407 lines
15 KiB
Markdown
407 lines
15 KiB
Markdown
---
|
|
title: Memory Access
|
|
TARGET DECK: Obsidian::STEM
|
|
FILE TAGS: x86-64
|
|
tags:
|
|
- x86-64
|
|
---
|
|
|
|
## MOV
|
|
|
|
The MOV instruction class has four primary variants: `movb`, `movw`, `movl`, and `movq`. There also exist zero extension and sign extension variations in the forms of MOVS and MOVZ.
|
|
|
|
| Instruction | Operands | Effect | Description |
|
|
| ------------ | -------- | ---------------- | ------------------------------------ |
|
|
| `mov[bwlq]` | S, D | D <- S | Move byte/word/double word/quad word |
|
|
| `movabsq` | I, R | R <- I | Move quad word |
|
|
| `movzb[wlq]` | S, R | R <- ZE(S) | Move zero-extended byte |
|
|
| `movzw[lq]` | S, R | R <- ZE(S) | Move zero-extended word |
|
|
| `movsb[wlq]` | S, R | R <- SE(S) | Move sign-extended byte |
|
|
| `movsw[lq]` | S, R | R <- SE(S) | Move sign-extended word |
|
|
| `movslq` | S, R | R <- SE(S) | Move sign-extended double word |
|
|
| `cltq` | | %rax <- SE(%eax) | Sign-extend `%eax` to `%rax` |
|
|
|
|
Notice there is no `movzlq` instruction. `movl` covers this functionality since, by convention, instructions moving double words into a 64-bit register automatically zeroes out the upper 32 bits.
|
|
|
|
%%ANKI
|
|
Basic
|
|
What four variants does `MOV` instructions take on in x86-64?
|
|
Back: `movb`, `movw`, `movl`, `movq`
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933397-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
How many bytes does a `movb` instruction operate on?
|
|
Back: One.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933403-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
How many bytes does a `movw` instruction operate on?
|
|
Back: Two.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933406-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
How many bytes does a `movl` instruction operate on?
|
|
Back: Four.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933409-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
How many bytes does a `movq` instruction operate on?
|
|
Back: Eight.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933413-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What combination of source and destination types is prohibited in `MOV` instructions?
|
|
Back: A source and destination memory address.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933416-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What is the result of `%rax` after instruction `movl $0x4050,%eax`?
|
|
Back: Upper 32-bits is `0` and lower 32-bits is `0x4050`.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933419-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What is the result of `%rax` after instruction `movq $0x4050,%rax`?
|
|
Back: The 64-bit value is `0x4050`.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933423-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What is the result of `%rax` after instruction `movw $0x4050,%ax`?
|
|
Back: The upper 48 bits are unchanged and the lower 16 bits are `0x4050`.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933426-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What is the result of `%rax` after instruction `movb $0x4050,%al`?
|
|
Back: The upper 56 bits are unchanged and the lower 8 bits are `0x50`.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933430-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What is the result of `%rax` after instruction `movw $0x4050,%al`?
|
|
Back: N/A. Invalid operand for instruction.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933433-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What caveat is applied to the source operand of `movq`?
|
|
Back: Immediates are 32-bit two's-complement numbers sign extended to 64-bits.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933437-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What `mov` instruction is needed when working with 64-bit immediate sources?
|
|
Back: `movabsq`
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933441-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What purpose does `movabsq` solve that `movq` does not?
|
|
Back: `movabsq` can have an arbitrary 64-bit immediate source.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933448-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What is the result of `%rax` after the following instructions?
|
|
```asm
|
|
movabsq $0x0011223344556677, %rax
|
|
movb $-1, %al
|
|
```
|
|
Back: `0x00112233445566FF`
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933452-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What is the result of `%rax` after the following instructions?
|
|
```asm
|
|
movabsq $0x0011223344556677, %rax
|
|
movw $-1, %ax
|
|
```
|
|
Back: `0x001122334455FFFF`
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933455-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What is the result of `%rax` after the following instructions?
|
|
```asm
|
|
movabsq $0x0011223344556677, %rax
|
|
movl $-1, %eax
|
|
```
|
|
Back: `0x00000000FFFFFFFF`
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933458-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What is the result of `%rax` after the following instructions?
|
|
```asm
|
|
movabsq $0x0011223344556677, %rax
|
|
movq $-1, %rax
|
|
```
|
|
Back: `0xFFFFFFFFFFFFFFFF`
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933461-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What is the `MOVZ` instruction class?
