CODEWITHSUNDEEP
assemblyx86nasm
Grevak
Grevak

Reputation: 543

What does double dollar sign mean in x86 assembly (NASM)

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?

Upvotes: 13

Views: 5527

Answers (2)

Νίκος Αντωνετσής
Νίκος Αντωνετσής

Reputation: 85

$$ evaluates to the beginning of the current section. you could find it in nasm documentation here : https://nasm.us/doc/nasmdoc3.html#section-3.5

Upvotes: 0

Paul R
Paul R

Reputation: 212979

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.

Upvotes: 30

Related Questions