Dynamic Module Loading

[zephyrbot]

Reported by XiaoHua Yang:

As a user, I hope zephyr support dynamic loading and linking of modules at run-time. This is useful in applications in which the behavior is intended to be changed after deployment. The module loader can load, relocate, and link standard ELF files that can optionally be stripped off their debugging symbols to keep their size down.

(Imported from Jira ZEP-1264)

[hongshui3000]

I wonder if there is any plan to support it in future roadmap?

[mgiaco]

I am too

[dcpleung]

Adding the ability to dynamically allocate stack should be relatively easy at this point.

As for memory space, with MMU, each module can be assigned a virtual memory region. At runtime, the MMU takes care of the mapping. Without MMU, it is going to be tricky.

[hongshui3000]

In the old version of contiki-ng, an elf loader is included. The version after contiki-ng 4.0 does not seem to be supported anymore.
The implementation of the old version should be used as a reference
https://github.com/contiki-ng/contiki-ng/releases/tag/3.x
contiki-ng-3.x.zip\contiki-ng-3.x\core\loader

[galak]

I think it would be good to explain the use cases a bit more. For example do you need to unload the module and load other modules? Do you need to load more than one module?

There could be some simplifying assumptions that we could make vs having a general module loader.

[0Grit]

I have always wanted to use PIE/PIC (Position Independent Executable / Position independent code) with microcontrollers.
Regardless for an MCU some form of dynamic linking will be needed if this use case expects to do it purely within a C/C++ runtime? We are working with a non-virtualized sometimes not contiguous address space.

My initial use case for dynamic linking as a POC would be to create a sort of 3rd stage bootloader that can manage flash partitions, link, and launch generically formatted firmware images.

[galak]

@attzonko how much portability of "modules" is needed? would there need to be ability to build a module that could run against any zephyr build?