1.. _code_data_relocation:
2
3Code And Data Relocation
4########################
5
6Overview
7********
8This feature will allow relocating .text, .rodata, .data, and .bss sections from
9required files and place them in the required memory region. The memory region
10and file are given to the :ref:`gen_relocate_app.py` script in the form
11of a string. This script is always invoked from inside cmake.
12
13This script provides a robust way to re-order the memory contents without
14actually having to modify the code.  In simple terms this script will do the job
15of ``__attribute__((section("name")))`` for a bunch of files together.
16
17A regular expression filter can be used to select only the required sections to be relocated.
18
19Details
20*******
21The memory region and file are given to the :ref:`gen_relocate_app.py` script
22through a file where each line specifies a list of files to be placed in the
23given region.
24
25An example of such a file is:
26
27  .. code-block:: none
28
29     SRAM2:/home/xyz/zephyr/samples/hello_world/src/main.c,
30     SRAM1:/home/xyz/zephyr/samples/hello_world/src/main2.c,
31
32This script is invoked with the following parameters:
33``python3 gen_relocate_app.py -i input_file -o generated_linker -c generated_code``
34
35Kconfig :kconfig:option:`CONFIG_CODE_DATA_RELOCATION` option,  when enabled in
36``prj.conf``, will invoke the script and do the required relocation.
37
38This script also trigger the generation of ``linker_relocate.ld`` and
39``code_relocation.c`` files.  The ``linker_relocate.ld`` file creates
40appropriate sections and links the required functions or variables from all the
41selected files.
42
43.. note::
44
45   The text section is split into 2 parts in the main linker script. The first
46   section will have some info regarding vector tables and other debug related
47   info.  The second section will have the complete text section.  This is
48   needed to force the required functions and data variables to the correct
49   locations.  This is due to the behavior of the linker. The linker will only
50   link once and hence this text section had to be split to make room for the
51   generated linker script.
52
53The ``code_relocation.c`` file has code that is needed for
54initializing data sections, and a copy of the text sections (if XIP).
55Also this contains code needed for bss zeroing and
56for  data copy operations from ROM to required memory type.
57
58**The procedure to invoke this feature is:**
59
60* Enable :kconfig:option:`CONFIG_CODE_DATA_RELOCATION` in the ``prj.conf`` file
61
62* Inside the ``CMakeLists.txt`` file in the project, mention
63  all the files that need relocation.
64
65  ``zephyr_code_relocate(FILES src/*.c LOCATION SRAM2)``
66
67  Where the first argument is the file/files and the second
68  argument is the memory where it must be placed.
69
70  .. note::
71
72     function zephyr_code_relocate() can be called  as many times as required.
73
74Additional Configurations
75=========================
76This section shows additional configuration options that can be set in
77``CMakeLists.txt``
78
79* if the memory is SRAM1, SRAM2, CCD, or AON, then place the full object in the
80  sections for example:
81
82  .. code-block:: none
83
84     zephyr_code_relocate(FILES src/file1.c LOCATION SRAM2)
85     zephyr_code_relocate(FILES src/file2.c LOCATION SRAM)
86
87* if the memory type is appended with _DATA, _TEXT, _RODATA or _BSS, only the
88  selected memory is placed in the required memory region.
89  for example:
90
91  .. code-block:: none
92
93     zephyr_code_relocate(FILES src/file1.c LOCATION SRAM2_DATA)
94     zephyr_code_relocate(FILES src/file2.c LOCATION SRAM2_TEXT)
95
96* Multiple regions can also be appended together such as: SRAM2_DATA_BSS.
97  This will place data and bss inside SRAM2.
98
99* Multiple files can be passed to the FILES argument, or CMake generator
100  expressions can be used to relocate a comma-separated list of files
101
102  .. code-block:: none
103
104     file(GLOB sources "file*.c")
105     zephyr_code_relocate(FILES ${sources} LOCATION SRAM)
106     zephyr_code_relocate(FILES $<TARGET_PROPERTY:my_tgt,SOURCES> LOCATION SRAM)
107
108Section Filtering
109=================
110
111By default, all sections of the specified files will be relocated. If
112``FILTER`` is used, a regular expression is provided to select only
113the sections to be relocated.
114
115The regular expression applies to sections names which can be used to
116select the file's symbols when this one has been built with
117``-ffunction-sections`` and ``-fdata-sections`` which is the case by
118default.
119
120  .. code-block:: none
121
122     zephyr_code_relocate(FILES src/file1.c FILTER ".*\\.func1|.*\\.func2" LOCATION SRAM2_TEXT)
123
124The example above will only relocate ``func1()`` and ``func2()`` of file ``src/file1.c``
125
126NOKEEP flag
127===========
128
129By default, all relocated functions and variables will be marked with ``KEEP()``
130when generating ``linker_relocate.ld``.  Therefore, if any input file happens to
131contain unused symbols, then they will not be discarded by the linker, even when
132it is invoked with ``--gc-sections``. If you'd like to override this behavior,
133you can pass ``NOKEEP`` to your ``zephyr_code_relocate()`` call.
134
135  .. code-block:: none
136
137     zephyr_code_relocate(FILES src/file1.c LOCATION SRAM2_TEXT NOKEEP)
138
139The example above will help ensure that any unused code found in the .text
140sections of ``file1.c`` will not stick to SRAM2.
141
142NOCOPY flag
143===========
144
145When a ``NOCOPY`` option is passed to the ``zephyr_code_relocate()`` function,
146the relocation code is not generated in ``code_relocation.c``. This flag can be
147used when we want to move the content of a specific file (or set of files) to a
148XIP area.
149
150This example will place the .text section of the ``xip_external_flash.c`` file
151to the ``EXTFLASH`` memory region where it will be executed from (XIP). The
152.data will be relocated as usual into SRAM.
153
154  .. code-block:: none
155
156     zephyr_code_relocate(FILES src/xip_external_flash.c LOCATION EXTFLASH_TEXT NOCOPY)
157     zephyr_code_relocate(FILES src/xip_external_flash.c LOCATION SRAM_DATA)
158
159Relocating libraries
160====================
161
162Libraries can be relocated using the LIBRARY argument to
163``zephyr_code_relocation()`` with the library name. For example, the following
164snippet will relocate serial drivers to SRAM2:
165
166  .. code-block:: none
167
168    zephyr_code_relocate(LIBRARY drivers__serial LOCATION SRAM2)
169
170Tips
171====
172
173Take care if relocating kernel/arch files, some contain early initialization
174code that executes before code relocation takes place.
175
176Additional MPU/MMU configuration may be required to ensure that the
177destination memory region is configured to allow code execution.
178
179Samples/ Tests
180==============
181
182A test showcasing this feature is provided at
183``$ZEPHYR_BASE/tests/application_development/code_relocation``
184
185This test shows how the code relocation feature is used.
186
187This test will place .text, .data, .bss from 3 files to various parts in the SRAM
188using a custom linker file derived from ``include/zephyr/arch/arm/cortex_m/scripts/linker.ld``
189
190A sample showcasing the NOCOPY flag is provided here: :zephyr:code-sample:`code_relocation_nocopy`.
191