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08-assembly-32bit.html
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<!doctype html>
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<title>CS 2150: 08-x86 (32 bit) slide set</title>
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<section data-markdown id="cover"><script type="text/template">
# CS 2150
### Program and Data Representation
<center><small>[Mark Floryan](http://www.cs.virginia.edu/~mrf8t) / [mrf8t@virginia.edu](mailto:mrf8t@virginia.edu)</small></center>
<center><small>Repository: [github.com/markfloryan/pdr](http://github.com/markfloryan/pdr) / [↑](index.html) / <a href="08-assembly-32bit.html?print-pdf"><img class="print" width="20" src="images/print-icon.png"></a></small></center>
## 32 bit x86 (assembly language)
</script></section>
<section>
<h2>CS 2150 Roadmap</h2>
<table class="wide">
<tr><td colspan="3"><p class="center">Data Representation</p></td><td></td><td colspan="3"><p class="center">Program Representation</p></td></tr>
<tr>
<td class="top"><small> <br> <br>string<br> <br> <br> <br>int x[3]<br> <br> <br> <br>char x<br> <br> <br> <br>0x9cd0f0ad<br> <br> <br> <br>01101011</small></td>
<!-- image adapted from http://openclipart.org/detail/3677/arrow-left-right-by-torfnase -->
<td><img class="noborder" src="images/red-double-arrow.png" height="500" alt="vertical red double arrow"></td>
<td class="top"> <br>Objects<br> <br>Arrays<br> <br>Primitive types<br> <br>Addresses<br> <br>bits</td>
<td> </td>
<td class="top"><small> <br> <br>Java code<br> <br> <br>C++ code<br> <br> <br>C code<br> <br> <br>x86 code<br> <br> <br>IBCM<br> <br> <br>hexadecimal</small></td>
<!-- image adapted from http://openclipart.org/detail/3677/arrow-left-right-by-torfnase -->
<td><img class="noborder" src="images/green-double-arrow.png" height="500" alt="vertical green double arrow"></td>
<td class="top"> <br>High-level language<br> <br>Low-level language<br> <br>Assembly language<br> <br>Machine code</td>
</tr>
</table>
</section>
<section data-markdown><script type="text/template">
# Contents
[Introduction to x86](#/introduction)
[x86 Instruction Set](#/x86insts)
[Calling Conventions](#/callingconv)
[Callee Rules](#/callee)
[Caller Rules](#/caller)
[Activation Records](#/actrecs)
[x86 Examples](#/examples)
</script></section>
<section>
<section id="introduction" data-markdown><script type="text/template">
# Introduction to x86
</script></section>
<section>
<h2>History of x86</h2>
<p><a href="https://en.wikipedia.org/wiki/File:C4004_%28Intel%29.jpg"><img alt="Intel 4004" src="images/08-x86/C4004.jpg"></a></p>
<table class="transparent"><tr><td>
<ul>
<li>1971: 4004, 4-bit words</li>
<li>1972: 8008, 8-bit words</li>
<li>1978: 8086, 16-bit words</li>
<li>1982: 80286</li>
<li>1985: 80386, 32-bit words</li>
<li>1989: 80486</li>
<li>1993: Pentium</li>
</ul>
</td><td>
<ul>
<li>1995: Pentium Pro</li>
<li>1997: Pentium II</li>
<li>1998: Pentium III</li>
<li>2000-2008: Pentium IV</li>
<li>2005-2008: Pentium D</li>
<li>2006-2011: Core 2</li>
<li>2008-present: Core i3, i5, i7</li>
</ul>
</td></tr></table>
</section>
<section data-markdown><script type="text/template">
## IBCM vs. x86: Registers
</script></section>
<section data-markdown><script type="text/template">
## IBCM vs. x86: Fetch Execute Cycle (same)
```
while(power is on) {
IR := mem[PC]
PC := PC + 1 (word) // 32-bits in x86
execute instruction in IR
}
```
- PC = program counter
- IR = instruction register
</script></section>
<section>
<h2>Declaring Variables in x86</h2>
<table class="transparent"><tr><td>
<p>Directives</p>
<ul>
<li>byte: 1 byte (DB) declare byte</li>
<li>word: 2 bytes (DW)</li>
<li>double: 4 bytes (DD)</li>
<li>quadword: 8 bytes (DQ)</li>
</ul>
<p> </p>
<p><code>TIMES x DB 0</code> directive means create x bytes of value zero</p>
</td><td>
<pre><code>section .data
a DB 23
b DW ?
