In this article, we will learn how to construct C code from x86 assembly for structures. The article is divided into two parts. In the first part, we will write C code that involves structures and analyze the corresponding x86 assembly code. In the second part, we will look into x86 assembly code and try to construct corresponding C code that involves structures.

Let’s write this small piece of C code first.

#include <stdio.h>
struct s{
        int a;
        char b;
};
int main() {
        struct s ss;
        ss.a = 10;
        ss.b = 'a';
        return 0;
}

Now, we can compile the above C code using the GCC compiler and get the corresponding x86 assembly code using the following commands:

$ gcc structures.c
$ objdump -M intel -d a.out

Please note that the “-M intel” option will generate the x86 assembly code in the Intel syntax. The corresponding x86 assembly code will look like the following:

00000000004004d6 <main>:
  4004d6:	push   rbp
  4004d7:	mov    rbp,rsp
  4004da:	mov    DWORD PTR [rbp-0x10],0xa
  4004e1:	mov    BYTE PTR [rbp-0xc],0x61
  4004e5:	mov    eax,0x0
  4004ea:	pop    rbp
  4004eb:	ret    
  4004ec:	nop    DWORD PTR [rax+0x0]