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

Let’s first write a small piece of C code that uses conditional statements namely an if statement.

#include <stdio.h>
int main() {
        int a = 0;
        if(a == 0) {
                a = 1;
        }
	return 0;
}

Now, let’s compile the code and generate the object code using the GCC compiler. After that, we can use the objdump command to look into the corresponding assembly code.

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

Please note that the “-M intel” option will generate the assembly code in the Intel syntax.

The assembly code will look like the following:

0000000000000000 <main>:
   0:	push   rbp
   1:	mov    rbp,rsp
   4:	mov    DWORD PTR [rbp-0x4],0x0
   b:	cmp    DWORD PTR [rbp-0x4],0x0
   f:	jne    18 <main+0x18>
  11:	mov    DWORD PTR [rbp-0x4],0x1
  18:	mov    eax,0x0
  1d:	pop    rbp
  1e:	ret    

Now, let’s analyze the x86 assembly code. …