c DD 3000
d DQ -800
x DD 1, 2, 3
y TIMES 8 DB 0
str DB 'hello', 0
z TIMES 50 DD ?</code></pre>
</td></tr></table>
</section>
<section data-markdown><script type="text/template">
## mov command
- `mov <dest>, <src>`
- Where dest and src can be:
- A register
- A constant
- Variable name
- Pointer: [ebx]
- (but with a few exceptions we'll see shortly)
</script></section>
<section>
<h2>Addressing Memory</h2>
<table class="transparent"><tr><td class="top">
<ul>
<li>Up to <i>2 registers</i> and one <i>32-bit signed constant</i> can be added together to compute a memory address<br> </li>
<li>Furthermore, one register can be pre-multiplied by 2, 4, or 8<ul>
<li>word-align</li>
<li>double-align</li>
<li>quadword-align</li>
</ul></li></ul>
</td><td style="width:50px"></td><td class="top">
<pre><code>mov eax, ebx
mov eax, [ebx]
mov [var], ebx
mov eax, [esi - 4]
mov [esi + eax], cl
mov edx, [esi + 4*ebx]</code></pre>
<p> </p>
<p>Incorrect: (why?)</p>
<pre><code>mov eax, [ebx - ecx]
mov [eax + esi + edi], ebx
mov [4*eax + 2*ebx], ecx</code></pre>
</td></tr></table>
</section>
<section>
<table class="transparent"><tr><td class="top">
<table class="transparent">
<tr><td class="top" colspan="3"><h2>Example</h2></td></tr>
<tr><td class="top"><p class="center">Source code:</p><pre><code>mov ecx, eax
mov edx, [ebx]
mov esi, [edx+eax+4]
mov [esi], 45
mov [a], 15
lea edi, [a]</code></pre></td>
<td style="width:50px"></td>
<td class="top">
<p class="center">Registers:</p>
<table class="transparent">
<tr><td>eax</td><td class="border" style="width:100px">100</td></tr>
<tr><td>ebx</td><td class="border" style="width:100px">104</td></tr>
<tr><td>ecx</td><td class="border" style="width:100px"><span class="fragment" data-fragment-index="1">100</span></td></tr>
<tr><td>edx</td><td class="border" style="width:100px"><span class="fragment" data-fragment-index="2">8</span></td></tr>
<tr><td>esi</td><td class="border" style="width:100px"><span class="fragment" data-fragment-index="3">200</span></td></tr>
<tr><td>edi</td><td class="border" style="width:100px;border-bottom:medium solid;"><span class="fragment" data-fragment-index="6">300</span></td></tr>
</table>
</td></tr></table>
</td><td style="width:50px"></td><td class="top">
<p class="center">Memory:</p>
<table class="transparent">
<tr><td>100</td><td class="border" style="width:100px"></td></tr>
<tr><td>104</td><td class="border" style="width:100px">8</td></tr>
<tr><td>108</td><td class="border" style="width:100px"></td></tr>
<tr><td>112</td><td class="border" style="width:100px">200</td></tr>
<tr><td>116</td><td class="border" style="width:100px"></td></tr>
<tr><td>...</td><td class="border" style="width:100px"></td></tr>
<tr><td>200</td><td class="border" style="width:100px"><span class="fragment" data-fragment-index="4">45</span></td></tr>
<tr><td>204</td><td class="border" style="width:100px"></td></tr>
<tr><td>...</td><td class="border" style="width:100px"></td></tr>
<tr><td>a: 300</td><td class="border" style="width:100px"><span class="fragment" data-fragment-index="5">15</span></td></tr>
<tr><td>304</td><td class="border" style="width:100px"></td></tr>
<tr><td>...</td><td class="border" style="width:100px;border-bottom:medium solid;"></td></tr>
</table>
</td></tr></table>
</section>
<section data-markdown><script type="text/template">
## `mov eax, [4*esi-edx]`
1. Valid
2. Invalid
3. Not sure
</script></section>
<section data-markdown><script type="text/template">
## `mov eax, [4*esi+4]`
1. Valid
2. Invalid
3. Not sure
</script></section>
<section data-markdown><script type="text/template">
## `mov eax, [4*esi+edx+8]`
1. Valid
2. Invalid
3. Not sure
</script></section>
<section data-markdown><script type="text/template">
## `mov eax, [esi+4*edx]`
1. Valid
2. Invalid
3. Not sure
</script></section>
<section data-markdown><script type="text/template">
## `mov eax+4, [esi]`
1. Valid
2. Invalid
3. Not sure
</script></section>
<section data-markdown><script type="text/template">
## Memory addressing restrictions
- The destination cannot be a constant (duh!)
