1. Linker Script Ld

1.1 Load Address LMA and Run Address VMA

1.1.1 Load Address LMA

• When programming, the addresses where the code segment and data segment are stored are generally in FLASH.
• This storage address ensures that data is not lost when power is off.

1.1.2 Run Address VMA

• During software execution, the (virtual) addresses of the code segment and data segment can be in FLASH or SRAM.
• If VMA is in SRAM, it needs to load from LMA, that is, copy from FLASH to SRAM, such as .data.

1.2 Program Storage Mechanism

1.2.1 Overview

After the project is compiled, it generally displays information such as code size:

It is roughly divided into code segment and data segment, stored in FLASH and SRAM.

1.2.2 General Structure

• Regular code is placed in FLASH, and variables are in SRAM. Upon powering on, data is loaded from LMA to VMA.

• Similarly, other contents of FLASH can also be defined in SRAM, loaded from FLASH to SRAM upon powering on.

1.3 Role of Ld

Tells the linker how to combine various object files into the final executable file, including:

• Specifying the program entry point, i.e., where to start executing the program.

• Defining memory layout, including allocation layout for code segment, data segment, heap, and stack.

1.4 Basic Syntax and Rules of Ld

This section does not intend to introduce syntax specifications, just highlight what is needed. For the complete details, you can search on the engine, such as:

cnblogs.com/jianhua1992/p/16852784.html

1.4.1 The Two Most Important Commands

• MEMORY: Memory Command
• SECTIONS: Segment Command

The content of the commands is enclosed in curly braces, such as:

1.4.2 Introduction to SECTIONS

Allocates code segment, data segment, heap, and stack. A linker script can contain multiple SECTIONS commands, although it is relatively rare to use this way:

1.4.3 Location Counter “.”

The English character 【.】 can be seen everywhere, and can be simply thought of as a pointer to FLASH or SRAM:

• Points to the current address of the current memory, continuously increasing.
• Can be assigned a value, such as:
• 【. += 0x10000;】
• 【. = 0x10000;】
• Can retrieve the current address: 【_sdata = .;】

1.4.4 The Role of “> and AT>

Common usage:

• > corresponds to the run area
• AT> corresponds to the load area

The following diagram shows the code/data being programmed into FLASH and loaded into SRAM for execution upon powering on.

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