Diving into Assembly: Basics

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Section 7.1 Diving into Assembly: Basics

Checkpoint 7.1.1. Examining Components of Assembly Code (objdump output).

Given the following line of output from objdump:

40052d: 8b 45 fc mov -0x4(%rbp),%eax

Match each component with its corresponding identifier:

Review Ch. 7.1 - Assembly Basics

¹

diveintosystems.org/book/C7-x86_64/basics.html

mov
Instruction Name
0x40052d
Instruction Address
8b45fc
Machine Code Representation of Instruction
-0x4(%rbp), %eax
Instruction Operands

Checkpoint 7.1.2. Relationship Between C Code and Assembly Code.

Which of the following statements is true about the relationship between a single line of C code and assembly code?

One line of C code always translates into exactly one assembly instruction.
Incorrect.
One line of C code often translates into one or more assembly instructions.
Correct!
One line of C code always translates into two or more assembly instructions.
close, but incorrect!
There is no relationship between C code and assembly code.
Incorrect.

Checkpoint 7.1.3. General-Purpose Registers.

Which of the following x86-64 registers are general purpose?

%rax
Correct!
%rsi
Correct!
%rip
Incorrect. %rip is the instruction pointer. It cannot be directly written to.
%r8
Correct!

Checkpoint 7.1.4. Special Use Cases for Registers.

Some registers are typically used for special purposes. Match the following registers with a typical defined use case for that register.

Review Ch. 7.1.1 - Registers

²

diveintosystems.org/book/C7-x86_64/basics.html#_registers

%rsp
Pointer to the top of the stack
%rip
Pointer to the next instruction to execute
%rax
General-purpose register
%rbp
Pointer to the bottom of the active stack

Answer.

Did you know? Register x0 is also used to hold the return value of a function!

Checkpoint 7.1.5. Registers - Capacity.

Order the following registers from smallest to largest capacity.

%al
---
%r8w
---
%ebx
---
%r13

Checkpoint 7.1.6. Identifying Operand Types.

For each of the following operands, label it as a (C)onstant, (R)egister, or (M)emory operand.

%rax
(%rax)
(%rax, %rbx, 4)
$0x5
0x5
$8

Hint.

Just enter the letter as your answer (one of C, R, or M)

Checkpoint 7.1.7. Identifying Operand Types.

The following tables provide the contents of several registers and memory locations.

Address	Value
0xFA00	0x5F
0xFA08	0x16
0xFA10	0x42
0xFA18	0x9C

Register	Value
%rax	0xFA08
%rdx	0x2

For each of the following operands, determine the associated value in hex.

%rax
%rdx
(%rax)
(%rax, %rdx, 4)
-0x8(%rax)
(%rax, %rdx, 8)

Hint.

Remember to include the 0x prefix in your answers.