- You cannot access memory twice in one instruction
- As the CPU does not have enough time to do so at that clock speed
- So the following instructions are invalid:
```
mov [eax], [var]
mov [eax+4], [ebx]
mov 20, [eax]
```
</script></section>
</section>
<section>
<section data-markdown id="x86insts"><script type="text/template">
# x86 Instruction Set
</script></section>
<section data-markdown><script type="text/template">
## x86 Instruction Set
- Data movement instructions
- Arithmetic instructions
- Logical instructions
- Control instructions
</script></section>
<section data-markdown><script type="text/template">
## Data Movement Instructions, part 1
- `mov`
- We've seen this in detail already
- `push`
- First decrements ESP (stack pointer) by 4 (stack grows ***down***)
- push (mov) operand onto stack (4 bytes)
```
push eax
push [var]
```
</script></section>
<section data-markdown><script type="text/template">
## Data Movement Instructions, part 2
- `pop`
- Pop top element of stack to memory or register, then increment stack pointer (ESP) by 4
- Value is written to the parameter
```
pop eax
pop [var]
```
- `lea`
- Load effective address
- Place address of second parameter into the first parameter
```
lea eax, [var]
lea edi, [ebx+4*esi]
```
</script></section>
<section data-markdown><script type="text/template">
## Arithmetic Instructions, part 1
- `add`, `sub`
```
add <reg>, <reg>
add <reg>, <mem>
add <mem>, <reg>
add <reg>, <constant>
add <mem>, <constant>
```
- Adds (or subtracts), storing result in first operand
- Similar restrictions as with data movement instructions:
- Destination cannot be a constant
- Memory cannot be accessed twice
</script></section>
<section data-markdown><script type="text/template">
## Arithmetic Instructions, part 2
- `inc`, `dec` (increment and decrement by one)
```
inc <reg>
inc <mem>
```
- Specific examples:
```
dec eax
inc [var]
```
- `imul`
```
imul <reg32>, <reg32> (or <mem>)
imul <reg32>, <reg32> (or <mem>), <con>
```
- `idiv`
- Divide 64-bit integer in EDX:EAX by operand
```
idiv ebx
```
</script></section>
<section data-markdown><script type="text/template">
## Logical Instructions
- `and`, `or`, `xor`
```
and <reg>, <reg>
and <reg>, <mem>
and <mem>, <reg>
```
- Specific examples:
```
and eax, 0fH
xor ecx, ecx
```
</script></section>
<section data-markdown><script type="text/template">
## Control Instructions, part 1
- `jmp <label>`
- go to instruction address specified by label
- `cmp`
- This must be done prior to an *conditional* jump
- cmp operand1, operand2
- Operand1 can be a register or memory (variable)
- Operand2 can be a register, memory (variable), or a constant
- Recall that you can't access memory twice!
- Sets the *machine status word*
</script></section>
<section data-markdown><script type="text/template">
## Control Instructions, part 2
- Conditional jumps: j*condition*
- Uses the machine status word, which was set via `cmp`
- Which holds info about the results of the last instruction
- There are many 'condition's to determine whether to jump
- Example: `je <label>`
- Jump when condition code equal is set
- Others: `jne`, `jz`, `jg`, `jge`, `jl`, `jle`, `js`, etc.
</script></section>
<section data-markdown><script type="text/template">
## Control Instructions, part 3
- `call <label>`
- Subroutine call
- Pushes address of the *next* instruction onto the stack, then unconditionally jumps to the label
- `ret`
- Subroutine return
- Pops the return address from the stack, then jumps to that address
</script></section>
<section>
<h2>A code block in both C/C++ and Assembly</h2>
<table class="transparent">
<tr><td><p>C/C++ code:</p><pre><code>int n = 5;
int i = 1;
int sum = 0;
while (i <= n) {
sum += i;
i++;
}</code></pre></td>
<td style="width:50px"></td>
<td><p>Assembly code:</p><pre><code>section .data
n DD 5
i DD 1
sum DD 0
section .text
loop: mov ecx, [i]
cmp ecx, [n]
jg endOfLoop
add [sum], ecx
inc [i]
jmp loop
endOfLoop:
</code></pre></td></tr></table>
</section>
</section>
<section>
<section id="callingconv" data-markdown><script type="text/template">
# Calling Conventions
</script></section>
<section data-markdown><script type="text/template">
## Calling of a subroutine
```
int max(int x, int y) {
int theMax = (x > y) ? x : y;
return theMax;
}
int main() {
int a = 5, b = 6;
int maxVal = max(a,b);
cout << "Max value: " << maxVal << endl;
return 0;
}
```
</script></section>
<section data-markdown><script type="text/template">
## Calling Conventions
- What is a calling convention?
