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