CS208 Introduction to Computer Systems
Wednesday, 11 October 2023

+ Test
Possible: 43
Mean, median: about 30
Toughest page: 2
Meanest individual problem: 8


Opportunities to improve your understanding (and gain a few extra points)

- Redo the problems you didn't get full points for
    - open book, open internet
    - put your redone problems on separate paper, clearly labeled
    - staple your redone problems to your original exam
    - hand in by Wednesday, 10/18, 11:10 AM -- no exceptions
    - your exam score will be the average of your in-class score and your redo score
    - please focus on understanding rather than points; you'll be glad you did

- If there's interest, I can run a 90-minute review session
    Monday xor Tuesday. Only if you're interested in attending,
    please fill out the survey I linked on Slack #announcements

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+ Good alternative textbook: Dive Into Systems
- Ch 7, on x86_64: https://diveintosystems.org/book/C7-x86_64/index.html

+ Short list of key ideas (* for today)
* Instructions, operands, and naming suffixes
* Registers and their names
* Register conventional uses
* Instruction pointer (rip)
* EFLAGS register
- A handful of essential instructions
    * MOV
    ADD
    SUB
    * CMP
    * TEST
    * JMP and its many friends
    RET
    CALL
- Addressing modes
- The stack pointer (rsp)

+ Questions to learn the answers to
- At the moment I call a function (with the call instruction), where
    are the parameters stored?
+ Let's play with them
- Write a little code that




+ x86_64 assembly essentials
- General data registers (rax, rbx, rcx, rdx, rdi, rsi, r8, r9,...)

- Naming of parts of the registers
    rax = 64 bits (8 bytes)
    eax = lowest-order 32 bits (4 bytes) in rax
    ax = lowest-order 16 bits (2 bytes) in rax
    al = lowest-order 8 bits (1 byte) in rax

- Naming the instructions by size of operand
    movq: "quad word" - 64-bit operands
    movl: "long word" - 32-bit operands
    movb: "byte" - 8-bit operands

- Special registers
    rip - the instruction pointer (i.e., the address of the next instruction to be executed)
    eflags - the "condition codes" saving info about the most recent instruction
    rsp - the stack pointer

- Conventional roles for general registers
    rax/eax - return value goes here before ret
    rdi/edi - 1st parameter in function call
    rsi/esi - 2nd parameter
    rdx/edx - 3rd parameter
    rcx/ecx - 4th parameter
    r8/r8d - 5th parameter
    r9/r9d - 6th parameter
 
- Addressing modes
    immediate
    register
    ...