- A set of rules/expectations between functions
- How (and where) are *parameters* passed?
- Which *registers* does the calling function expect to be preserved?
- Where should *local variables* be stored?
- How/where should results be *returned* from functions?
- Why?
- Separate programmers can:
- Share code more easily
- Develop libraries
</script></section>
<section data-markdown><script type="text/template">
## C Calling Convention
- Why C's calling convention?
- It's important
- Is used with both C and C++ code
- Can enable calling C library functions from assembly code
- Or other languages, too
</script></section>
<section data-markdown><script type="text/template">
## C Calling Convention
- Uses hardware stack (memory)
- Stack *grows down*, toward the lower memory addresses
- x86 instructions used for calling convention
- `pop`
- `push`
- `call`
- `ret`
- Using a stack for calling convention is implemented on most processors. Why?
- Recursion
</script></section>
<section data-markdown><script type="text/template">
## C Calling Convention Overview
- Answers to questions
- Parameters: passed on the stack
- Registers: saved on the stack
- Local variables: placed in memory on the stack
- Return value: eax register
</script></section>
<section data-markdown><script type="text/template">
## Calling Convention Overview
- Two sets of rules
- Caller: the function which calls another function
- Callee: the function which is called by another function
</script></section>
<section data-markdown><script type="text/template">
## Caller vs. Callee
```
void foo() {
// some function code ...
}
int main() {
foo();
return 0;
}
```
- `main()` is the *caller*
- `foo()` is the *callee*
</script></section>
<section data-markdown><script type="text/template">
## Register usage
- One register is used for the return value: eax
- Three registers may be modified by the callee: eax, ecx, edx
- If the caller wants to keep those values, they need to be saved by pushing them onto the stack
- And note eax is where the return value goes
- Three registers may not be modified by a subroutine call: ebx, edi, esi
- If the subroutine wants to modify them, it needs to back them up first (onto the stack) and restore them before returning
- Two registers should almost never be modified directly: ebp, esp
- There is an exception: ebp is modified in one case by the callee
</script></section>
<section data-markdown><script type="text/template">
## Varying number of parameters
- Three ways to have a variable number of parameters:
- Method overloading
- `Foo::bar(int)` and `Foo::bar(int, float)`
- Default parameters
- `Foo::bar (int x = 3)`
- Variable arguments
- As seen next...
</script></section>
<section data-markdown><script type="text/template">
## Variable number of arguments in C/C++
This code adapted from [here](http://www.cprogramming.com/tutorial/lesson17.html)
```
#include <cstdarg>
#include <iostream>
using namespace std;
double average (int num, ...) {
va_list arguments;
double sum = 0;
va_start (arguments, num);
for ( int x = 0; x < num; x++ )
sum += va_arg (arguments, double);
va_end (arguments);
return sum / num;
}
int main() {
cout << average(3, 12.2, 22.3, 4.5) << endl;
cout << average(5, 3.3, 2.2, 1.1, 5.5, 3.3) << endl;
}
```
</script></section>
<section data-markdown><script type="text/template">
## Dissection of the average() function
- Create a data structure to hold the list of arguments:
```
va_list arguments;
```
- Initialize the arguments to store all values after num:
```
va_start ( arguments, num );
```
- Loop until all numbers are added:
```
for ( int x = 0; x < num; x++ )
```
- Adds the next value in argument list to sum:
```
sum += va_arg ( arguments, double );
```
- Clean up the list:
```
va_end ( arguments );
```
- Return the average:
```
return sum / num;
```
</script></section>
<section data-markdown><script type="text/template">
## Example: Output in C
The C equivalent of cout is a function called `printf`
```
printf ("A %s, a %s, a %s: %s!\n", "man",
"plan", "canal", "Panama");
printf ("A percent sign: %%\n");
printf ("An int: %d\n", i);
printf ("A float with 2 decimal digits: %.2f\n",
float_value);
```
Output:
```
A man, a plan, a canal: Panama!
