Convert C/C++ code to assembly language

The C/C++ compiler turn the given C/C++ source code into the Assembly Code. Then it is converted to the object code. We can use this property to convert the C or C++ code to assembly code.

We use gcc compiler to turn provided C/C++ code into assembly language. To see the assembly code generated by the C/C++ compiler, we can use the "-S" option on the command line:

Syntax for C

gcc -S filename.c

Syntax for C++

g++ -S filename.cpp

This will cause gcc to run the compiler, generating an assembly file.

Example

Suppose we write a C code and store it in a file name "source.c" or "source.cpp".

// C++ code stored in source2.cpp file
#include <iostream>

// Driver Code
int main()
{
    // Declaring variables
    int a = 2000, b =17;
    
    // Printing statement
    cout << a << " + " << b << ": " << a + b;
    
    return 0;
}

// C code stored in geeks.c file
#include <stdio.h>

// global string
char s[] = "GeeksforGeeks";

// Driver Code
int main()
{
	// Declaring variables
	int a = 2000, b =17;
	
	// Printing statement
	printf("%s %d \n", s, a+b);
}

Running the command: gcc -S geeks.c

This will cause gcc to run the compiler, generating an assembly file source.s, and go no further. (Normally it would then invoke the assembler to generate an object- code file.)

The assembly-code file contains various declarations including the set of lines: 

	.file	"source.c"
	.text
	.def	printf;	.scl	3;	.type	32;	.endef
	.seh_proc	printf
printf:
	pushq	%rbp
	.seh_pushreg	%rbp
	pushq	%rbx
	.seh_pushreg	%rbx
	subq	$56, %rsp
	.seh_stackalloc	56
	leaq	48(%rsp), %rbp
	.seh_setframe	%rbp, 48
	.seh_endprologue
	movq	%rcx, 32(%rbp)
	movq	%rdx, 40(%rbp)
	movq	%r8, 48(%rbp)
	movq	%r9, 56(%rbp)
	leaq	40(%rbp), %rax
	movq	%rax, -16(%rbp)
	movq	-16(%rbp), %rbx
	movl	$1, %ecx
	movq	__imp___acrt_iob_func(%rip), %rax
	call	*%rax
	movq	%rbx, %r8
	movq	32(%rbp), %rdx
	movq	%rax, %rcx
	call	__mingw_vfprintf
	movl	%eax, -4(%rbp)
	movl	-4(%rbp), %eax
	addq	$56, %rsp
	popq	%rbx
	popq	%rbp
	ret
	.seh_endproc
	.globl	s
	.data
	.align 8
s:
	.ascii "GeeksforGeeks\0"
	.def	__main;	.scl	2;	.type	32;	.endef
	.section .rdata,"dr"
.LC0:
	.ascii "%s %d \12\0"
	.text
	.globl	main
	.def	main;	.scl	2;	.type	32;	.endef
	.seh_proc	main
main:
	pushq	%rbp
	.seh_pushreg	%rbp
	movq	%rsp, %rbp
	.seh_setframe	%rbp, 0
	subq	$48, %rsp
	.seh_stackalloc	48
	.seh_endprologue
	call	__main
	movl	$2000, -4(%rbp)
	movl	$17, -8(%rbp)
	movl	-4(%rbp), %edx
	movl	-8(%rbp), %eax
	addl	%edx, %eax
	movl	%eax, %r8d
	leaq	s(%rip), %rdx
	leaq	.LC0(%rip), %rcx
	call	printf
	movl	$0, %eax
	addq	$48, %rsp
	popq	%rbp
	ret
	.seh_endproc
	.ident	"GCC: (tdm64-1) 10.3.0"
	.def	__mingw_vfprintf;	.scl	2;	.type	32;	.endef

Each indented line in the above code corresponds to a single machine instruction.For example, the pushq instruction indicates that the contents of register %rbp should be pushed onto the program stack. All information about local variable names or data types has been stripped away. We still see a reference to the global variable s[]= "GeeksforGeeks", since the compiler has not yet determined where in memory this variable will be stored.

Same thing we can do with C++. We just have to use the g++ compiler.