|
|
Back: `MOV` instructions that zero extend the source to fit into the destination.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933464-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What is the `MOVS` instruction class?
|
|
Back: `MOV` instructions that sign extend the source to fit into the destination.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933466-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What does the `movzbw` instruction do?
|
|
Back: Moves a zero-extended byte to a word.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933469-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What does the `movslq` instruction do?
|
|
Back: Moves a sign-extended double word to a quad word.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933472-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What does the `movslb` instruction do?
|
|
Back: N/A. This instruction does not exist.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933475-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What combinatorial argument explains the number of `MOVS` instructions?
|
|
Back: There exists an instruction for each smaller declaration to larger declaration.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933478-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What `MOVZ` instruction is "missing"?
|
|
Back: `movzlq`
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933481-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
Why does there not exist a `movzlq` instruction?
|
|
Back: Because `movl` already zeroes out the upper bits of a destination register.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933483-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What is the result of `%rax` after the following instructions?
|
|
```asm
|
|
movabsq $0x0011223344556677, %rax
|
|
movb $0xAA, %dl
|
|
movb %dl,%al
|
|
```
|
|
Back: `0x00112233445566AA`
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933486-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What is the result of `%rax` after the following instructions?
|
|
```asm
|
|
movabsq $0x0011223344556677, %rax
|
|
movb $0xAA, %dl
|
|
movsbq %dl,%rax
|
|
```
|
|
Back: `0xFFFFFFFFFFFFFFAA`
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933489-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What is the result of `%rax` after the following instructions?
|
|
```asm
|
|
movabsq $0x0011223344556677, %rax
|
|
movb $0xAA, %dl
|
|
movzbq %dl,%rax
|
|
```
|
|
Back: `0x00000000000000AA`
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1713625933491-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Cloze
|
|
A {pointer} in C is a {memory address} in x86.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
Tags: c17
|
|
<!--ID: 1714677608754-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
Dereferencing a pointer in C equates to what two operations in x86?
|
|
Back: Copying the pointer into a register and then using the register in a memory reference.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
Tags: c17
|
|
<!--ID: 1714677608758-->
|
|
END%%
|
|
|
|
## PUSH and POP
|
|
|
|
| Instruction | Operands | Effect | Description |
|
|
| ----------- | -------- | ------------------------------------------- | -------------- |
|
|
| `pushq` | S | R[%rsp] <- R[%rsp] - 8<br />M[R[%rsp]] <- S | Push quad word |
|
|
| `popq` | D | D <- M[R[%rsp]]<br />R[%rsp] <- R[%rsp] + 8 | Pop quad word |
|
|
|
|
In x86 processors, the stack grows downward, with the "top" of the stack corresponding to lower addresses.
|
|
|
|
%%ANKI
|
|
Basic
|
|
In what direction do x86-64 stacks grow?
|
|
Back: Downward.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1715377284944-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Cloze
|
|
The x86-64 stack grows such that the top element has the {lowest} address of all stack elements.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1715377284947-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What instruction is used to push elements onto the stack?
|
|
Back: `pushq`
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1715377284951-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What instruction is used to pop elements off of the stack?
|
|
Back: `popq`
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1715377284955-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
How is `pushq %rbp` equivalently written using a pair of instructions?
|
|
Back:
|
|
```asm
|
|
subq $8,%rsp
|
|
movq %rbp,(%rsp)
|
|
```
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1715377284959-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
How is `popq %rax` equivalently written using a pair of instructions?
|
|
Back:
|
|
```asm
|
|
movq (%rsp),%rax
|
|
addq $8,%rsp
|
|
```
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1715377284962-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Cloze
|
|
{1:`pushq`} is to {2:`subq`} as {2:`popq`} is to {1:`addq`}.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1715377284966-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
If `%rsp` has value `0x108`, what value does it have after a `pushq` instruction?
|
|
Back: `0x100`
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1715377284971-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
If `%rsp` has value `0x108`, what value does it have after a `popq` instruction?
|
|
Back: `0x110`
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1715377284975-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
Which register contains a pointer to the top of the stack?
|
|
Back: `%rsp`
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1715377284980-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What is the `%rsp` register typically used for?
|
|
Back: The stack pointer.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1715377284985-->
|
|
END%% |