问题
The expression is:
times 512-($-$$) db 0
I know what the dollar sign means but I don't know what it means when it's double.
What does the double dollar sign mean?
回答1:
When all else fails, Read The Fine Manual (section 3.5 "Expressions"):
NASM supports two special tokens in expressions, allowing calculations to involve the current assembly position: the $ and $$ tokens. $ evaluates to the assembly position at the beginning of the line containing the expression; so you can code an infinite loop using JMP $. $$ evaluates to the beginning of the current section; so you can tell how far into the section you are by using ($−$$).
So the example in your question is just padding the current section to a size of 512 with zeroes.
来源：https://stackoverflow.com/questions/46726434/what-does-double-dollar-sign-mean-in-x86-assembly-nasm