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PORetrieving vptr(pointer to virtual Table aka VTABLE)from the Objdump utility?
 

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  1. PORetrieving vptr(pointer to virtual Table aka VTABLE)from the Objdump utility?
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    <p>How can we know the address of the <strong>VTABLEs</strong> (i.e corresponding vptr) using the objdump utility and dissembled code. vptr is generally stored in the first byte of object .(correct/edit this). There is this simple code using the virtual function : </p> <pre><code>class base { public: int x; virtual void func() { //test function } }; class der : public base { void func() { //test function } }; /* * */ int main() { int s = 9; base b; der d ; std::cout&lt;&lt;"the address of Vptr is = "&lt;&lt;(&amp;b+0)&lt;&lt;std::endl; std::cout&lt;&lt;"the value at Vptr is = "&lt;&lt;(int*)*(int*)((&amp;b+0))&lt;&lt;std::endl; return 0; } </code></pre> <p>following is the output of the code : </p> <pre><code>the address of Vptr is = 0x7fff86a78fe0 the value at Vptr is = **0x400c30** </code></pre> <p>Following is the part of main function - <strong>diassembly</strong> of the code : </p> <pre><code>base b; 4009b4: 48 8d 45 d0 lea -0x30(%rbp),%rax 4009b8: 48 89 c7 mov %rax,%rdi 4009bb: e8 f4 00 00 00 callq 400ab4 &lt;_ZN4baseC1Ev&gt; der d ; 4009c0: 48 8d 45 c0 lea -0x40(%rbp),%rax 4009c4: 48 89 c7 mov %rax,%rdi 4009c7: e8 fe 00 00 00 callq 400aca &lt;_ZN3derC1Ev&gt; </code></pre> <p>It shows here that _ZN4baseC1Ev is the address of the base object and _ZN3derC1Ev is the address of the derived object.</p> <p>in the _ZN4baseC1Ev</p> <pre><code>0000000000400ab4 &lt;_ZN4baseC1Ev&gt;: 400ab4: 55 push %rbp 400ab5: 48 89 e5 mov %rsp,%rbp 400ab8: 48 89 7d f8 mov %rdi,-0x8(%rbp) 400abc: 48 8b 45 f8 mov -0x8(%rbp),%rax 400ac0: 48 c7 00 30 0c 40 00 movq $0x400c30,(%rax) 400ac7: c9 leaveq 400ac8: c3 retq 400ac9: 90 nop 0000000000400aca &lt;_ZN3derC1Ev&gt;: } #include&lt;iostream&gt; class base { public: int x; virtual void func() 400a8a: 55 push %rbp 400a8b: 48 89 e5 mov %rsp,%rbp 400a8e: 48 89 7d f8 mov %rdi,-0x8(%rbp) { //test function } 400a92: c9 leaveq 400a93: c3 retq 0000000000400a94 &lt;_ZN3der4funcEv&gt;: }; class der : public base { void func() 400a94: 55 push %rbp 400a95: 48 89 e5 mov %rsp,%rbp 400a98: 48 89 7d f8 mov %rdi,-0x8(%rbp) { //test function } 400a9c: c9 leaveq 400a9d: c3 retq 0000000000400a9e &lt;_ZN4baseC2Ev&gt;: */ #include &lt;stdlib.h&gt; #include&lt;iostream&gt; class base { 400a9e: 55 push %rbp 400a9f: 48 89 e5 mov %rsp,%rbp 400aa2: 48 89 7d f8 mov %rdi,-0x8(%rbp) 400aa6: 48 8b 45 f8 mov -0x8(%rbp),%rax 400aaa: 48 c7 00 50 0c 40 00 movq $0x400c50,(%rax) 400ab1: c9 leaveq 400ab2: c3 retq 400ab3: 90 nop 0000000000400ab4 &lt;_ZN4baseC1Ev&gt;: 400ab4: 55 push %rbp 400ab5: 48 89 e5 mov %rsp,%rbp 400ab8: 48 89 7d f8 mov %rdi,-0x8(%rbp) 400abc: 48 8b 45 f8 mov -0x8(%rbp),%rax 400ac0: 48 c7 00 50 0c 40 00 movq $0x400c50,(%rax) 400ac7: c9 leaveq 400ac8: c3 retq 400ac9: 90 nop 0000000000400aca &lt;_ZN3derC1Ev&gt;: } }; </code></pre> <p>Here is the link to output of <a href="http://www.pastedump.com/paste/2220" rel="nofollow">objdump</a> -S exe file </p> <p><strong>also objdump -t virtualfunctionsize | grep vtable gives this :</strong> </p> <pre><code>0000000000400c40 w O .rodata 0000000000000018 vtable for base 0000000000601e00 g O .dtors 0000000000000000 .hidden __DTOR_END__ 0000000000400b00 g F .text 0000000000000089 __libc_csu_init 0000000000400c20 w O .rodata 0000000000000018 vtable for der </code></pre> <p>I wanted to know - what it is the <strong>VTABLE</strong> address and corresponding virtual function's denoted by it.</p> <ul> <li><p>the address of Vptr is = 0x7fff86a78fe0 , what does this represent - VTABLE location?</p></li> <li><p>the value at Vptr is = <strong>0x400c30</strong> - What does this represent - the first Virtual function of the base class?</p></li> <li><p>How can the subsequent addresses of the virtual functions of the derived classes can be found?</p></li> </ul> <p>Rgds, softy</p>
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    1. COHave you considered looking for the symbols with vtable in their name?
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      1. PORetrieving vptr(pointer to virtual Table aka VTABLE)from the Objdump utility?
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    2. COyes I did, which specific function you want me to look into.?
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    3. CO@soty: not function, the symbols with vtable in their name are the vtables
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