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<title> | tait.tech</title>
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<h1 id="cmpt-295-unit---machine-level-programming">CMPT 295: Unit - Machine-Level Programming</h1>
<p>Lecture 18:</p>
<ul>
<li>Assembly language</li>
<li>Program Control</li>
<li>Function Call and Stack</li>
<li>Passing Data</li>
</ul>
<h2 id="last-lecture">Last Lecture</h2>
<ul>
<li>Function call mechanisms: 1) passing control, 2) passing data, 3)
managing local data on memory (stack)</li>
<li>Memory layout
<ul>
<li>Stack (local variables …)</li>
<li>Heap (dynamically allocated data)</li>
<li>Data (statically allocated data)</li>
<li>Text / Shared Libraries (program code)</li>
</ul>
</li>
<li>A “stack” is the right data structure for function call / return
<ul>
<li>If multstore calls mult2, then mult2 returns before multstore returns</li>
</ul>
</li>
<li>x86-64 stack register and instructions: stack pointer %rsp, push and pop</li>
<li>x86-64 function call instructions: call and ret</li>
</ul>
<h2 id="from-lecture-17--slide-14">From Lecture 17 – Slide 14</h2>
<p>Why 8?</p>
<ul>
<li>pushq src
<ul>
<li>Fetch value of operand src</li>
<li>Decrement %rsp by 8</li>
<li>Write value at address given by %rsp</li>
</ul>
</li>
<li>popq dest
<ul>
<li>Read value at %rsp (address) and
store it in operand dest (must be register)</li>
<li>Increment %rsp by 8</li>
</ul>
</li>
</ul>
<p>1) %rsp contains the memory address 0x0018</p>
<table>
<thead>
<tr>
<th>Register</th>
<th>Memory Address</th>
</tr>
</thead>
<tbody>
<tr>
<td>%rsp</td>
<td>0x0018</td>
</tr>
<tr>
<td> </td>
<td>0x0010</td>
</tr>
<tr>
<td> </td>
<td>0x0008</td>
</tr>
</tbody>
</table>
<p>2) %rsp contains the memory address 0x0010</p>
<table>
<thead>
<tr>
<th>Register</th>
<th>Memory Address</th>
</tr>
</thead>
<tbody>
<tr>
<td> </td>
<td>0x0018</td>
</tr>
<tr>
<td>%rsp</td>
<td>0x0010</td>
</tr>
<tr>
<td> </td>
<td>0x0008</td>
</tr>
</tbody>
</table>
<h2 id="todays-menu">Today’s Menu</h2>
<ul>
<li>Introduction
<ul>
<li>C program -&gt; assembly code -&gt; machine level code</li>
</ul>
</li>
<li>Assembly language basics: data, move operation
<ul>
<li>Memory addressing modes</li>
</ul>
</li>
<li>Operation leaq and Arithmetic &amp; logical operations</li>
<li>Conditional Statement – Condition Code + cmovX</li>
<li>Loops</li>
<li>(highlighted) Function call – Stack
<ul>
<li>Overview of Function Call</li>
<li>Memory Layout and Stack - x86-64 instructions and registers</li>
<li>Passing control</li>
<li>(highlighted) Passing data – Calling Conventions</li>
<li>Managing local data</li>
<li>Recursion</li>
</ul>
</li>
<li>Array</li>
<li>Buffer Overflow</li>
<li>Floating-point operations</li>
</ul>
<h2 id="2-passing-data-mechanism--using-stack-x86-64-function-call-convention">2. Passing data mechanism – using stack x86-64 function call convention</h2>
<ol>
<li>Caller and callee functions must obey function call convention when
passing data during function call
<ul>
<li>Caller:</li>
</ul>
<ul>
<li>Before calling the callee function, the caller must copy the callee’s arguments (1 to 6) into specific registers: If there is a …
<ul>
<li>1st argument -&gt; %rdi (or %edi, or %di or %dil)</li>
<li>2nd argument -&gt; %rsi (or %esi, or %si or %sil)</li>
