college/Fall-2024/CS-3843/Assignments/7/Assignment.typ

#show link: set text(blue)
#set text(font: "Calibri")
#show raw: set text(font: "Fira Code")
#set table.cell(breakable: false)
#set table(stroke: (x, y) => (
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    .1pt
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  top: if y == 1 {
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))

#set page(margin: (x: .25in, y: .25in))
#let solve(solution) = {
  block(
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    stroke: blue + .3pt,
    fill: rgb(0, 149, 255, 15%),
    radius: 4pt,
  )[#solution]
}

#let solvein(solution) = {
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  h(outset)
  box(
    outset: outset,
    stroke: blue + .3pt,
    fill: rgb(0, 149, 255, 15%),
    radius: 4pt,
  )[#solution]
}

#let note(content) = {
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}

#let notein(content) = {
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    stroke: luma(20%) + .3pt,
    fill: luma(95%),
    radius: 4pt,
  )[#content]
}

#align(center)[
  = CS 3843 Computer Organization
  HW 7\
  #underline[Price Hiller] *|* #underline[zfp106]
]
#line(length: 100%, stroke: .25pt)


1. (18 points) Show your work. Show how you compute memory addresses by using the effective memory address computation.

  Assume the following values are stored at the indicated memory addresses and registers:

  #table(
    inset: (
      x: 15pt,
    ),
    columns: (auto, auto, auto, auto),
    table.header(
      [Address],
      [Value],
      [Register],
      [Value],
    ),

    [`0x100`], [`0xFF`], [`%rax`], [`0x100`],
    [`0x104`], [`0xAB`], [`%rcx`], [`0x1`],
    [`0x108`], [`0x13`], [`%rdx`], [`0x3`],
    [`0x10C`], [`0x11`], [``], [``],
  )

  Fill in the following table showing the values for indicated operands:
  #table(
    inset: (
      x: 15pt,
    ),
    columns: (auto, auto, auto),
    table.header(
      [Operand],
      [Value],
      [Work],
    ),

    [`%rax`],
    solve[`0x100`],
    note[
      + `%rax`
      + `0x100`
    ],

    [`0x104`],
    solve[`0xAB`],
    note[
      + `0x104`
      + `0xAB`
    ],

    [`$0x108`],
    solve[`0x108`],
    note[
      + `$0x108`
      + `0x108`
    ],

    [`(%rax)`],
    solve[`0xFF`],
    note[
      + `(%rax)`
      + `(0x100)`
      + `0xFF`
    ],

    [`4(%rax)`],
    solve[`0xAB`],
    note[

      + `4(%rax)`
      + `(%rax + 4)`
      + `(0x100 + 4)`
      + `(0x104)`
      + `0xAB`
    ],

    [`9(%rax,%rdx)`],
    solve[`0x11`],
    note[
      + `9(%rax,%rdx)`
      + `(%rax + %rdx + 9)`
      + `(0x100 + 0x3 + 9)`
      + `(0x10C)`
      + `0x11`
    ],

    [`260(%rcx,%rdx)`],
    solve[`0x11`],
    note[
      + `260(%rcx,%rdx)`
      + `(%rcx + %rdx + 260)`
      + `(%rcx + %rdx + 0x104)`
      + `(0x1 + 0x3 + 0x104)`
      + `(0x108)`
      + `0x13`
    ],

    [`0xFC(,%rcx,4)`],
    solve[`0x104`],
    note[
      + `0xFC(,%rcx,4)`
      + `(%rcx * 4 + 0xFC)`
      + `(0x1 * 4 + 0xFC)`
      + `(0x4 + 0xFC)`
      + `(0x100)`
      + `0xFF`
    ],

    [`(%rax,%rdx,4)`],
    solve[`0x10C`],
    note[
      + `(%rax,%rdx,4)`
      + `(%rax + %rdx * 4)`
      + `(0x100 + 0x3 * 4)`
      + `(0x100 + 0xC)`
      + `(0x10C)`
      + `0x11`
    ],
  )

2. (12 points) Explain for each line why you chose a certain suffix such as `b`, `w`, `l`, or `q`.

  For each of the following lines of assembly language, determine the appropriate instruction suffix based on the operands. (For example `mov` can be written as `movb`, `movw`, `movl`, or `movq`.)

  #align(center)[#note[My reasoning? My reasoning is that ChatGPT said so. _Just kidding ;)_.]]

  #table(
    inset: (
      x: 15pt,
    ),
    columns: (auto, auto),
    table.header(
      [Line],
      [Reasoning],
    ),

    [`mov`#solvein[`l`] ` %eax, (%rsp)`],
    [#note[Because we're moving into a memory location pointed to by `%rsp`, we want to focus on the size of `%eax`. `%eax` is a 4 byte register, so we want an instruction that operates on double words, so our suffix will be an `l`.]],

    [`mov`#solvein[`w`] ` (%rax), %dx`],
    [#note[We're moving from a value pointed to by an 8 byte register into a 2 byte register. 2 bytes is a word, so we want to use a single word length instruction which is suffixed by a `w`.]],

    [`mov`#solvein[`b`] ` $0xFF, %bl`],
    [#note[Here we have a raw hex value representing a singe byte, `1111 1111`, and we're moving it into a single byte length register so we'll want to use a byte length instruction which is suffixed by a `b`.]],

    [`mov`#solvein[`b`] ` (%rsp,%rdx,4), %dl`],
    [#note[Importantly, we are moving a value into `%dl` which is a single byte length; therefore, we want to use a single byte length instruction which is suffixed by a `b`.]],

    [`mov`#solvein[`q`] ` (%rdx), %rax`],
    [#note[Since we're moving a value pointed to by an 8 byte register into an 8 byte register, we'll want to use a quad word length instruction which is suffixed by a `q`.]],

    [`mov`#solvein[`w`] ` %dx, (%rax)`],
    [#note[Because `(%rax)` is is a larger register than `%dx`, the only register that matters here is `%dx`. `%dx` can store 2 bytes which is a single word, so we should use a word length instruction, that begin suffixed by `w`.]],
  )

3. (14 points) Explain for answer for each line:

  Each of the following lines of code generates an error message when we invoke the assembler. Explain the what is wrong with each line.


