Linkable loadable extensions “module” sample

Overview

This sample demonstrates the use of the Linkable Loadable Extensions (LLEXT) subsystem in Zephyr. The llext subsystem allows for the loading of relocatable ELF files at runtime; their symbols can be accessed and functions called.

Specifically, this shows how to call a simple “hello world” function, implemented in samples/subsys/llext/modules/src/hello_world_ext.c. This is achieved in two different ways, depending on the value of the Kconfig symbol CONFIG_HELLO_WORLD_MODE:

if it is y, the function is directly compiled and called by the Zephyr application. The caller code used in this case is in samples/subsys/llext/modules/src/main_builtin.c.
if it is m, the function is compiled as an llext and it is included in the application as a binary blob. At runtime, the llext subsystem is used to load the extension and call the function. The caller code is in samples/subsys/llext/modules/src/main_module.c.

Requirements

A board with a supported llext architecture and console. This can also be executed in QEMU emulation on the qemu_xtensa or qemu_cortex_r5 virtual boards.

Building and running

The following commands build and run the sample so that the files are linked together in the same binary:

west build -b qemu_xtensa -T sample.llext.modules.builtin_build samples/subsys/llext/modules
west build -t run

The following commands build and run the sample so that the extension code is compiled separately and included in the Zephyr image as a binary blob:
```
west build -b qemu_xtensa -T sample.llext.modules.module_build samples/subsys/llext/modules
west build -t run
```
Take a look at samples/subsys/llext/modules/sample.yaml for the additional architecture-specific configurations required in this case.

To build for a different board, replace qemu_xtensa in the commands above with the desired board name.