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

Using STM32F4 Discovery Board as a Programmer and Debugger

Yes. I have a custom STM32F429 board and I can debug it with any of:
- STM32F429-Discovery
- STM32L053-Discovery
- STM32L053-Nucleo
- STM32F411-Discovery
I haven’t tried my STM32L476-Discovery, but I expect it will work as well.

I open the jumpers, connect to the board, and it just works. Make sure to correctly select if the board has STLinkV2 or STLinkV2-1,
and set the interface to SWD (these boards don’t do JTAG).