<li>3rd argument -&gt; %rdx (or %edx, or %dx or %dl)</li>
<li>4th argument -&gt; %rcx (or %ecx, or %cx or %cl)</li>
<li>5th argument -&gt; %r8 (or %r8d, or %r8w or %r8b)</li>
<li>6th argument -&gt; %r9 (or %r9d, or %r9w or %r9b)
* Callee:</li>
</ul>
</li>
<li>Before returning to caller, callee must copy returned value into register %rax</li>
</ul>
</li>
</ol>
<h2 id="passing-data-mechanism--example-of-passing-arguments-in-registers-and-returning-return-value">Passing data mechanism – Example of passing arguments in registers and returning return value</h2>
<p>C code:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>long plus(long x, long y){
return x+y;
}
void sum_store(long x, long y, long *dest)
{
long sum = plus(x,y);
*dest = sum;
}
int main(int argc, char *argv[]) {
if (argc == 3) {
long x = atoi(argv[1]);
long y = atoi(argv[2]);
long result;
sum_store(x, y, &amp;result);
printf("%ld + %ld --&gt; %ld\n", x, y, result);
else printf("2 numbers required\n");
return 0;
}
</code></pre></div></div>
<p>Assembly code:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>sum_store:
.LFB40:
.cfi_startproc
endbr64
addq %rsi,%rdi
movq %rdi,(%rdx)
ret
main:
pushq %r13
pushq %r12
pushq %rbx
subq $16,%rsp
movq %fs:40,%rax
movq %rax,8(%rsp)
xorl %eax,%eax
cmpl $3,%edi # highlighted
je .L7 # highlighted
leaq .LC1(%rip), %rdi
call puts@PLT
.L3:
movq 8(%rsp),%rax
xorq %fs:40,%rax
jne .L8
addq $16,%rsp
xorl %eax,%eax
popq %rbx
popq %r12
popq %r13
ret
.L7:
movq 8(%rsi),%rdi
movq %rsi,%rbx
movl $10,%edx
xorl %esi,%esi
call strtol@PLT
movq 16(%rbx),%rdi
xorl %esi,%esi
movl $10,%edx
movslq %eax,%r12 # highlighted
call strtol@PLT
movq %rsp,%rdx # highlighted
movq %r12,%rdi # highlighted
movslq %eax,%r13 # highlighted
movq %r13,%rsi # highlighted
call sum_store@PLT # highlighted
movq (%rsp),%r8
movq %r13,%rcx
movq %r12,%rdx
leaq .LC0(%rip),%rsi
movl $1,%edi
xorl %eax,%eax
call __printf_chk@PLT
jmp .L3
.L8:
call __stack_chk_fail@PLT
</code></pre></div></div>
<h2 id="what-if-the-callee-function-has-more-than-6-arguments">What if the callee function has more than 6 arguments?</h2>
<ol>
<li>Caller and callee functions must obey function call convention when passing data during function call
<ul>
<li>Caller:</li>
</ul>
<ul>
<li>Before calling the callee function, the caller must copy the callee’s arguments (1 to 6) into specific registers: …</li>
<li>If a callee function has more than 6 arguments … then must push the rest of the arguments on the stack in reverse order
* Callee:</li>
<li>Before returning to caller, callee must copy returned value into register %rax</li>
</ul>
</li>
</ol>
<h2 id="2-passing-data-mechanism--using-stack-x86-64-function-call-convention-1">2. Passing data mechanism – using stack x86-64 function call convention</h2>
<p>2) When passing data that is a memory address (i.e., a
pointer) during function call</p>
<ul>
<li>Caller:
<ul>
<li>Must make use of the stack in order to create such memory address</li>
</ul>
</li>
</ul>
<h2 id="passing-data-mechanism--examples-of-local-variables-arguments-and-pointers-on-the-stack">Passing data mechanism – Examples of local variables, arguments and pointers on the stack</h2>
<p>C code:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>long call_proc()
{
long x1 = 1; //How to push x4 and &amp;x4 onto stack?
