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Notes on frame pointers.

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Joshua Potter 2024-11-18 11:01:18 -07:00
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"Basic": [

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- [ ] Sheet Music (10 min.)
- [ ] Korean (Read 1 Story)
* Start adding notes on [[procedures]].
* Start adding notes on [[x86-64/procedures]].

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@ -7,3 +7,5 @@ title: "2024-11-18"
- [ ] OGS
- [ ] Sheet Music (10 min.)
- [ ] Korean (Read 1 Story)
* Notes on [[x86-64/procedures#Frame Pointer|frame pointers]].

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@ -40,7 +40,7 @@ END%%
### Arrays
An array is a contiguous sequence of objects. An array is either a **fixed-length array** (FLA) or a **variable-length array** (VLA).
An array is a contiguous sequence of objects. An array is either a **fixed-length array** or a **variable-length array**.
%%ANKI
Cloze
@ -155,114 +155,6 @@ Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co
<!--ID: 1727957575990-->
END%%
%%ANKI
Basic
Where *must* a VLA be declared?
Back: Within a function.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957575996-->
END%%
%%ANKI
Basic
What two ways can the length of an FLA be specified?
Back: By an ICE or an initializer.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957576002-->
END%%
%%ANKI
Basic
Is the following an FLA or VLA?
```c
double a[4];
```
Back: FLA.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957576008-->
END%%
%%ANKI
Basic
Is the following an FLA or VLA?
```c
double a[];
```
Back: N/A. This is invalid syntax.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957576013-->
END%%
%%ANKI
Basic
Is the following an FLA or VLA?
```c
double a[] = { 0 };
```
Back: FLA.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957576019-->
END%%
%%ANKI
Basic
Is the following an FLA or VLA?
```c
int n = 2;
double a[n];
```
Back: VLA.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957576025-->
END%%
%%ANKI
Basic
Is the following an FLA or VLA?
```c
#define n 2
double a[n];
```
Back: FLA.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957576030-->
END%%
%%ANKI
Basic
Is the following an FLA or VLA?
```c
enum { n = 2 };
double a[n];
```
Back: FLA.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957576036-->
END%%
%%ANKI
Basic
Is the following an FLA or VLA?
```c
int n = 2;
double a[n] = {0};
```
Back: N/A. This is an invalid assignment.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957576041-->
END%%
%%ANKI
Basic
For the following to be an FLA, what must `N` be?
```c
double a[N];
```
Back: An ICE.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957576047-->
END%%
%%ANKI
Basic
Replace `EXPR` in the following with an expression to compute the length of `A`.
@ -555,6 +447,165 @@ Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co
<!--ID: 1730758755493-->
END%%
%%ANKI
Basic
Is the following an FLA or VLA?
```c
double a[4];
```
Back: FLA.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957576008-->
END%%
%%ANKI
Basic
Is the following an FLA or VLA?
```c
double a[];
```
Back: N/A. This is invalid syntax.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957576013-->
END%%
%%ANKI
Basic
Is the following an FLA or VLA?
```c
double a[] = { 0 };
```
Back: FLA.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957576019-->
END%%
%%ANKI
Basic
Is the following an FLA or VLA?
```c
int n = 2;
double a[n];
```
Back: VLA.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957576025-->
END%%
%%ANKI
Basic
Is the following an FLA or VLA?
```c
#define n 2
double a[n];
```
Back: FLA.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957576030-->
END%%
%%ANKI
Basic
Is the following an FLA or VLA?
```c
enum { n = 2 };
double a[n];
```
Back: FLA.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957576036-->
END%%
%%ANKI
Basic
Is the following an FLA or VLA?
```c
int n = 2;
double a[n] = {0};
```
Back: N/A. This is an invalid assignment.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957576041-->
END%%
#### Fixed-Length
A fixed-length array (FLA) has a predetermined size. Their stack allocations can be computed at compilation time.
%%ANKI
Basic
What is FLA an acronym for?
Back: **F**ixed-**l**ength **a**rray.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634166-->
END%%
%%ANKI
Basic
What two ways can the length of an FLA be specified?
Back: By an ICE or an initializer.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957576002-->
END%%
%%ANKI
Basic
For the following to be an FLA, what must `N` be?
```c
double a[N];
```
Back: An ICE.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957576047-->
END%%
%%ANKI
Basic
*Why* must FLAs be declared within a function?
Back: N/A. They can exist elsewhere.
