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 17Details 18******* 19The memory region and file are given to the :ref:`gen_relocate_app.py` script in the form of a string. 20 21An example of such a string is: 22``SRAM2:/home/xyz/zephyr/samples/hello_world/src/main.c,SRAM1:/home/xyz/zephyr/samples/hello_world/src/main2.c`` 23 24This script is invoked with the following parameters: 25``python3 gen_relocate_app.py -i input_string -o generated_linker -c generated_code`` 26 27Kconfig :kconfig:option:`CONFIG_CODE_DATA_RELOCATION` option, when enabled in 28``prj.conf``, will invoke the script and do the required relocation. 29 30This script also trigger the generation of ``linker_relocate.ld`` and 31``code_relocation.c`` files. The ``linker_relocate.ld`` file creates 32appropriate sections and links the required functions or variables from all the 33selected files. 34 35.. note:: 36 37 The text section is split into 2 parts in the main linker script. The first 38 section will have some info regarding vector tables and other debug related 39 info. The second section will have the complete text section. This is 40 needed to force the required functions and data variables to the correct 41 locations. This is due to the behavior of the linker. The linker will only 42 link once and hence this text section had to be split to make room for the 43 generated linker script. 44 45The ``code_relocation.c`` file has code that is needed for 46initializing data sections, and a copy of the text sections (if XIP). 47Also this contains code needed for bss zeroing and 48for data copy operations from ROM to required memory type. 49 50**The procedure to invoke this feature is:** 51 52* Enable :kconfig:option:`CONFIG_CODE_DATA_RELOCATION` in the ``prj.conf`` file 53 54* Inside the ``CMakeLists.txt`` file in the project, mention 55 all the files that need relocation. 56 57 ``zephyr_code_relocate(FILES src/*.c LOCATION SRAM2)`` 58 59 Where the first argument is the file/files and the second 60 argument is the memory where it must be placed. 61 62 .. note:: 63 64 function zephyr_code_relocate() can be called as many times as required. 65 66Additional Configurations 67========================= 68This section shows additional configuration options that can be set in 69``CMakeLists.txt`` 70 71* if the memory is SRAM1, SRAM2, CCD, or AON, then place the full object in the 72 sections for example: 73 74 .. code-block:: none 75 76 zephyr_code_relocate(FILES src/file1.c LOCATION SRAM2) 77 zephyr_code_relocate(FILES src/file2.c LOCATION SRAM) 78 79* if the memory type is appended with _DATA, _TEXT, _RODATA or _BSS, only the 80 selected memory is placed in the required memory region. 81 for example: 82 83 .. code-block:: none 84 85 zephyr_code_relocate(FILES src/file1.c LOCATION SRAM2_DATA) 86 zephyr_code_relocate(FILES src/file2.c LOCATION SRAM2_TEXT) 87 88* Multiple regions can also be appended together such as: SRAM2_DATA_BSS. 89 This will place data and bss inside SRAM2. 90 91* Multiple files can be passed to the FILES argument, or CMake generator 92 expressions can be used to relocate a comma-separated list of files 93 94 .. code-block:: none 95 96 file(GLOB sources "file*.c") 97 zephyr_code_relocate(FILES ${sources} LOCATION SRAM) 98 zephyr_code_relocate(FILES $<TARGET_PROPERTY:my_tgt,SOURCES> LOCATION SRAM) 99 100NOKEEP flag 101=========== 102 103By default, all relocated functions and variables will be marked with ``KEEP()`` 104when generating ``linker_relocate.ld``. Therefore, if any input file happens to 105contain unused symbols, then they will not be discarded by the linker, even when 106it is invoked with ``--gc-sections``. If you'd like to override this behavior, 107you can pass ``NOKEEP`` to your ``zephyr_code_relocate()`` call. 108 109 .. code-block:: none 110 111 zephyr_code_relocate(FILES src/file1.c LOCATION SRAM2_TEXT NOKEEP) 112 113The example above will help ensure that any unused code found in the .text 114sections of ``file1.c`` will not stick to SRAM2. 115 116NOCOPY flag 117=========== 118 119When a ``NOCOPY`` option is passed to the ``zephyr_code_relocate()`` function, 120the relocation code is not generated in ``code_relocation.c``. This flag can be 121used when we want to move the content of a specific file (or set of files) to a 122XIP area. 123 124This example will place the .text section of the ``xip_external_flash.c`` file 125to the ``EXTFLASH`` memory region where it will be executed from (XIP). The 126.data will be relocated as usual into SRAM. 127 128 .. code-block:: none 129 130 zephyr_code_relocate(FILES src/xip_external_flash.c LOCATION EXTFLASH_TEXT NOCOPY) 131 zephyr_code_relocate(FILES src/xip_external_flash.c LOCATION SRAM_DATA) 132 133Relocating libraries 134==================== 135 136Libraries can be relocated using the LIBRARY argument to 137``zephyr_code_relocation()`` with the library name. For example, the following 138snippet will relocate serial drivers to SRAM2: 139 140 .. code-block:: none 141 142 zephyr_code_relocate(LIBRARY drivers__serial LOCATION SRAM2) 143 144Tips 145==== 146 147Take care if relocating kernel/arch files, some contain early initialization 148code that executes before code relocation takes place. 149 150Additional MPU/MMU configuration may be required to ensure that the 151destination memory region is configured to allow code execution. 152 153Samples/ Tests 154============== 155 156A test showcasing this feature is provided at 157``$ZEPHYR_BASE/tests/application_development/code_relocation`` 158 159This test shows how the code relocation feature is used. 160 161This test will place .text, .data, .bss from 3 files to various parts in the SRAM 162using a custom linker file derived from ``include/zephyr/arch/arm/cortex_m/scripts/linker.ld`` 163 164A sample showcasing the NOCOPY flag is provided at 165``$ZEPHYR_BASE/samples/application_development/code_relocation_nocopy/`` 166