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unknown in flash after linked-script-user-defined const

carleslsregner
Associate III

I am just curious about information in the flash. 

carleslsregner_0-1768214727900.png

 

#ifndef DEVICE_VERSIONING_INFORMATION_H
#define DEVICE_VERSIONING_INFORMATION_H

typedef struct {
    uint32_t magic;   // 0x46575652 = 'FWVR'
    uint8_t major;
    uint8_t minor;
    uint8_t patch;
    uint8_t build;
} fw_version_t;

__attribute__((used, section(".fw_version")))
const fw_version_t fw_version = {
    .magic = 0x46575652,
    .major = 1,
    .minor = 3,
    .patch = 2,
    .build = 7,
};

#endif // DEVICE_VERSIONING_INFORMATION_H

 

I wrote in the linked script file (.ld) some versioning information. I guess it is the best way to store the device versioning information because that way allows the swd to get directly from the flash the version, although, I can get it too by request and response by uart. 

However, why there is more data after the version information in the flash memory?

carleslsregner_1-1768215451172.png

Is this normal? Should the user defined constants in the flash be followed by other information?

/*
******************************************************************************
**
** @file        : LinkerScript.ld
**
** @author      : Auto-generated by STM32CubeIDE
**
**  Abstract    : Linker script for NUCLEO-F070RB Board embedding STM32F070RBTx Device from stm32f0 series
**                      128KBytes FLASH
**                      16KBytes RAM
**
**                Set heap size, stack size and stack location according
**                to application requirements.
**
**                Set memory bank area and size if external memory is used
**
**  Target      : STMicroelectronics STM32
**
**  Distribution: The file is distributed as is, without any warranty
**                of any kind.
**
******************************************************************************
** @attention
**
** Copyright (c) 2026 STMicroelectronics.
** All rights reserved.
**
** This software is licensed under terms that can be found in the LICENSE file
** in the root directory of this software component.
** If no LICENSE file comes with this software, it is provided AS-IS.
**
******************************************************************************
*/

/* Entry Point */
ENTRY(Reset_Handler)

/* Highest address of the user mode stack */
_estack = ORIGIN(RAM) + LENGTH(RAM); /* end of "RAM" Ram type memory */

_Min_Heap_Size = 0x200; /* required amount of heap */
_Min_Stack_Size = 0x400; /* required amount of stack */

/* Memories definition */
MEMORY
{
  RAM    (xrw)    : ORIGIN = 0x20000000,   LENGTH = 16K
  FLASH    (rx)    : ORIGIN = 0x8000000,   LENGTH = 128K
}

/* Sections */
SECTIONS
{

  /* The startup code into "FLASH" Rom type memory */
  .isr_vector :
  {
    . = ALIGN(4);
    KEEP(*(.isr_vector)) /* Startup code */
    . = ALIGN(4);
  } >FLASH

  /* The program code and other data into "FLASH" Rom type memory */
  .text :
  {
    . = ALIGN(4);
    *(.text)           /* .text sections (code) */
    *(.text*)          /* .text* sections (code) */
    *(.glue_7)         /* glue arm to thumb code */
    *(.glue_7t)        /* glue thumb to arm code */
    *(.eh_frame)

    KEEP (*(.init))
    KEEP (*(.fini))

    . = ALIGN(4);
    _etext = .;        /* define a global symbols at end of code */

  } >FLASH


	/* Firmware version section at fixed address */
    .fw_version 0x08003000 :
    {
        KEEP(*(.fw_version*))
    } >FLASH


  /* Constant data into "FLASH" Rom type memory */
  .rodata :
  {
    . = ALIGN(4);
    *(.rodata)         /* .rodata sections (constants, strings, etc.) */
    *(.rodata*)        /* .rodata* sections (constants, strings, etc.) */
    . = ALIGN(4);
  } >FLASH

  .ARM.extab (READONLY) : /* The "READONLY" keyword is only supported in GCC11 and later, remove it if using GCC10 or earlier. */
  {
    . = ALIGN(4);
    *(.ARM.extab* .gnu.linkonce.armextab.*)
    . = ALIGN(4);
  } >FLASH

  .ARM (READONLY) : /* The "READONLY" keyword is only supported in GCC11 and later, remove it if using GCC10 or earlier. */
  {
    . = ALIGN(4);
    __exidx_start = .;
    *(.ARM.exidx*)
    __exidx_end = .;
    . = ALIGN(4);
  } >FLASH