Tags: x86-64
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634167-->
END%%
#### Variable-Length
A variable-length array (VLA) has its size determined at runtime. Their stack allocations must be determined with respect to other registers available to the frame.
%%ANKI
Basic
What is VLA an acronym for?
Back: **V**ariable-**l**ength **a**rray.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634168-->
END%%
%%ANKI
Basic
Where *must* a VLA be declared?
Back: Within a function.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1727957575996-->
END%%
%%ANKI
Basic
*Why* do variable-length arrays require use of a frame pointer?
Back: Offsets depend on how much space must be allocated on the stack.
Tags: x86-64
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634169-->
END%%
%%ANKI
Basic
*Why* must VLAs be declared within a function?
Back: Their implementation relies on frame pointers.
Tags: x86-64
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634170-->
END%%
### Structures
A `struct` is a grouping of data together. It has the following general form:

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@ -320,10 +320,7 @@ END%%
%%ANKI
Basic
What equivalent no-operand instruction does x86-64 provide?
```asm
movslq %eax, %rax
```
How is `movslq %eax, %rax` equivalently written using a single no-operand instruction?
Back: `cltq`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728382784107-->
@ -331,10 +328,7 @@ END%%
%%ANKI
Basic
What equivalent no-operand instruction does x86-64 provide?
```asm
movzlq %eax, %rax
```
How is `movzlq %eax, %rax` equivalently written using a single no-operand instruction?
Back: N/A.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728479148446-->
@ -396,8 +390,8 @@ Basic
How is `pushq %rbp` equivalently written using a pair of instructions?
Back:
```asm
subq $8,%rsp
movq %rbp,(%rsp)
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-->
@ -408,8 +402,8 @@ Basic
How is `popq %rax` equivalently written using a pair of instructions?
Back:
```asm
movq (%rsp),%rax
addq $8,%rsp
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-->
@ -448,8 +442,12 @@ END%%
%%ANKI
Basic
What is the `%rsp` register typically used for?
Back: The stack pointer.
Why is register `%rsp` named the way it is?
Back: It stands for **s**tack **p**ointer.
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%%
## Bibliography
* Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.

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@ -6,7 +6,7 @@ tags:
- x86-64
---
### Load Effective Address
### LEAQ
| Instruction | Operands | Effect | Description |
| ----------- | -------- | ------- | ---------------------- |
@ -237,7 +237,7 @@ END%%
%%ANKI
Basic
Which `SUB` instruction is equivalent to `decq %rcx`?
How is `decq %rcx` equivalently written using the `SUB` instruction class?
Back:
```asm
subq $1, %rcx

8
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@ -8,10 +8,10 @@ tags:
### Unary Operations
| Instruction | Operands | Effect | Description |
| ----------- | -------- | ---------- | ----------- |
| `neg[bwlq]` | D | D <- -D | Negate |
| `not[bwlq]` | D | D <- ~D | Complement |
| Instruction | Operands | Effect | Description |
| ----------- | -------- | ------- | ----------- |
| `neg[bwlq]` | D | D <- -D | Negate |
| `not[bwlq]` | D | D <- ~D | Complement |
%%ANKI
Basic

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@ -0,0 +1,169 @@
---
title: Procedures
TARGET DECK: Obsidian::STEM
FILE TAGS: x86-64
tags:
- x86-64
---
## Overview
The details of procedures are detailed in [[x86-64/procedures|procedures]]. This file touches on the most relevant instruction classes.
## CALL and RET
Like [[conditions#JMP|JMP]] instructions, `call` allows specifying a direct or indirect operand. `call` pushes the address of the instruction following it onto the stack and updates the PC to the operand. `ret` reverts these steps.
| Instruction | Operands | Description |
| ----------- | ----------- | ---------------- |
| `call` | Label | Procedure call |
| `call` | \**Operand* | Procedure call |
| `ret` | | Return from call |
%%ANKI
Cloze
The {`call`} instruction is the counterpart to the {`ret`} instruction.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728558288130-->
END%%
%%ANKI
Basic
What two things does the `call` instruction do?
Back: It pushes the return address on the stack and updates the PC.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728558288148-->
END%%
%%ANKI
Basic
What two things does the `ret` instruction do?
Back: It pops the return address off the stack and updates the PC.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728558288160-->
END%%
%%ANKI
Basic
How is `ret` equivalently written using a line of assembly?
Back:
```asm
popq %rip
```
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634162-->
END%%
%%ANKI
Basic
The operand forms of `call` mirror what other instruction class?
