To call initialise_monitor_handles can be done directly from the startup code (adding “bl initialise_monitor_handles” before “bl main”) but you can avoid modifying the startup file (which is in assembly language) by adding the constructor attribute to your definition of initialise_monitor_handles:
__attribute__((constructor)) void initialise_monitor_handles()  {
    // Your initialisation code

Then if you include your file, you get semihosting, if you don’t, you don’t even try to initialise it...

Bernard (Ac6)