A percent sign: %
An int: 3
A float with 2 decimal digits: 3.14
```
</script></section>
</section>
<section>
<section id="caller" data-markdown><script type="text/template">
# Caller Rules
</script></section>
<section data-markdown><script type="text/template">
## Caller Summary
- Prologue
- Tasks to take care of BEFORE calling a subroutine
- Call the subroutine with the `call` opcode
- Epilogue
- Tasks to complete AFTER subroutine call returns
- (It is not really called this, but I use this to parallel the equivalent components in the callee convention)
</script></section>
<section data-markdown><script type="text/template">
## Callee Summary
- Prologue
- Tasks to perform BEFORE executing the function body
- Function body
- Epilogue
- Tasks to perform AFTER executing function body, but BEFORE leaving function
</script></section>
<section data-markdown><script type="text/template">
## Caller Rules/Responsibilities
- *Before* calling the function (the prologue)
- Save registers that might be needed after the call (eax, ecx, edx)
- Push parameters on the stack
- *Call* the function
- `call` instruction places return address in stack
- *After* the called function returns (the epilogue)
- Remove parameters from stack
- Restore saved registers
</script></section>
<section data-markdown><script type="text/template">
## Caller Rules ("Prologue")
1. Caller-saved registers
- Registers which the calling function (caller) must save (push onto the stack) ONLY if it wants the values preserved.
- eax, ecx, edx
2. Parameters
- Pushed in *reverse order* (last parameter first) onto stack
3. Call the subroutine
- Use the `call` instruction
- pushes the return address onto the stack and branches to the subroutine
</script></section>
<section data-markdown><script type="text/template">
## Caller Rules ("Epilogue")
1. Remove parameters
- Parameters pushed onto stack must be removed
- Restore stack to the state before the call
- What is done with the parameters?
2. Return value
- If any, held in eax
3. Restore caller-saved registers
- eax, ecx, edx
- `pop` them off the stack (Caller can assume no other registers were modified)
</script></section>
<section data-markdown><script type="text/template">
## Caller Rules Example
We'll see this code in the following slides:
```
int myFunc(int a, int b, int c) {
int result;
// some code
return result;
}
int main() {
int x = 1, z = 3;
int retVal = myFunc(x, 123, z);
//...
return 0;
}
```
</script></section>
<section data-markdown><script type="text/template">
## Caller Rules Example
```
push edx ; caller wants edx to be preserved
; int retVal = myFunc(x, 123, z);
push [z] ; Push last param first
push 123 ; push constant 123
push eax ; push first param last
call myFunc ; call the function
add esp, 12 ; clean up stack
pop edx ; restore saved edx value
; return value of myFunc is now available in eax
; (if there is any return value)
```
</script></section>
<section>
<h2>Stack Memory Visualization for myFunc</h2>
<p>This is just before the <code>call</code> opcode is invoked.</p>
<hr>
<table class="transparent">
<tr><td>↑</td><td style="width:50px"></td><td class="border" style="width:300px">value of edx</td><td style="width:25px"></td><td> </td></tr>
<tr><td>To higher addresses</td><td style="width:50px"></td><td class="border" style="width:300px">copy of var z</td><td style="width:25px"></td><td> </td></tr>
<tr><td>(to 0xffffffff)</td><td style="width:50px"></td><td class="border" style="width:300px">123</td><td style="width:25px"></td><td> </td></tr>
<tr><td></td><td style="width:50px"></td><td class="border" style="width:300px">value of eax (var x)</td><td style="width:25px"></td><td>← esp</td></tr>
<tr><td></td><td style="width:50px"></td><td class="border" style="width:300px"> </td><td style="width:25px"></td><td> </td></tr>
<tr><td></td><td style="width:50px"></td><td class="border" style="width:300px"> </td><td style="width:25px"></td><td> </td></tr>
<tr><td>To lower addresses</td><td style="width:50px"></td><td class="border" style="width:300px"> </td><td style="width:25px"></td><td> </td></tr>
<tr><td>(to 0x00000000)</td><td style="width:50px"></td><td class="border" style="width:300px"> </td><td style="width:25px"></td><td> </td></tr>
<tr><td>↓</td><td style="width:50px"></td><td class="border" style="width:300px;border-bottom:medium solid;"> </td><td style="width:25px"></td><td> </td></tr>
</table>
</section>
<section data-transition="fade" data-transition-speed="fast">
