Stack Frames in x86 64-bit Processors or x64

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

We can save the above code in a file stack_frame.c and compile it using “gcc -c stack_frame.c”. This will create a file named stack_frame.o. After that, we can see the assembly code of the above C code using the following command:

$  gcc -c stack_frame.c
$ objdump -M intel -d stack_frame.o

Please note that we are using the Intel syntax and hence we are using the “-M intel” option with the objdump command. If we execute the above commands, the assembly code in the output will look like the following:

Disassembly of section .text:

0000000000000000 :
   push   rbp
   mov    rbp,rsp
   mov    DWORD PTR [rbp-0x14],edi
   mov    eax,DWORD PTR [rbp-0x14]
   add    eax,0x1
   mov    DWORD PTR [rbp-0x4],eax
   mov    eax,DWORD PTR [rbp-0x4]
   pop    rbp
   ret    

0000000000000015 <main>:
  push   rbp
  mov    rbp,rsp
  sub    rsp,0x10
  mov    DWORD PTR [rbp-0x8],0x1
  mov    eax,DWORD PTR [rbp-0x8]
  mov    edi,eax
  call   2e <main+0x19>
  mov    DWORD PTR [rbp-0x4],eax
  mov    eax,0x0
  leave  
  ret  

Firstly, let’s focus on the main function. The assembly code of the main function looks like the following:

0000000000000015 <main>:
  push   rbp
  mov    rbp,rsp
  sub    rsp,0x10
  mov    DWORD PTR [rbp-0x8],0x1
  mov    eax,DWORD PTR [rbp-0x8]
  mov    edi,eax
  call   2e <main+0x19>
  mov    DWORD PTR [rbp-0x4],eax
  mov    eax,0x0
  leave  
  ret   

As we discussed, when we call the main function, firstly the value of the RBP is pushed onto the stack and then the value of RSP is copied into RBP. The main function needs 16 bytes to store its data. So, 16 bytes are getting subtracted from the RSP register. This set of assembly instructions is executed in almost all function calls and it is called the function prologue.

Now, we are executing the function code of the main function. The main function looks like the following:

int main() {
        int a = 1, d;
        d = func(a);
        return 0;
}
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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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