I want to use stm32CubeIDE's GCC compiler to compile my project, but the program takes up too much Flash space

[Lucky Dog]

The optimization options for GCC compilation are: Optimize for size(-Os),The compiled result is as follows:

The size of MCU Flash resources occupied is: text+data = 47264 Byte

The.ld link script is shown below:

Question: In my program, the.data segment data (initialized variable) can not be 15K, in theory only 0x44 bytes size, this can be seen from the map file, as shown below:

I compiled the same project program using Keil and everything worked fine. What is the problem with me, or the GCC compiler?

Thanks.

Below is the complete linked script file.

/*
******************************************************************************
**
** @file        : LinkerScript.ld
**
** @author      : Auto-generated by STM32CubeIDE
**
** @brief       : Linker script for STM32L451CEUx Device from STM32L4 series
**                      512Kbytes FLASH
**                      160Kbytes RAM
**                      32Kbytes RAM2
**
**                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) 2022 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 */
 
 
_RAM2_START_ADDR = 0x10000000; 
_RAM2_Size = 32K - 4; 
_RAM2_BOOT_START_ADDR = 0x10000000 + _RAM2_Size;
/* Memories definition */
MEMORY
{
  RAM     (xrw)    : ORIGIN = 0x20000000,   LENGTH = 128K
  RAM2    (xrw)    : ORIGIN = _RAM2_START_ADDR,   LENGTH = _RAM2_Size
  RAM2_BOOT    (xrw)    : ORIGIN = _RAM2_BOOT_START_ADDR,   LENGTH = 4 
  FLASH    (rx)    : ORIGIN = 0x8008000,   LENGTH = 80K
}
 
/* 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
 
  /* 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   : {
    . = ALIGN(4);
    *(.ARM.extab* .gnu.linkonce.armextab.*)
    . = ALIGN(4);
  } >FLASH
 
  .ARM : {
    . = ALIGN(4);
    __exidx_start = .;
    *(.ARM.exidx*)
    __exidx_end = .;
    . = ALIGN(4);
  } >FLASH
 
  .preinit_array     :
  {
    . = ALIGN(4);
    PROVIDE_HIDDEN (__preinit_array_start = .);
    KEEP (*(.preinit_array*))
    PROVIDE_HIDDEN (__preinit_array_end = .);
    . = ALIGN(4);
  } >FLASH
 
  .init_array :
  {
    . = ALIGN(4);
    PROVIDE_HIDDEN (__init_array_start = .);
    KEEP (*(SORT(.init_array.*)))
    KEEP (*(.init_array*))
    PROVIDE_HIDDEN (__init_array_end = .);
    . = ALIGN(4);
  } >FLASH
 
  .fini_array :
  {
    . = 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
 
  .ram2_data :
  {
     . = ALIGN(4);
     _sram2 = .;
     *(.ram2_data)
     *(.ram2_data*)
     . = ALIGN(4);
     _eram2 = .; 
  } >RAM2 AT> FLASH
 
  .ram2_boot :
  {
     . = ALIGN(4);
     _sram2_boot = .;
     *(.ram2_boot)
     *(.ram2_boot*)
     . = ALIGN(4);
     _eram2_boot = .; 
  } >RAM2_BOOT AT> FLASH
  
  /* Remove information from the compiler libraries */
  /DISCARD/ :
  {
    libc.a ( * )
    libm.a ( * )
    libgcc.a ( * )
  }
 
  .ARM.attributes 0 : { *(.ARM.attributes) }
}

[TDK]

What is the actual error message?

Even if your text+data is 48k, that's still plenty less than the 128k of RAM, or 80k of FLASH.

[Lucky Dog]

It is true that the current program size will not exceed the MCU Flash limit, but I want to reduce the Bin file size as much as possible and reduce the time required for firmware upgrade.

Thank you for your reply

[waclawek.jan]

} >RAM2 AT> FLASH

} >RAM2_BOOT AT> FLASH

JW

[Lucky Dog]

Sorry，I don't quite understand what you mean.

I forgot to mention that I defined a bunch of global variables into RAM2, about 15k in size, but I didn't initialize them, and they shouldn't be in the .data segment, they should be in the .bss segment. as shown below:

[waclawek.jan]

>RAM2 AT> FLASH means, they are both in RAM2 and in FLASH.

The attribute mechanism of gcc places those data unconditionally into a given section. The implicit magic of splitting to .data and .bss based on explicit initialization applies only to those variables which are not explicitnly assigned to a given section.

.ram2_datas says, size 15.2kB, does that ring a bell?

JW

[Lucky Dog · Accepted solution]

I have just modified the link script, the NOLOAD keyword was added,as follows:

.ram2_data (NOLOAD):
  {
     . = ALIGN(4);
     _sram2 = .;
     *(.ram2_data)
     *(.ram2_data*)
     . = ALIGN(4);
     _eram2 = .; 
  } >RAM2 AT> FLASH
 
  .ram2_boot (NOLOAD):
  {
     . = ALIGN(4);
     _sram2_boot = .;
     *(.ram2_boot)
     *(.ram2_boot*)
     . = ALIGN(4);
     _eram2_boot = .; 
  } >RAM2_BOOT AT> FLASH

The compiled result is as follows:

​ The compiled results are now almost identical to KEIL.

​ Thank you for your reply.