<h2>Stack Memory Visualization for myFunc</h2>
<p>This is just <i><b>after</b></i> the <code>call</code> opcode is invoked.</p>
<hr>
<table class="transparent">
<tr><td>↑</td><td style="width:50px"></td><td class="border" style="width:300px">value of edx</td><td style="width:25px"></td><td> </td></tr>
<tr><td>To higher addresses</td><td style="width:50px"></td><td class="border" style="width:300px">copy of var z</td><td style="width:25px"></td><td> </td></tr>
<tr><td>(to 0xffffffff)</td><td style="width:50px"></td><td class="border" style="width:300px">123</td><td style="width:25px"></td><td> </td></tr>
<tr><td></td><td style="width:50px"></td><td class="border" style="width:300px">value of eax (var x)</td><td style="width:25px"></td><td> </td></tr>
<tr><td></td><td style="width:50px"></td><td class="border" style="width:300px">return address</td><td style="width:25px"></td><td>← esp</td></tr>
<tr><td></td><td style="width:50px"></td><td class="border" style="width:300px"> </td><td style="width:25px"></td><td> </td></tr>
<tr><td>To lower addresses</td><td style="width:50px"></td><td class="border" style="width:300px"> </td><td style="width:25px"></td><td> </td></tr>
<tr><td>(to 0x00000000)</td><td style="width:50px"></td><td class="border" style="width:300px"> </td><td style="width:25px"></td><td> </td></tr>
<tr><td>↓</td><td style="width:50px"></td><td class="border" style="width:300px;border-bottom:medium solid;"> </td><td style="width:25px"></td><td> </td></tr>
</table>
</section>
</section>
<section>
<section id="callee" data-markdown><script type="text/template">
# Callee Rules
</script></section>
<section data-markdown><script type="text/template">
## Callee Summary (again)
- Prologue
- Tasks to perform BEFORE executing the function body
- Function body
- Epilogue
- Tasks to perform AFTER executing function body, but BEFORE leaving function
</script></section>
<section data-markdown><script type="text/template">
## Caller Rules Example
We'll see this code in the following slides:
```
int myFunc(int a, int b, int c) {
int result;
// some code
return result;
}
int main() {
int x = 1, z = 3;
int retVal = myFunc(x, 123, z);
//...
return 0;
}
```
</script></section>
<section data-markdown><script type="text/template">
## Callee Rules (Prologue)
Before the body of the function:
1. Push ebp and copy esp into ebp
```
push ebp
mov ebp, esp
```
- ebp: snapshot of esp when subroutine starts
- Parameters and local variables are known distances/offsets from this pointer value
2. Allocate local variables
- Make space on stack (decrement stack pointer)
```
sub esp, 4
```
</script></section>
<section>
<h2>Callee Rules (Prologue)</h2>
<ol start="3">
<li>Save callee-save registers<ul>
<li>ebx, edi, esi (push them onto stack)</li>
<li>only need to do this if callee intends to use them, otherwise, no need to save their contents</li>
</ul></li></ol>
<p> </p>
<p>THEN, perform body of the function</p>
</section>
<section data-markdown><script type="text/template">
## Callee Rules (Epilogue)
1. Return value saved to eax
2. Restore callee-saved registers
- `pop` from stack (in reverse order from which pushed)
3. Deallocate local variables
```
mov esp, ebp
```
4. Restore base pointer
```
pop ebp
```
5. Return
```
ret
```
</script></section>
<section data-markdown><script type="text/template">
## Callee Rules Example
With a bit more code in the `myFunc()` body:
```
int myFunc(int a, int b, int c) {
int result;
result = c;
result += b;
return result;
}
int main() {
int x = 1, z = 3;
int retVal = myFunc(x, 123, z);
//...
return 0;
}
```
</script></section>
<section data-markdown><script type="text/template">
## Callee Rules Example (1)
```
section .text
myFunc:
; prologue
push ebp ; save old base pointer
mov ebp, esp ; set new base pointer
sub esp, 4 ; save room for 1 local var (result)
push ebx ; save callee-save registers
push esi ; both will be used by myFunc
```
</script></section>
<section data-markdown><script type="text/template">
## Callee Rules Example (2)
```
; subroutine body
mov eax, [ebp+8] ; param 1 to eax
mov esi, [ebp+12] ; param 2 to esi
mov ebx, [ebp+16] ; param 3 to ebx
mov [ebp-4], ebx ; put ebx into local var
add [ebp-4], esi ; add esi into local var
mov eax, [ebp-4] ; mov contents of local var to eax
; (return value/final result)
```
</script></section>
<section data-markdown><script type="text/template">
## Callee Rules Example (3)
```
; subroutine epilogue
pop esi ; recover callee save registers