Back: `JMP`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728558288165-->
END%%
%%ANKI
Basic
A `call` instruction pushes what address onto the stack?
Back: That of the instruction following the `call` instruction.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728558288171-->
END%%
%%ANKI
Basic
What return address is pushed onto the stack after `call` is run?
```x86
1: ...
2: callq .L1
3: ...
```
Back: `3`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728558288177-->
END%%
%%ANKI
Basic
What address is the PC updated to after `call` is run?
```x86
1: ...
2: callq .L1
3: ...
```
Back: That corresponding to label `.L1`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728558288183-->
END%%
%%ANKI
Basic
Which register(s) does a `call` instruction update?
Back: `%rsp` and `%rip`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728559336730-->
END%%
%%ANKI
Basic
Which register(s) does a `ret` instruction update?
Back: `%rsp` and `%rip`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728559336760-->
END%%
## LEAVE
`leave` parallels the `ret` instruction. It is equivalent to the following two instructions:
```asm
movq %rbp, %rsp
popq %rbp
```
%%ANKI
Basic
What two things does the `leave` instruction do?
Back: Restores the stack pointer and pops off the caller-saved base pointer.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634163-->
END%%
%%ANKI
Basic
How is `leave` equivalently written using a pair of instructions?
Back:
```asm
movq %rbp, %rsp
popq %rbp
```
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634164-->
END%%
%%ANKI
Basic
Fixed-sized frames use which of `leave` and/or `ret`?
Back: Just `ret`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952715097-->
END%%
%%ANKI
Basic
Variable-sized frames use which of `leave` and/or `ret`?
Back: Bot
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952715103-->
END%%
%%ANKI
Cloze
{1:`ret`} is to {2:`%rsp`} whereas {2:`leave`} is to {1:`%rbp`}.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634165-->
END%%
## Bibliography
* Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.

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@ -134,100 +134,7 @@ Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Program
<!--ID: 1730121604407-->
END%%
## CALL and RET
Like [[conditions#JMP|JMP]] instructions, `call` allows specifying a direct or indirect operand. `call` pushes the address of the instruction following it onto the stack and updates the PC to the operand. `ret` reverts these steps.
| Instruction | Operands | Description |
| ----------- | ----------- | ---------------- |
| `call` | Label | Procedure call |
| `call` | \**Operand* | Procedure call |
| `ret` | | Return from call |
%%ANKI
Cloze
The {`call`} instruction is the counterpart to the {`ret`} instruction.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728558288130-->
END%%
%%ANKI
Basic
What two things does the `call` instruction do?
Back: It pushes the return address on the stack and updates the PC.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728558288148-->
END%%
%%ANKI
Basic
What two things does the `ret` instruction do?
Back: It pops the return address off the stack and updates the PC.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728558288160-->
END%%
%%ANKI
Basic
The operand forms of `call` mirror what other instruction class?
Back: `JMP`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728558288165-->
END%%
%%ANKI
Basic
A `call` instruction pushes what address onto the stack?
Back: That of the instruction following the `call` instruction.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728558288171-->
END%%
%%ANKI
Basic
What return address is pushed onto the stack after `call` is run?
```x86
1: ...
2: callq .L1
3: ...
```
Back: `3`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728558288177-->
END%%
%%ANKI
Basic
What address is the PC updated to after `call` is run?
```x86
1: ...
2: callq .L1
3: ...
```
Back: That corresponding to label `.L1`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728558288183-->
END%%
%%ANKI
Basic
Which register(s) does a `call` instruction update?
Back: `%rsp` and `%rip`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728559336730-->
END%%
%%ANKI
Basic
Which register(s) does a `ret` instruction update?
Back: `%rsp` and `%rip`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1728559336760-->
END%%
## Local Storage
### On the Stack
## Local Variables
x86-64 employs 6 registers for passing integral (i.e. integer and pointer) arguments between caller and callee.
@ -633,7 +540,7 @@ Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Program
<!--ID: 1730120207052-->
END%%
### In Registers
## Callee-Saved Registers
x86-64 employs 6 registers as callee-saved registers. If procedure `P` calls procedure `Q`, `Q` *must* preserve the values of these registers. That is, if `Q` were to modify these registers, `Q` is also responsible for restoring these values before returning back to `P`.
@ -660,6 +567,14 @@ Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Program
<!--ID: 1730121604414-->
END%%
%%ANKI
Basic
Which registers are designated as caller-saved?
Back: All but callee-saved registers and `%rsp`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731946757133-->
END%%
%%ANKI
Basic
*What* is a callee-saved register?
