Assembly Language Operand Specifiers

Question

I am new to learning assembly language and came across the following expressions:

9(%rax, %rdx)
0xFC(,%rcx,4)
(%rax, %rdx, 4)

I would be really grateful if someone could point me to a resource where I can understand these commands or explain them to me.

Thank you.

Consider reading a tutorial on AT&T assembly syntax. – fuz Sep 28 '16 at 18:58 — fuz, Sep 28 '16 at 18:58

Gabriel Vasconcelos · Accepted Answer · 2016-09-28T19:06:41.747

3

This apparently refers to arithmetic addressing in x86 AT&T assembly.

The syntax is rather simple:

N(%reg1, %reg2, F)

This results in address = N + %reg1 + %reg2 * F. This can be used in multiple instructions for purposes like accessing data inside a struct (C compilers), etc.

For full reference, check this guide.

edited Sep 28 '16 at 19:06

answered Sep 28 '16 at 18:45

Gabriel Vasconcelos

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Thank you so much. The link is really helpful. – Hassaan Hasan Sep 29 '16 at 22:34
That reference leaves out RIP-relative addressing modes, but otherwise looks good. See also [all the available x86 addressing modes](http://stackoverflow.com/a/34058400/224132). – Peter Cordes Oct 01 '16 at 07:38

Assembly Language Operand Specifiers

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