  #table(
    inset: (
      x: 15pt,
    ),
    columns: (auto, auto),
    table.header(
      [Code],
      [Why it's wrong],
    ),

    [`movb $0xF, (%ebx)`],
    [#solve[This shouldn't be moving `$0xF` into the memory pointed to by `%ebx` as `(%ebx)` cannot be used as an address register in this context. Removing the parentheses would make it somewhat more valid.]],

    [`movl %rax, (%rsp)`],
    [#solve[The `l` suffix is intended to move 4 bytes, both `%rax` and `%rsp` are 8 bytes in size and thus `movl` is moving the wrong number of bytes.]],

    [`movw (%rax),4(%rsp)`],
    [#solve[Same issue as the previous one. The `w` suffix is intended to move 2 bytes, but both `%rax` and `%rsp` are 8 bytes in size and thus we have a operand size mismatch.]],

    [`movb %al,%sl`],
    [#solve[There is no such register `%sl`, there's `%si` or `%sil`, but not `%sl`.]],

    [`movq %rax,$0x123`],
    [#solve[We cannot have an *immediate* as a destination to move a value into.]],

    [`movl %eax,%rdx`],
    [#solve[Attempting to move a 4 byte value into an 8 byte register may lead to data loss. We should use an opcode that clears the upper bits of `%rdx`, like `movslq`.]],

    [`movb %si, 8(%rbp)`],
    [#solve[This is attempting to move a 2 byte value using a 1 byte opcode. Instead of `movb` we should use `movw`.]],
  )

4. (12 points) Show your work for each instruction. Show how you compute effective memory addresses.

  Assume the following values are stored at the indicated memory addresses and registers:
  #table(
    inset: (
      x: 15pt,
    ),
    columns: (auto, auto, auto, auto),
    table.header(
      [Address],
      [Value],
      [Register],
      [Value],
    ),

    [`0x100`], [`0xFF`], [`%rax`], [`0x100`],
    [`0x108`], [`0xAB`], [`%rcx`], [`0x1`],
    [`0x110`], [`0x13`], [`%rdx`], [`0x3`],
    [`0x118`], [`0x11`], [``], [``],
  )
  Fill in the following table showing the effects of the following instructions, in terms of both register or memory location what will be updated and the resulting value:

  #table(
    inset: (
      x: 15pt,
    ),
    columns: (auto, auto, auto, auto),
    table.header(
      [Instruction],
      [Destination],
      [Value],
      [Work],
    ),

    [`addq %rcx,(%rax)`],
    solve[`0x100`],
    solve[`0x100`],
    note[
      + `(%rax) = %rcx + (%rax)`
      + `(0x100) = 0x1 + (0x100)`
      + `(0x100) = 0x1 + 0xFF`
      + `(0x100) = 0x100`
    ],

    [`subq %rdx,8(%rax)`],
    solve[`0x108`],
    solve[`0xA8`],
    note[
      + `8(%rax) = 8(%rax) - %rdx`
      + `(0x100 + 8) = (0x100 + 8) - 0x3`
      + `(0x108) = (0x108) - 0x3`
      + `(0x108) = 0xAB - 0x3`
      + `(0x108) = 0xA8`
    ],

    [`imulq $16,(%rax,%rdx,8)`],
    solve[`0x118`],
    solve[`0x110`],
    note[
      + `(%rax,%rdx,8) = (%rax,%rdx,8) * 16`
      + `(0x100,0x3,8) = (0x100,0x3,8) * 16`
      + `(0x100 + 0x3 * 8) = (0x100 + 0x3 * 8) * 16`
      + `(0x100 + 0x18) = (0x100 + 0x18) * 16`
      + `(0x118) = (0x118) * 16`
      + `(0x118) = 0x11 * 16`
      + `(0x118) = 0x110`
    ],

    [`incq 16(%rax)`],
    solve[`0x110`],
    solve[`0x14`],
    note[
      + `16(%rax) = 16(%rax) + 1`
      + `16(0x100) = 16(0x100) + 1`
      + `(0x100 + 16) = (0x100 + 16) + 1`
      + `(0x110) = (0x110) + 1`
      + `(0x110) = 0x13 + 1`
      + `(0x110) = 0x14`
    ],

    [`decq %rcx`],
    solve[`%rcx`],
    solve[`0x0`],
    note[
      + `%rcx = %rcx - 1`
      + `%rcx = 0x1 - 1`
      + `%rcx = 0x0`
    ],

    [`subq %rdx,%rax`],
    solve[`%rax`],
    solve[`0xFD`],
    note[
      + `%rax = %rax - %rdx`
      + `%rax = 0x100 - 0x3`
      + `%rax = 0xFD`
    ],
  )