How Does C++ Linking Work in Practice? [Duplicate]

EDIT: I have moved this answer to the duplicate:

This answer focuses on address relocation, which is one of the crucial functions of linking.

A minimal example will be used to clarify the concept.

0) Introduction

Summary: relocation edits the .text section of object files to translate:

• object file address
• into the final address of the executable

This must be done by the linker because the compiler only sees one input file at a time, but we must know about all object files at once to decide how to:

• resolve undefined symbols like declared undefined functions
• not clash multiple .text and .data sections of multiple object files

Prerequisites: minimal understanding of:

• x86-64 or IA-32 assembly
• global structure of an ELF file. I have made a tutorial for that

Linking has nothing to do with C or C++ specifically: compilers just generate the object files. The linker then takes them as input without ever knowing what language compiled them. It might as well be Fortran.

So to reduce the crust, let's study a NASM x86-64 ELF Linux hello world:

section .data
    hello_world db "Hello world!", 10
section .text
    global _start
    _start:

        ; sys_write
        mov rax, 1
        mov rdi, 1
        mov rsi, hello_world
        mov rdx, 13
        syscall

        ; sys_exit
        mov rax, 60
        mov rdi, 0
        syscall

compiled and assembled with:

nasm -felf64 hello_world.asm            # creates hello_world.o
ld -o hello_world.out hello_world.o     # static ELF executable with no libraries

with NASM 2.10.09.