zephyr/doc/tools/code-relocation.rst

.. _code_data_relocation:

Code data relocation
####################

Overview
********
This script will relocate .text, .rodata, .data, and .bss sections from
required files and place them in the required memory region. The
memory region and file are given to this python script in the form
of a string. This script is always invoked from inside cmake.

This script provides a robust way to re-order
the memory contents without actually having to modify the code.
In simple terms this script will do the job of
``__attribute__((section("name")))`` for a bunch of files together.

Details
*******
The memory region and file are given to this python script in the form of a string.

An example of such a string is:
``SRAM2:/home/xyz/zephyr/samples/hello_world/src/main.c,SRAM1:/home/xyz/zephyr/samples/hello_world/src/main2.c``

This script is invoked with the following parameters:
``python3 gen_relocate_app.py -i input_string -o generated_linker -c generated_code``

Kconfig :option:`CONFIG_CODE_DATA_RELOCATION` option,  when enabled in ``prj.conf``, will
invoke the script and do the required relocation.

This script also trigger the generation of ``linker_relocate.ld`` and ``code_relocation.c`` files.
The ``linker_relocate.ld`` file creates appropriate sections and
links the required functions or variables from all the selected files.

**Note**:
The text section is split into 2 parts in the main linker script. The first section
will have some info regarding vector tables and other debug related info.
The second section will have the complete text section.
This is needed to force the required functions and data variables to the correct locations.
This is due to the behavior of the linker. The linker will only link once and
hence this text section had to be split to make room for the generated linker script.

The ``code_relocation.c`` file has code that is needed for
initializing data sections, and a copy of the text sections (if XIP).
Also this contains code needed for bss zeroing and
for  data copy operations from ROM to required memory type.

**The procedure to invoke this feature is:**

* Enable :option:`CONFIG_CODE_DATA_RELOCATION` in the ``prj.conf`` file

* Inside the ``CMakeLists.txt`` file in the project, mention
  all the files that need relocation.

  ``zephyr_code_relocate(src/*.c SRAM2)``

  Where the first argument is the file/files and the second
  argument is the memory where it must be placed.

 .. note::
    The file argument supports limited regular expressions.
    function zephyr_code_relocate() can be called  as many times as required.
    This step has to be performed before the inclusion of boilerplate.cmake.


Additional Configurations
=========================
This section shows additional configuration options that can be set in ``CMakeLists.txt``

* if the memory is SRAM1, SRAM2, CCD, or AON, then place the full object in the sections
  for example:

  .. code-block:: none

     zephyr_code_relocate(src/file1.c SRAM2)
     zephyr_code_relocate(src/file2.c.c SRAM)

* if the memory type is appended with _DATA, _TEXT, _RODATA or _BSS, only the
  selected memory is placed in the required memory region.
  for example:

  .. code-block:: none

     zephyr_code_relocate(src/file1.c SRAM2_DATA)
     zephyr_code_relocate(src/file2.c.c SRAM2_TEXT)

* Multiple regions can also be appended together such as: SRAM2_DATA_BSS.
  This will place data and bss inside SRAM2.

Sample
======
A sample showcasing this feature is provided at
``$ZEPHYR_BASE/samples/test_relocation/``

This is an example of using the code relocation feature.
This example will place .text, .data, .bss from 3 files to various parts in the SRAM
using a custom linker file derived from ``include/arch/arm/cortex_m/scripts/linker.ld``