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PODissassembling a C function in GDB. Clarification on GAS Assembly instructions
 

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    <p>I have a C function written here ( It does have a buffer overflow vulnerability )</p> <pre><code>void func(char *str) { char buffer[12]; int a=9; strcpy(buffer,str); } </code></pre> <p>Its assembly in gdb translates to</p> <pre><code>|0x4005b4 &lt;func&gt; push %rbp |0x4005b5 &lt;func+1&gt; mov %rsp,%rbp |0x4005b8 &lt;func+4&gt; sub $0x40,%rsp |0x4005bc &lt;func+8&gt; mov %rdi,-0x38(%rbp) |0x4005c0 &lt;func+12&gt; mov %fs:0x28,%rax |0x4005c9 &lt;func+21&gt; mov %rax,-0x8(%rbp) |0x4005cd &lt;func+25&gt; xor %eax,%eax |0x4005cf &lt;func+27&gt; movl $0x9,-0x24(%rbp) |0x4005d6 &lt;func+34&gt; mov -0x38(%rbp),%rdx |0x4005da &lt;func+38&gt; lea -0x20(%rbp),%rax |0x4005de &lt;func+42&gt; mov %rdx,%rsi |0x4005e1 &lt;func+45&gt; mov %rax,%rdi |0x4005e4 &lt;func+48&gt; callq 0x400490 &lt;strcpy@plt&gt; |0x4005e9 &lt;func+53&gt; mov -0x8(%rbp),%rax |0x4005ed &lt;func+57&gt; xor %fs:0x28,%rax |0x4005f6 &lt;func+66&gt; je 0x4005fd &lt;func+73&gt; |0x4005f8 &lt;func+68&gt; callq 0x4004a0 &lt;__stack_chk_fail@plt&gt; |0x4005fd &lt;func+73&gt; leaveq |0x4005fe &lt;func+74&gt; retq </code></pre> <p><code>rdi</code> contains the address of the original character array passed to the function.</p> <p>1.In <code>func+8</code>, is moving this rdi value to -0x38(rbp) to save the value in local variable str of the function or does it have any other implications?</p> <p>2.What does the instruction at <code>func+8</code> accomplish? Is there anyway in gdb or in linux to view the contents of the <code>fs segment</code>?</p> <p>3.What do the instructions <code>func+12</code> to <code>func+25</code> do? </p> <p>EDIT: I compiled this in gcc 4.6.3 with -O0 </p>
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