  .preinit_array (READONLY) : /* The "READONLY" keyword is only supported in GCC11 and later, remove it if using GCC10 or earlier. */
  {
    . = ALIGN(4);
    PROVIDE_HIDDEN (__preinit_array_start = .);
    KEEP (*(.preinit_array*))
    PROVIDE_HIDDEN (__preinit_array_end = .);
    . = ALIGN(4);
  } >FLASH

  .init_array (READONLY) : /* The "READONLY" keyword is only supported in GCC11 and later, remove it if using GCC10 or earlier. */
  {
    . = ALIGN(4);
    PROVIDE_HIDDEN (__init_array_start = .);
    KEEP (*(SORT(.init_array.*)))
    KEEP (*(.init_array*))
    PROVIDE_HIDDEN (__init_array_end = .);
    . = ALIGN(4);
  } >FLASH

  .fini_array (READONLY) : /* The "READONLY" keyword is only supported in GCC11 and later, remove it if using GCC10 or earlier. */
  {
    . = ALIGN(4);
    PROVIDE_HIDDEN (__fini_array_start = .);
    KEEP (*(SORT(.fini_array.*)))
    KEEP (*(.fini_array*))
    PROVIDE_HIDDEN (__fini_array_end = .);
    . = ALIGN(4);
  } >FLASH

  /* Used by the startup to initialize data */
  _sidata = LOADADDR(.data);

  /* Initialized data sections into "RAM" Ram type memory */
  .data :
  {
    . = ALIGN(4);
    _sdata = .;        /* create a global symbol at data start */
    *(.data)           /* .data sections */
    *(.data*)          /* .data* sections */
    *(.RamFunc)        /* .RamFunc sections */
    *(.RamFunc*)       /* .RamFunc* sections */

    . = ALIGN(4);
    _edata = .;        /* define a global symbol at data end */

  } >RAM AT> FLASH

  /* Uninitialized data section into "RAM" Ram type memory */
  . = ALIGN(4);
  .bss :
  {
    /* This is used by the startup in order to initialize the .bss section */
    _sbss = .;         /* define a global symbol at bss start */
    __bss_start__ = _sbss;
    *(.bss)
    *(.bss*)
    *(COMMON)

    . = ALIGN(4);
    _ebss = .;         /* define a global symbol at bss end */
    __bss_end__ = _ebss;
  } >RAM

  /* User_heap_stack section, used to check that there is enough "RAM" Ram  type memory left */
  ._user_heap_stack :
  {
    . = ALIGN(8);
    PROVIDE ( end = . );
    PROVIDE ( _end = . );
    . = . + _Min_Heap_Size;
    . = . + _Min_Stack_Size;
    . = ALIGN(8);
  } >RAM

  /* Remove information from the compiler libraries */
  /DISCARD/ :
  {
    libc.a ( * )
    libm.a ( * )
    libgcc.a ( * )
  }

  .ARM.attributes 0 : { *(.ARM.attributes) }
}

I just ask it out of curiosity. 

 

Thanks for all.

1 ACCEPTED SOLUTION

Accepted Solutions

@Andrew Neil wrote:


Please show your linker script - hard to comment on it without seeing it!


Ah, now you've edited the original post to add it!

 

You've only specified the location of your version information; you haven't said that it has to be the last thing in flash.

The Linker has seen that there is space available beyond your .fw_version section, so it has just used it as normal.

 

PS:

Where to find the official GNU ld and linker script documentation

via: https://stackoverflow.com/a/77868219

A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.

View solution in original post

2 REPLIES 2
Andrew Neil
Super User

@carleslsregner wrote:

I guess it is the best way to store the device versioning information because that way allows the swd to get directly from the flash 


It's certainly a common way to do it.

 


@carleslsregner wrote:

I wrote in the linker script file (.ld)


Please show your linker script - hard to comment on it without seeing it!

 


@carleslsregner wrote:

why there is more data after the version information in the flash memory?


Why wouldn't there be?

What you've shown is all standard C stuff: .preinit_array, .init_array, etc are all part of the GCC startup process for initialising variables...

A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.

@Andrew Neil wrote:


Please show your linker script - hard to comment on it without seeing it!


Ah, now you've edited the original post to add it!

 

You've only specified the location of your version information; you haven't said that it has to be the last thing in flash.

The Linker has seen that there is space available beyond your .fw_version section, so it has just used it as normal.

 

PS:

Where to find the official GNU ld and linker script documentation

via: https://stackoverflow.com/a/77868219

A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.