pop ebx ; REVERSE of when pushed
mov esp, ebp ; deallocate local var(s)
pop ebp ; restore caller's base pointer
ret ; pop top value from stack, jump there
```
</script></section>
<section>
<h2>Stack Memory Visualization for myFunc</h2>
<p>This is just <i>after</i> the caller invokes the <code>call</code> opcode.</p>
<hr>
<table class="transparent">
<tr><td>↑</td><td style="width:50px"></td><td class="border" style="width:300px">value of edx</td><td style="width:25px"></td><td>↖ ebp</td></tr>
<tr><td>To higher addresses</td><td style="width:50px"></td><td class="border" style="width:300px">copy of var z</td><td style="width:25px"></td><td> </td></tr>
<tr><td>(to 0xffffffff)</td><td style="width:50px"></td><td class="border" style="width:300px">123</td><td style="width:25px"></td><td> </td></tr>
<tr><td></td><td style="width:50px"></td><td class="border" style="width:300px">value of eax (var x)</td><td style="width:25px"></td><td> </td></tr>
<tr><td></td><td style="width:50px"></td><td class="border" style="width:300px">return address</td><td style="width:25px"></td><td>← esp</td></tr>
<tr><td></td><td style="width:50px"></td><td class="border" style="width:300px"> </td><td style="width:25px"></td><td> </td></tr>
<tr><td>To lower addresses</td><td style="width:50px"></td><td class="border" style="width:300px"> </td><td style="width:25px"></td><td> </td></tr>
<tr><td>(to 0x00000000)</td><td style="width:50px"></td><td class="border" style="width:300px"> </td><td style="width:25px"></td><td> </td></tr>
<tr><td>↓</td><td style="width:50px"></td><td class="border" style="width:300px;border-bottom:medium solid;"> </td><td style="width:25px"></td><td> </td></tr>
</table>
</section>
<section data-transition="fade" data-transition-speed="fast">
<h2>Stack Memory Visualization for myFunc</h2>
<p>This is just after the callee invokes the <code>push ebp</code> opcode.</p>
<hr>
<table class="transparent">
<tr><td>↑</td><td style="width:50px"></td><td class="border" style="width:300px">value of edx</td><td style="width:25px"></td><td>↖ ebp</td></tr>
<tr><td>To higher addresses</td><td style="width:50px"></td><td class="border" style="width:300px">copy of var z</td><td style="width:25px"></td><td> </td></tr>
<tr><td>(to 0xffffffff)</td><td style="width:50px"></td><td class="border" style="width:300px">123</td><td style="width:25px"></td><td> </td></tr>
<tr><td></td><td style="width:50px"></td><td class="border" style="width:300px">value of eax (var x)</td><td style="width:25px"></td><td> </td></tr>
<tr><td></td><td style="width:50px"></td><td class="border" style="width:300px">return address</td><td style="width:25px"></td><td> </td></tr>
<tr><td></td><td style="width:50px"></td><td class="border" style="width:300px">ebp backup</td><td style="width:25px"></td><td>← esp</td></tr>
<tr><td>To lower addresses</td><td style="width:50px"></td><td class="border" style="width:300px"> </td><td style="width:25px"></td><td> </td></tr>
<tr><td>(to 0x00000000)</td><td style="width:50px"></td><td class="border" style="width:300px"> </td><td style="width:25px"></td><td> </td></tr>
<tr><td>↓</td><td style="width:50px"></td><td class="border" style="width:300px;border-bottom:medium solid;"> </td><td style="width:25px"></td><td> </td></tr>
</table>
</section>
<section data-transition="fade" data-transition-speed="fast">
<h2>Stack Memory Visualization for myFunc</h2>
<p>This is after the <code>myFunc()</code> prologue is completed.</p>
<hr>
<table class="transparent">
<tr><td>↑</td><td style="width:50px"></td><td class="border" style="width:300px">value of edx</td><td style="width:25px"></td><td> </td></tr>
<tr><td>To higher addresses</td><td style="width:50px"></td><td class="border" style="width:300px">copy of var z</td><td style="width:25px"></td><td>[ebp+16]</td></tr>
<tr><td>(to 0xffffffff)</td><td style="width:50px"></td><td class="border" style="width:300px">123</td><td style="width:25px"></td><td>[ebp+12]</td></tr>
<tr><td></td><td style="width:50px"></td><td class="border" style="width:300px">value of eax (var x)</td><td style="width:25px"></td><td>[ebp+8]</td></tr>
<tr><td></td><td style="width:50px"></td><td class="border" style="width:300px">return address</td><td style="width:25px"></td><td> </td></tr>
<tr><td></td><td style="width:50px"></td><td class="border" style="width:300px">ebp backup</td><td style="width:25px"></td><td>← ebp</td></tr>
