Meaning of dollar sign in gnu assembly labels

Question

What is the meaning of a dollar sign in front of a gnu assembly label?

For example, what is the difference between mov msg, %si and mov $msg, %si

(For more context, I'm playing around with the x86 Bare Metal Examples: https://github.com/cirosantilli/x86-bare-metal-examples/blob/master/bios_hello_world.S)

#include "common.h"
BEGIN
    mov $msg, %si
    mov $0x0e, %ah
loop:
    lodsb
    or %al, %al
    jz halt
    int $0x10
    jmp loop
halt:
    hlt
msg:
    .asciz "hello world"

(What do the dollar ($) and percentage (%) signs represent in assembly intel x86? discusses the general use of % before registers and $ before constants; but, I don't think it lays out the use of $ with labels nearly as clearly as the answer below )

Answer 1

You use $(dollar) sign when addressing a constant, e.g.: movl $1, %eax (put 1 to %eax register) or when handling an address of some variable, e.g.: movl $var, %eax (this means take an address of var label and put it into %eax register). If you don't use dollar sign that would mean "take the value from var label and put it to register".