@ -691,6 +606,153 @@ Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Program
<!--ID: 1730121604434-->
END%%
%%ANKI
Basic
Which number-suffixed register(s) are used for passing integral arguments to procedures?
Back: `%r8` and `%r9`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731938810848-->
END%%
%%ANKI
Basic
Which number-suffixed register(s) are conventionally designated "callee-saved"?
Back: `%r12`, `%13`, `%r14`, and `%r15`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731938810852-->
END%%
%%ANKI
Basic
Which number-suffixed register(s) are conventionally designated "caller-saved"?
Back: `%r10` and `%r11`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731938810854-->
END%%
%%ANKI
Basic
What does it mean for a register to be callee-saved?
Back: The callee must ensure the register's value is unchanged by the time it returns.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731938810857-->
END%%
%%ANKI
Basic
What does it mean for a register to be caller-saved?
Back: Any procedure can modify the register's value.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731938810860-->
END%%
%%ANKI
Basic
*Why* are caller-saved registers named the way they are?
Back: It's up to the caller to preserve their value before a procedure call.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731938810863-->
END%%
%%ANKI
Basic
What misnomer does designating `%r10` and `%r11` as caller-saved registers introduce?
Back: This seems to imply there are no other caller-saved registers.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731946757135-->
END%%
## Frame Pointer
The **frame pointer**, also known as the **base pointer**, marks the start of a variable-sized frame. `%rbp` is pushed onto the stack (since it is caller-saved) and its value updated to the new value of `%rsp`. Relative offsets are then computed according to it.
%%ANKI
Basic
Why is register `%rbp` named the way it is?
Back: It stands for **b**ase **p**ointer.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634150-->
END%%
%%ANKI
Cloze
{1:`%rsp`} is to {2:fixed}-sized frames whereas {2:`%rbp`} is to {1:variable}-sized frames.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634151-->
END%%
%%ANKI
Basic
When is the `%rbp` register used?
Back: When working with variable-sized frames.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634153-->
END%%
%%ANKI
Basic
In fixed-sized frames, what is the first callee-saved register on the stack?
Back: Indeterminate.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634154-->
END%%
%%ANKI
Basic
In variable-sized frames, what is the first callee-saved register on the stack?
Back: `%rbp`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634155-->
END%%
%%ANKI
Basic
What is typically the ultimate instruction of a fixed-sized frame?
Back: `ret`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634156-->
END%%
%%ANKI
Basic
What is typically the penultimate instruction of a fixed-sized frame?
Back: Indeterminate.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634157-->
END%%
%%ANKI
Basic
What is typically the ultimate instruction of a variable-sized frame?
Back: `ret`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634158-->
END%%
%%ANKI
Basic
What is typically the penultimate instruction of a variable-sized frame?
Back: `leave`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634159-->
END%%
%%ANKI
Basic
Assume frame `Q` starts at address `S`. If applicable, what address is its frame pointer set to?
Back: `S + 8`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634160-->
END%%
%%ANKI
Basic
Assume frame `Q` starts at address `S`. When applicable, *why* is `%rbp` set to `S + 8`?
Back: It's the value of `%rsp` after pushing the previous value of `%rbp`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731952634161-->
END%%
## Bibliography
* Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.

46
notes/x86-64/registers.md
View File

@ -309,50 +309,10 @@ END%%
%%ANKI
Basic
Which number-suffixed register(s) are used for passing integral arguments to procedures?
Back: `%r8` and `%r9`.
What misnomer does designating registers for a certain purpose introduce?
Back: Designations are convention-based. Registers can be used for any purpose.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731938810848-->
END%%
%%ANKI
Basic
Which number-suffixed register(s) are conventionally designated "callee-saved"?
Back: `%r12`, `%13`, `%r14`, and `%r15`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731938810852-->
END%%
%%ANKI
Basic
Which number-suffixed register(s) are conventionally designated "caller-saved"?
Back: `%r10` and `%r11`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731938810854-->
END%%
%%ANKI
Basic
What does it mean for a register to be callee-saved?
Back: The callee must ensure the register's value is unchanged by the time it returns.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731938810857-->
END%%
%%ANKI
Basic
What does it mean for a register to be caller-saved?
Back: Any procedure can modify the register's value.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731938810860-->
END%%
%%ANKI
Basic
*Why* are caller-saved registers named the way they are?
Back: It's up to the caller to preserve their value before a procedure call.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731938810863-->
<!--ID: 1731946757131-->
END%%
## Condition Codes