32-Bit Linux Assembly: Ep.2 – New Sections and File Manipulation

Question 1

What are the three main types of operands?

Answer 1

Register operand

Memory operand

Immediate operand

Question 2

What does [eax] mean?

Answer 2

Square brackets indicate “the value located at”, so [eax] would mean “the value contained in eax”

Question 3

value = 0x00408000

0x00408000 contains “0x54”

If the instruction “mov ebx, [value]” is issued, what will the value entered into the ebx register be?

Answer 3

0x54.

Question 4

What does 70q mean in assembly?

Answer 4

70 in “Octal” notation.

Question 5

What does 20o mean in assembly?

Answer 5

20 in “Octal” notation.

Question 6

What does 0b10011000 mean in assembly?

Answer 6

10011000 in binary notation.

Question 7

What is .bss short for?

Answer 7

Block Started by Symbol (BSS).

Question 8

What is stored in the .bss section?

Answer 8

Uninitialised variables.

Question 9

What permissions should the .bss section have?

Answer 9

Writeable but not executable.

Question 10

What permissions should the .data section have?

Answer 10

Writeable but not executable.

Question 11

What does the .bss section in an object file contain?

Answer 11

The .bss section stores the length of the units of data that are to be stored there.

Question 12

What happens to the .bss section when the executable is loaded into memory?

Answer 12

The operating system allocates the amount of memory dictated by the .bss section, to store the uninitialised variables in.

Question 13

What does resw 2, in assembly mean?

Answer 13

“Reserve” 2 words: 2x 16-bit variables worth of space.

Question 14

How would you reserve 2 bytes of memory using assembly?

Answer 14

resb 2

Question 15

How would you reserve 3x32-bits of memory using assembly?

Answer 15

resd 3

Question 16

Where are uninitialised variables stored?

Answer 16

The .bss section.

Question 17

Where are initialised variables stored?

Answer 17

The .data section.

Question 18

What advantage does storing uninitialised variables in the .bss section provide?

Answer 18

Disk space is saved when the executable is not loaded into memory, as only the length of an uninitialised variable is stored in the executable.

Question 19

What does resd stand for?

Answer 19

Reserve dword.

Question 20

What does resw stand for?

Answer 20

Reserve word.

Question 21

How many bits of memory would be reserved by the following line of assembly?

resw 6 ;

Answer 21

6 words = 6x16 bits = 96 bits

Question 22

How many bits of memory would be reserved by the following line of assembly?

resd 6 ;

Answer 22

6 d-words = 6x32 = 192 bits

Question 23

How many bits of memory would be reserved by the following line of assembly?

resb 6 ;

Answer 23

6 bytes = 6x8 bits = 48 bits

Question 24

How many bits of memory would be reserved by the following line of assembly?

resd 2 ;

Answer 24

2 d-words = 2x32 = 64 bits

Question 25

How many bits of memory would be reserved by the following line of assembly?

resw 3 ;

Answer 25

3 words 3x16 = 48 bits

Question 26

Which syscall is 3 in x86?

Answer 26

sys_read

Question 27

What is the call number for the sys_read syscall?

Answer 27

3

Question 28

How would you execute a sys_read call in x86 assembly?

Answer 28

mov eax, 3 ;

Question 29

Name one type of operand

Answer 29

The three types are:

• Register operand
• Memory operand
• Immediate operand

Question 30

What is the third type of operand?

• …
• Register operand
• Memory operand

Answer 30

Immediate operand

Question 31

What is the third type of operand?

• …
• Immediate operand
• Register operand

Answer 31

Memory operand

Question 32

What is the third type of operand?

• …
• Immediate operand
• Memory operand

Answer 32

Register operand

Question 33

What is syscall 8?

Answer 33

sys_create

Question 34

What is the syscall number for sys_open in 32-bit x86?

Answer 34

5

Question 35

What is syscall 6 in 32-bit x86?

Answer 35

sys_close

Question 36

value = 0x00408000

0x00408000 contains “0x54”

If the instruction “mov ebx, value” is issued, what will the value entered into the ebx register be?

Answer 36

0x00408000