int x2 = 2;
short x3 = 3;
char x4 = 4;
proc(x1, &amp;x1, x2, &amp;x2,
x3, &amp;x3, x4, &amp;x4);
return (x1+x2)*(x3-x4);
}
</code></pre></div></div>
<p>Assembly:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>call_proc:
subq $40, %rsp
movq $1, 32(%rsp) # local variable
movl $2, 28(%rsp) # local variable
movw $3, 26(%rsp) # local variable
movb $4, 25(%rsp) # local variable
movq 32(%rsp), %rdi
movl 28(%rsp), %edx
leaq 25(%rsp), %rax
movq %rax, 8(%rsp)
movl $4, (%rsp)
leaq 32(%rsp), %rsi
leaq 28(%rsp), %rcx
leaq 26(%rsp), %r9
movl $3, %r8d
callq proc
...
</code></pre></div></div>
<table>
<thead>
<tr>
<th>base + displacement</th>
<th>Stack Variable</th>
</tr>
</thead>
<tbody>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
</tbody>
</table>
<p>Register Table:</p>
<table>
<thead>
<tr>
<th>Register</th>
<th>Value</th>
</tr>
</thead>
<tbody>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
</tbody>
</table>
<h2 id="summary">Summary</h2>
<ul>
<li>Passing data mechanism
<ul>
<li>x86-64 function call convention:</li>
</ul>
</li>
</ul>
<p>First 6 arguments:</p>
<table>
<thead>
<tr>
<th>Name</th>
<th>Register</th>
</tr>
</thead>
<tbody>
<tr>
<td>argument 1</td>
<td>%rdi</td>
</tr>
<tr>
<td>argument 2</td>
<td>%rsi</td>
</tr>
<tr>
<td>argument 3</td>
<td>%rdx</td>
</tr>
<tr>
<td>argument 4</td>
<td>%rcx</td>
</tr>
<tr>
<td>argument 5</td>
<td>%r8</td>
</tr>
<tr>
<td>argument 6</td>
<td>%r9</td>
</tr>
<tr>
<td>return value</td>
<td>%rax</td>
</tr>
</tbody>
</table>
<p>Stack:</p>
<table>
<tbody>
<tr>
<td>Register</td>
<td>Stack</td>
<td>Note</td>
</tr>
<tr>
<td> </td>
<td>…</td>
<td> </td>
</tr>
<tr>
<td> </td>
<td>argument n</td>
<td>Stored onto the stack in reverse order</td>
</tr>
<tr>
<td> </td>
<td>…</td>
<td>Stored onto the stack in reverse order</td>
</tr>
<tr>
<td> </td>
<td>argument 8</td>
<td>Stored onto the stack in reverse order</td>
</tr>
<tr>
<td>%rsp</td>
<td>argument 7</td>
<td>Stored onto the stack in reverse order</td>
</tr>
</tbody>
</table>
<h2 id="next-lecture">Next Lecture</h2>
<ul>
<li>Introduction
<ul>
<li>C program -&gt; assembly code -&gt; machine level code</li>
</ul>
</li>
<li>Assembly language basics: data, move operation
<ul>
<li>Memory addressing modes</li>
</ul>
</li>
<li>Operation leaq and Arithmetic &amp; logical operations</li>
<li>Conditional Statement – Condition Code + cmovX</li>
<li>Loops</li>
<li>(highlighted) Function call – Stack
<ul>
<li>Overview of Function Call</li>
<li>Memory Layout and Stack - x86-64 instructions and registers</li>
<li>Passing control</li>
<li>Passing data – Calling Conventions</li>
<li>(highlighted) Managing local data</li>
<li>(highlighted) Recursion</li>
</ul>
</li>
<li>Array</li>
<li>Buffer Overflow</li>
<li>Floating-point operations</li>
</ul>
<footer>
</footer>
</div>
</main>
</body>
</html>