What is Linker Script for ARM - Explained Simply

A linker script for ARM is a plain text file that tells the linker how to arrange program sections in memory by defining memory regions and placing code and data using commands like MEMORY and SECTIONS.

Examples

InputSimple linker script with one memory region

OutputDefines a single RAM region and places all code and data starting at address 0x20000000.

InputLinker script with FLASH and RAM regions

OutputSeparates code into FLASH memory starting at 0x08000000 and data into RAM at 0x20000000.

InputLinker script with custom stack size

OutputReserves a specific memory area for the stack and places it at the top of RAM.

Code

linker_script

/* Simple ARM linker script example */
MEMORY
{
  FLASH (rx) : ORIGIN = 0x08000000, LENGTH = 256K
  RAM (rwx)  : ORIGIN = 0x20000000, LENGTH = 40K
}

SECTIONS
{
  .text :
  {
    *(.text*)
  } > FLASH

  .data :
  {
    *(.data*)
  } > RAM

  .bss :
  {
    *(.bss*)
  } > RAM
}

Output

Defines FLASH and RAM memory regions and places .text section in FLASH and .data and .bss sections in RAM.

Why This Works

Step 1: Define Memory Regions

The MEMORY command specifies physical memory areas like FLASH and RAM with start addresses and sizes.

Step 2: Assign Sections to Memory

The SECTIONS command maps program sections such as .text (code) and .data (initialized data) to these memory regions.

Step 3: Control Program Layout

This script controls where code and data reside in the ARM device's memory, which is critical for correct execution.

Alternative Approaches

Using default linker script

linker_script

No custom linker script; rely on compiler defaults.

Simpler but less control; may not fit specific memory layouts.

Using linker script generator tools

linker_script

Use tools like STM32CubeMX to auto-generate linker scripts.

Faster setup but less learning about memory layout details.

Complexity: O(1) time, O(1) space

Time Complexity

Linker scripts are static configuration files, so they do not affect runtime complexity.

Space Complexity

They define memory layout but do not consume extra runtime memory themselves.

Which Approach is Fastest?

Using a custom linker script or default script has no impact on execution speed; it only affects memory placement.

Approach	Time	Space	Best For
Custom Linker Script	O(1)	O(1)	Precise memory control
Default Linker Script	O(1)	O(1)	Quick setup, less control
Generated Linker Script	O(1)	O(1)	Ease of use with hardware tools