How do you get assembler output from C/C++ source in gcc?

In this article, we will see how to generate the assembler output from C or C++ code using GCC.

What is GCC

The GCC, which stands for GNU Compiler Collection, is a set of compilers and development tools available for various operating systems such as Linux, Windows, and a wide variety of other OSs (operating systems).

It supports mostly C and C++, but also Objective-C, Ada, Go, Fortran, and D. The Free Software Foundation (FSF) created GCC and distributed it as totally free (as in libre) software.

How to Get Assembler Output

The GCC has a great feature that allows you to receive all intermediate outputs from a source code while it is being executed. To get the assembler output, use the gcc option >'-S'. This option displays the result after compilation but before passing it to the assembler.

Following is the syntax of this command:

gcc -S your_file.c
or
g++ -S your_file.cpp

The above command produces a file named your_file.s containing the assembly code.

To specify the output file name use the below command:

gcc -S -o output.s myfile.c

Get the Assembler Output

Here, in the following example, you create a program and run the above command to get the assembler output in C/C++:

#include <iostream>
using namespace std;
int main() {
   int x, y, sum;
   x = 50;
   y = 60;
   sum = x + y;
   cout << "Sum is: " << sum << endl;
}

Output

To get the assembler output of the above code, run the above command in the VS code or any other compiler.

	.file	"addition.cpp"
	.section .rdata,"dr"
__ZStL19piecewise_construct:
	.space 1
.lcomm __ZStL8__ioinit,1,1
	.def	___main;	.scl	2;	.type	32;	.endef
LC0:
	.ascii "Sum is: \0"
	.text
	.globl	_main
	.def	_main;	.scl	2;	.type	32;	.endef
_main:
LFB1445:
	.cfi_startproc
	leal	4(%esp), %ecx
	.cfi_def_cfa 1, 0
	andl	$-16, %esp
	pushl	-4(%ecx)
	pushl	%ebp
	.cfi_escape 0x10,0x5,0x2,0x75,0
	movl	%esp, %ebp
	pushl	%ecx
	.cfi_escape 0xf,0x3,0x75,0x7c,0x6
	subl	$36, %esp
	call	___main
	movl	$50, -12(%ebp)
	movl	$60, -16(%ebp)
	movl	-12(%ebp), %edx
	movl	-16(%ebp), %eax
	addl	%edx, %eax
	movl	%eax, -20(%ebp)
	movl	$LC0, 4(%esp)
	movl	$__ZSt4cout, (%esp)
	call	__ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc
	movl	%eax, %edx
	movl	-20(%ebp), %eax
	movl	%eax, (%esp)
	movl	%edx, %ecx
	call	__ZNSolsEi
	subl	$4, %esp
	movl	$__ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_, (%esp)
	movl	%eax, %ecx
	call	__ZNSolsEPFRSoS_E
	subl	$4, %esp
	movl	$0, %eax
	movl	-4(%ebp), %ecx
	.cfi_def_cfa 1, 0
	leave
	.cfi_restore 5
	leal	-4(%ecx), %esp
	.cfi_def_cfa 4, 4
	ret
	.cfi_endproc
LFE1445:
	.def	___tcf_0;	.scl	3;	.type	32;	.endef
___tcf_0:
LFB1878:
	.cfi_startproc
	pushl	%ebp
	.cfi_def_cfa_offset 8
	.cfi_offset 5, -8
	movl	%esp, %ebp
	.cfi_def_cfa_register 5
	subl	$8, %esp
	movl	$__ZStL8__ioinit, %ecx
	call	__ZNSt8ios_base4InitD1Ev
	leave
	.cfi_restore 5
	.cfi_def_cfa 4, 4
	ret
	.cfi_endproc
LFE1878:
	.def	__Z41__static_initialization_and_destruction_0ii;	.scl	3;	.type	32;	.endef
__Z41__static_initialization_and_destruction_0ii:
LFB1877:
	.cfi_startproc
	pushl	%ebp
	.cfi_def_cfa_offset 8
	.cfi_offset 5, -8
	movl	%esp, %ebp
	.cfi_def_cfa_register 5
	subl	$24, %esp
	cmpl	$1, 8(%ebp)
	jne	L6
	cmpl	$65535, 12(%ebp)
	jne	L6
	movl	$__ZStL8__ioinit, %ecx
	call	__ZNSt8ios_base4InitC1Ev
	movl	$___tcf_0, (%esp)
	call	_atexit
L6:
	nop
	leave
	.cfi_restore 5
	.cfi_def_cfa 4, 4
	ret
	.cfi_endproc
LFE1877:
	.def	__GLOBAL__sub_I_main;	.scl	3;	.type	32;	.endef
__GLOBAL__sub_I_main:
LFB1879:
	.cfi_startproc
	pushl	%ebp
	.cfi_def_cfa_offset 8
	.cfi_offset 5, -8
	movl	%esp, %ebp
	.cfi_def_cfa_register 5
	subl	$24, %esp
	movl	$65535, 4(%esp)
	movl	$1, (%esp)
	call	__Z41__static_initialization_and_destruction_0ii
	leave
	.cfi_restore 5
	.cfi_def_cfa 4, 4
	ret
	.cfi_endproc
LFE1879:
	.section	.ctors,"w"
	.align 4
	.long	__GLOBAL__sub_I_main
	.ident	"GCC: (MinGW.org GCC-6.3.0-1) 6.3.0"
	.def	__ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc;	.scl	2;	.type	32;	.endef
	.def	__ZNSolsEi;	.scl	2;	.type	32;	.endef
	.def	__ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_;	.scl	2;	.type	32;	.endef
	.def	__ZNSolsEPFRSoS_E;	.scl	2;	.type	32;	.endef
	.def	__ZNSt8ios_base4InitD1Ev;	.scl	2;	.type	32;	.endef
	.def	__ZNSt8ios_base4InitC1Ev;	.scl	2;	.type	32;	.endef
	.def	_atexit;	.scl	2;	.type	32;	.endef