Assembly Language Quiz: Master Instructions and More

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Questions and Answers

What exceptional behavior does the 'movl' instruction exhibit when a register is used as the destination?

It ignores the source operand.

It sets the high-order 4 bytes of the register to 0. (correct)

It generates a 64-bit value for the register.

It interprets the source operand as a memory address.

In x86-64, what convention is followed regarding instructions that produce a 32-bit value for a register?

The low-order portion of the register is set to 0.

The register is cleared.

The register is left unaffected.

The high-order portion of the register is set to 0. (correct)

What is the purpose of the 'movabsq' instruction in dealing with immediate data?

To work with floating-point numbers

To perform arithmetic operations

To handle arbitrary 64-bit immediate values (correct)

To move data between memory locations

What type of source operands can the regular 'movq' instruction accept?

32-bit two’s-complement numbers Signup and view all the answers

What do Figures 3.5 and 3.6 document regarding data movement instructions?

Instructions for copying smaller source values to larger destinations Signup and view all the answers

What does the 'mov' instruction convention dictate regarding the order of source and destination operands?

Source operand first, destination second Signup and view all the answers

What is the purpose of saving the argument rp in a different register (line 2) in the provided assembly code?

To store the remainder after division Signup and view all the answers

Which register is used to hold the quotient after the division operation in the provided assembly code?

%rax Signup and view all the answers

What type of division operation is performed in the assembly code?

Unsigned division Signup and view all the answers

Which instruction is used to sign-extend the dividend in the provided assembly code?

cqto Signup and view all the answers

What do lines 1 and 8 of the assembly code respectively accomplish?

Copy qp; return from function Signup and view all the answers

What should %rdx be set to before performing an unsigned division?

+0 Signup and view all the answers

What type of operand denotes the contents of a register?

Register Signup and view all the answers

Which component is part of a memory reference operand?

Effective address Signup and view all the answers

What is used to denote a reference to a value stored in memory starting at a specific address?

Mb[Addr] Signup and view all the answers

Which type of reference is often used when addressing elements of arrays?

General form syntax Signup and view all the answers

How is the effective address computed in a general memory reference?

$Imm + R[rb] + R[ri].s$ Signup and view all the answers

What is the most general form of memory reference shown in the text?

$Imm(rb, ri, s)$ Signup and view all the answers

Which instruction uses register %eax as its source and %rax as the destination for the sign-extended result?

mov %eax, (%rsp) Signup and view all the answers

What does the instruction movsbq %dl,%rax do?

Move the low-order byte of %rdx to the low-order byte of %rax Signup and view all the answers

In the context of data movement instructions, what is achieved by using movb %dl,%al?

Moving the low-order byte of %dl to the low-order byte of %al Signup and view all the answers

Which of the following instructions does not change the high-order bytes of the destination?

movb $0xAA, %dl Signup and view all the answers

What is the difference between movb and movzbq instructions?

movb only affects 8 bits while movzbq extends to 64 bits Signup and view all the answers

What is the purpose of the instruction movabsq $0x0011223344556677, %rax?

Move a 64-bit constant to register %rax Signup and view all the answers

Based on the text, what is the main advantage of using conditional moves in code execution?

Conditional moves ensure the pipeline is always full Signup and view all the answers

In the context of code execution, what does 'TMP' represent?

Time penalty for branch misprediction Signup and view all the answers

What is the relationship between 'TOK' and 'Tran' in the context of code execution?

'TOK' is the time to execute the code, and 'Tran' is the average time at p = 0.5 Signup and view all the answers

Why does code compiled using conditional moves take around 8 clock cycles regardless of the data being tested?

Conditional moves do not depend on data, ensuring constant timing Signup and view all the answers

When the branching pattern was random, the code required around 45 cycles. What can be inferred about branch prediction in this scenario?

Branch prediction was ineffective Signup and view all the answers

For TOK = 8 and Tran = 17.5, what would be the approximate miss penalty calculated based on the equation provided?

$24$ Signup and view all the answers

Study Notes

Data Movement Instructions

The 'movl' instruction exhibits exceptional behavior when a register is used as the destination, as it zero-extends the register to 64 bits.
In x86-64, instructions that produce a 32-bit value for a register follow the convention of zero-extending the result to 64 bits.

'movabsq' Instruction

The 'movabsq' instruction is used to handle immediate data, allowing for 64-bit immediate values to be moved into a register.

'movq' Instruction

The regular 'movq' instruction can accept various source operands, including registers, memory locations, and immediate values.

Data Movement Instructions (Figures 3.5 and 3.6)

Figures 3.5 and 3.6 document the different types of data movement instructions, including mov, movz, and movs.

'mov' Instruction Convention

The 'mov' instruction convention dictates that the source operand comes first, followed by the destination operand.

Assembly Code Analysis

In the provided assembly code, the argument rp is saved in a different register (line 2) to preserve the original value.
The register %rax is used to hold the quotient after the division operation.
The assembly code performs a signed division operation.
The 'cqo' instruction is used to sign-extend the dividend in the provided assembly code.
Lines 1 and 8 of the assembly code respectively accomplish setting up the dividend and storing the result.
Before performing an unsigned division, %rdx should be set to 0.

Operand Types

A register operand denotes the contents of a register.
A memory reference operand consists of a base register, index register, scale factor, and displacement.
An address operand is used to reference a value stored in memory starting at a specific address.
A scaled indexed address is often used when addressing elements of arrays.
The effective address in a general memory reference is computed as: address = base + index * scale + displacement.

Sign-Extension and Zero-Extension

The 'movs' instruction sign-extends the source operand to the destination register.
The 'movz' instruction zero-extends the source operand to the destination register.
The 'movsbq' instruction sign-extends the 8-bit source operand to the 64-bit destination register.

Conditional Moves

Using conditional moves in code execution achieves faster performance and reduces branching.
In the context of code execution, 'TMP' represents a temporary value.
'TOK' and 'Tran' are related in the context of code execution, where TOK is the threshold and Tran is the transition time.
Code compiled using conditional moves takes around 8 clock cycles regardless of the data being tested because the branch predictor is not affected.
When the branching pattern is random, the code requires around 45 cycles, indicating poor branch prediction.
The approximate miss penalty can be calculated as TOK + Tran = 8 + 17.5 = 25.5.

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Test your knowledge of assembly language instructions by determining the appropriate instruction suffix based on the operands provided in each line of assembly language code. This quiz includes practice problems similar to the given example.

Assembly Language Instructions Quiz

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