Exercise 3: Constructing C Code From x86 Assembly

by | May 31, 2022 | Exclusive Articles, Featured, Reverse Engineering

Exercise - 3 Constructing C Code From x86 Assembly

In this article, we will look into the x86 assembly code, analyze it and try to construct the corresponding C code. Let’s look into the following x64 assembly code:

0000000000400546 <main>:
  400546:	push   rbp
  400547:	mov    rbp,rsp
  40054a:	sub    rsp,0x30
  40054e:	mov    rax,QWORD PTR fs:0x28
  400555:	00 00 
  400557:	mov    QWORD PTR [rbp-0x8],rax
  40055b:	xor    eax,eax
  40055d:	mov    WORD PTR [rbp-0x20],0x6948
  400563:	mov    BYTE PTR [rbp-0x1e],0x0
  400567:	mov    WORD PTR [rbp-0x10],0x6948
  40056d:	mov    BYTE PTR [rbp-0xe],0x0
  400571:	mov    DWORD PTR [rbp-0x24],0xffffffff
  400578:	mov    DWORD PTR [rbp-0x28],0x0
  40057f:	jmp    4005ab <main+0x65>
  400581:	mov    eax,DWORD PTR [rbp-0x28]
  400584:	cdqe   
  400586:	movzx  edx,BYTE PTR [rbp+rax*1-0x20]
  40058b:	mov    eax,DWORD PTR [rbp-0x28]
  40058e:	cdqe   
  400590:	movzx  eax,BYTE PTR [rbp+rax*1-0x10]
  400595:	cmp    dl,al
  400597:	je     4005a7 <main+0x61>
  400599:	mov    DWORD PTR [rbp-0x24],0x0
  4005a0:	mov    eax,0x0
  4005a5:	jmp    4005d3 <main+0x8d>
  4005a7:	add    DWORD PTR [rbp-0x28],0x1
  4005ab:	mov    eax,DWORD PTR [rbp-0x28]
  4005ae:	cdqe   
  4005b0:	movzx  eax,BYTE PTR [rbp+rax*1-0x20]
  4005b5:	test   al,al
  4005b7:	je     4005c7 <main+0x81>
  4005b9:	mov    eax,DWORD PTR [rbp-0x28]
  4005bc:	cdqe   
  4005be:	movzx  eax,BYTE PTR [rbp+rax*1-0x10]
  4005c3:	test   al,al
  4005c5:	jne    400581 <main+0x3b>
  4005c7:	mov    DWORD PTR [rbp-0x24],0x1
  4005ce:	mov    eax,0x0
  4005d3:	mov    rcx,QWORD PTR [rbp-0x8]
  4005d7:	xor    rcx,QWORD PTR fs:0x28
  4005de:	00 00 
  4005e0:	je     4005e7 <main+0xa1>
  4005e2:	call   400420 <__stack_chk_fail@plt>
  4005e7:	leave  
  4005e8:	ret    
  4005e9:	nop    DWORD PTR [rax+0x0]

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Amrita Mitra

Author

Ms. Amrita Mitra is an author, who has authored the books “Cryptography And Public Key Infrastructure“, “Web Application Vulnerabilities And Prevention“, “A Guide To Cyber Security” and “Phishing: Detection, Analysis And Prevention“. She is also the founder of Asigosec Technologies, the company that owns The Security Buddy.

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