Lecture 04

Question 1

In x86 AT&T syntax, the main memory addressing mode is:
disp (%reg1, %reg2, scale)

What is disp?

Answer 1

disp - Displacement. A constant integer. This is also known as the offset

Question 2

In x86 AT&T syntax, the main memory addressing mode is:
disp (%reg1, %reg2, scale)

What is reg1?

Answer 2

The base register of the operand

Question 3

In x86 AT&T syntax, the main memory addressing mode is:
disp (%reg1, %reg2, scale)

What is reg2?

Answer 3

The index register of the operand

Question 4

In x86 AT&T syntax, the main memory addressing mode is:
disp (%reg1, %reg2, scale)

What is scale?

Answer 4

1,2,4 or 8.

This is what the index is multiplied by.

Question 5

In x86 AT&T syntax, the main memory addressing mode is:
disp (%reg1, %reg2, scale)

How are these values combined to calculate the memory address?

Answer 5

address = (reg1) + (scale) * (reg2) + disp

Question 6

in x86 AT&T syntax, you may omit the displacement, scale, and reg2 when accessing a memory address:
(%reg1)
Which accessing mode is this?

Answer 6

Indirect mode

Question 7

in x86 AT&T syntax, you may omit the scale, reg1, and reg2 when accessing a memory address:
disp
Which accessing mode is this?

Answer 7

Direct mode

Question 8

If you wished to use the number 7 as an operand in a line of AT&T x86 assembler, which character would need to precede it?

Answer 8

$

Question 9

A line of assembler ending with a colon is what?

Answer 9

A label.

These are used as names for places in the program, for example for jumps.

Question 10

In AT&T syntax, does the destination of an operation come first, or last?

Answer 10

Last.

For example, ‘movq reg1, reg2’ would be read ‘Copy reg1 to reg2’

Question 11

In C calling conventions for x86-64, how many arguments are stored in registers (Assuming each argument fits within 64 bits)?

Answer 11

6.

The registers rdi, rsi, rdx, rcx, r8, and r9.

Question 12

In C calling conventions for x86-64, where do additional arguments go that cannot fit in the registers?

Answer 12

On the stack.

Question 13

In C calling conventions for x86-64, are registers rbp, rbx, and r12-15 callee safe or caller safe?

Answer 13

Callee safe.

They must be returned to their previous values by the caller before the function returns.

Question 14

In C calling conventions for x86-64, which register is used to hold the first 64 bits of a return value?

Answer 14

rax

Question 15

In C calling conventions for x86-64, which register is used to hold the second 64 bits of a 128 bit return value?

Answer 15

rdx