llext: Shell loader sample

Adds a sample application that can be used for trying out llext
with the shell. The docs cover how to load a hello world ELF
on to the device, assuming its an arm v7 architecture.

Signed-off-by: Tom Burdick <thomas.burdick@intel.com>

samples/subsys/llext/llext.rst

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+.. _llext-samples:
+
+Linkable Loadable Extension Samples
+###################################
+
+.. toctree::
+   :maxdepth: 1
+   :glob:
+
+   **/*

samples/subsys/llext/shell_loader/CMakeLists.txt

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+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.20.0)
+
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(fs_shell)
+
+FILE(GLOB app_sources src/*.c)
+target_sources(app PRIVATE ${app_sources})

samples/subsys/llext/shell_loader/README.rst

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+.. zephyr:code-sample:: llext-shell-loader
+   :name: Linkable loadable extensions shell module
+   :relevant-api: llext
+
+   Manage loadable extensions using shell commands.
+
+Overview
+********
+
+This example provides shell access to the :ref:`llext` system and provides the
+ability to manage loadable code extensions in the shell.
+
+Requirements
+************
+
+A board with shell capable console.
+
+Building
+********
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/subsys/llext/shell_loader
+   :goals: build
+   :compact:
+
+.. note:: You may need to disable memory protection for the sample to work (e.g. CONFIG_ARM_MPU=n).
+
+Running
+*******
+
+Once the board has booted, you will be presented with a shell prompt.
+All the llext system related commands are available as sub-commands of llext
+which can be seen with llext help
+
+.. code-block:: console
+
+  uart:~$ llext help
+  llext - Loadable extension commands
+  Subcommands:
+    list          :List loaded extensions and their size in memory
+    load_hex      :Load an elf file encoded in hex directly from the shell input.
+                   Syntax:
+                   <ext_name> <ext_hex_string>
+    unload        :Unload an extension by name. Syntax:
+                   <ext_name>
+    list_symbols  :List extension symbols. Syntax:
+                   <ext_name>
+    call_fn       :Call extension function with prototype void fn(void). Syntax:
+                   <ext_name> <function_name>
+
+A hello world C file can be found in tests/subsys/llext/hello_world/hello_world.c
+
+This can be built into a relocatable elf usable on arm v7 platforms. It can be
+inspected with some binutils to see symbols, sections, and relocations.
+Then using additional tools converted to a hex string usable by the llext
+load_hex shell command.
+
+On a host machine with the zephyr sdk setup and the arm toolchain in PATH
+
+.. code-block:: console
+
+  $ arm-zephyr-eabi-gcc -mlong-calls -mthumb -c -o hello_world.elf tests/subsys/llext/hello_world/hello_world.c
+  $ arm-zephyr-eabi-objdump -x -t hello_world.elf
+
+  hello_world.elf:     file format elf32-littlearm
+  hello_world.elf
+  architecture: armv4t, flags 0x00000011:
+  HAS_RELOC, HAS_SYMS
+  start address 0x00000000
+  private flags = 0x5000000: [Version5 EABI]
+
+  Sections:
+  Idx Name          Size      VMA       LMA       File off  Algn
+    0 .text         00000024  00000000  00000000  00000034  2**2
+                    CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
+    1 .data         00000000  00000000  00000000  00000058  2**0
+                    CONTENTS, ALLOC, LOAD, DATA
+    2 .bss          00000000  00000000  00000000  00000058  2**0
+                    ALLOC
+    3 .rodata       0000000d  00000000  00000000  00000058  2**2
+                    CONTENTS, ALLOC, LOAD, READONLY, DATA
+    4 .comment      00000021  00000000  00000000  00000065  2**0
+                    CONTENTS, READONLY
+    5 .ARM.attributes 0000002a  00000000  00000000  00000086  2**0
+                    CONTENTS, READONLY
+  arm-zephyr-eabi-objdump: hello_world.elf: not a dynamic object
+  SYMBOL TABLE:
+  00000000 l    df *ABS*	00000000 hello_world.c
+  00000000 l    d  .text	00000000 .text
+  00000000 l    d  .data	00000000 .data
+  00000000 l    d  .bss	00000000 .bss
+  00000000 l    d  .rodata	00000000 .rodata
+  00000000 l    d  .comment	00000000 .comment
+  00000000 l    d  .ARM.attributes	00000000 .ARM.attributes
+  00000000 g     F .text	00000020 hello_world
+  00000000         *UND*	00000000 printk
+
+
+  RELOCATION RECORDS FOR [.text]:
+  OFFSET   TYPE              VALUE
+  00000018 R_ARM_ABS32       .rodata
+  0000001c R_ARM_ABS32       printk
+
+  $ xxd -p hello_world.elf | tr -d '\n'
+
+
+The resulting hex string can be used to load the extension.
+
+.. code-block:: console
+
+  uart:~$ llext load_hex hello_world 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
+
+This extension can then be seen in the list of loaded extensions (`list`), its symbols printed (`list_symbols`), and the hello_world
+function which the extension exports can be called and run (`call_fn`).
+
+.. code-block:: console
+
+  uart:~$ llext call_fn hello_world hello_world
+  hello world

samples/subsys/llext/shell_loader/prj.conf

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+CONFIG_LOG=y
+CONFIG_LOG_MODE_IMMEDIATE=y
+
+CONFIG_SHELL=y
+CONFIG_SHELL_CMD_BUFF_SIZE=32768
+CONFIG_SHELL_LOG_LEVEL_INF=y
+CONFIG_SHELL_STACK_SIZE=8192
+
+CONFIG_LLEXT=y
+CONFIG_LLEXT_LOG_LEVEL_DBG=y
+CONFIG_LLEXT_HEAP_SIZE=32
+CONFIG_LLEXT_SHELL=y

samples/subsys/llext/shell_loader/sample.yaml

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+sample:
+  description: Loadable extensions with shell sample
+  name: Extension loader shell
+tests:
+  sample.llext.shell:
+    tags: shell llext
+    harness: keyboard
+    filter: not CONFIG_CPU_HAS_MMU
+    arch_allow: arm
+    extra_configs:
+      - CONFIG_ARM_MPU=n
+    # Broken platforms
+    platform_exclude:
+      - nuvoton_pfm_m487 # See #63167

samples/subsys/llext/shell_loader/src/main.c

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+/*
+ * Copyright (c) 2023 Intel Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+
+#define LOG_LEVEL CONFIG_LOG_DEFAULT_LEVEL
+#include <zephyr/logging/log.h>
+LOG_MODULE_REGISTER(app);
+
+int main(void)
+{
+	return 0;
+}