<tr><td>To lower addresses</td><td style="width:50px"></td><td class="border" style="width:300px">local variable</td><td style="width:25px"></td><td>[ebp-4]</td></tr>
<tr><td>(to 0x00000000)</td><td style="width:50px"></td><td class="border" style="width:300px">saved value of ebx</td><td style="width:25px"></td><td> </td></tr>
<tr><td>↓</td><td style="width:50px"></td><td class="border" style="width:300px;border-bottom:medium solid;">saved value of esi</td><td style="width:25px"></td><td>← esp</td></tr>
</table>
</section>
<section>
<table class="transparent">
<tr>
<td>
<!-- code block table -->
<small>
<table class="transparent">
<tr><td><span style="font-size:larger">Code</span></td></tr>
<tr><td style="vertical-align:top">
<table class="transparent" style="padding:0;spacing:0;border-spacing:0;border-collapse:collapse">
<tr><td><pre style="margin-top:0px;margin-bottom:0px"><code>push ebp</code></pre></td> <td><span class="fragment" data-fragment-index="1"><span class="fragment fade-out" data-fragment-index="3"><span style="font-size:larger">←</span></span></span></td></tr>
<tr><td><pre style="margin-top:0px;margin-bottom:0px"><code>mov ebp, esp</code></pre></td> <td><span class="fragment" data-fragment-index="3"><span class="fragment fade-out" data-fragment-index="6"><span style="font-size:larger">←</span></span></span></td></tr>
<tr><td><pre style="margin-top:0px;margin-bottom:0px"><code>sub esp, 4</code></pre></td> <td><span class="fragment" data-fragment-index="6"><span class="fragment fade-out" data-fragment-index="8"><span style="font-size:larger">←</span></span></span></td></tr>
<tr><td><pre style="margin-top:0px;margin-bottom:0px"><code>push ebx</code></pre></td> <td><span class="fragment" data-fragment-index="8"><span class="fragment fade-out" data-fragment-index="10"><span style="font-size:larger">←</span></span></span></td></tr>
<tr><td><pre style="margin-top:0px;margin-bottom:0px"><code>push esi</code></pre></td> <td><span class="fragment" data-fragment-index="10"><span class="fragment fade-out" data-fragment-index="12"><span style="font-size:larger">←</span></span></span></td></tr>
<tr><td><pre style="margin-top:0px;margin-bottom:0px"><code>mov eax, [ebp+8]</code></pre></td> <td><span class="fragment" data-fragment-index="12"><span class="fragment fade-out" data-fragment-index="14"><span style="font-size:larger">←</span></span></span></td></tr>
<tr><td><pre style="margin-top:0px;margin-bottom:0px"><code>mov esi, [ebp+12]</code></pre></td><td><span class="fragment" data-fragment-index="14"><span class="fragment fade-out" data-fragment-index="16"><span style="font-size:larger">←</span></span></span></td></tr>
<tr><td><pre style="margin-top:0px;margin-bottom:0px"><code>mov ebx, [ebp+16]</code></pre></td><td><span class="fragment" data-fragment-index="16"><span class="fragment fade-out" data-fragment-index="18"><span style="font-size:larger">←</span></span></span></td></tr>
<tr><td><pre style="margin-top:0px;margin-bottom:0px"><code>mov [ebp-4], ebx</code></pre></td> <td><span class="fragment" data-fragment-index="18"><span class="fragment fade-out" data-fragment-index="20"><span style="font-size:larger">←</span></span></span></td></tr>
<tr><td><pre style="margin-top:0px;margin-bottom:0px"><code>add [ebp-4], esi</code></pre></td> <td><span class="fragment" data-fragment-index="20"><span class="fragment fade-out" data-fragment-index="22"><span style="font-size:larger">←</span></span></span></td></tr>
<tr><td><pre style="margin-top:0px;margin-bottom:0px"><code>mov eax, [ebp-4]</code></pre></td> <td><span class="fragment" data-fragment-index="22"><span class="fragment fade-out" data-fragment-index="24"><span style="font-size:larger">←</span></span></span></td></tr>
<tr><td><pre style="margin-top:0px;margin-bottom:0px"><code>pop esi</code></pre></td> <td><span class="fragment" data-fragment-index="24"><span class="fragment fade-out" data-fragment-index="26"><span style="font-size:larger">←</span></span></span></td></tr>
<tr><td><pre style="margin-top:0px;margin-bottom:0px"><code>pop ebx</code></pre></td> <td><span class="fragment" data-fragment-index="26"><span class="fragment fade-out" data-fragment-index="28"><span style="font-size:larger">←</span></span></span></td></tr>
<tr><td><pre style="margin-top:0px;margin-bottom:0px"><code>mov esp, ebp</code></pre></td> <td><span class="fragment" data-fragment-index="28"><span class="fragment fade-out" data-fragment-index="30"><span style="font-size:larger">←</span></span></span></td></tr>