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

Here we will see how to generate assembler output from C or C++ code using gcc.

The gcc provides a great feature to get all intermediate outputs from a source code while executing. To get the assembler output we can use the option ‘-S’ for the gcc. This option shows the output after compiling, but before sending to the assembler. The syntax of this command is like below.

gcc –S program.cpp

Now, let us see how to output will be look like. Here we are using a simple program. In this program two numbers are stored into the variables x and y, then store the sum into another variable, after that print the result.

Example

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

Output

   .file "test_cpp.cpp"
   .text
   .section .rodata
   .type _ZStL19piecewise_construct, @object
   .size _ZStL19piecewise_construct, 1
_ZStL19piecewise_construct:
   .zero 1
   .local _ZStL8__ioinit
   .comm _ZStL8__ioinit,1,1
.LC0:
   .string "Sum is: "
   .text
   .globl main
   .type main, @function
main:
.LFB1493:
.cfi_startproc
pushq %rbp
   .cfi_def_cfa_offset 16
   .cfi_offset 6, -16
   movq %rsp, %rbp
   .cfi_def_cfa_register 6
   subq $16, %rsp
   movl $50, -12(%rbp)
   movl $60, -8(%rbp)
   movl -12(%rbp), %edx
   movl -8(%rbp), %eax
   addl %edx, %eax
   movl %eax, -4(%rbp)
   leaq .LC0(%rip), %rsi
   leaq _ZSt4cout(%rip), %rdi
   call _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc@PLT
   movq %rax, %rdx
   movl -4(%rbp), %eax
   movl %eax, %esi
   movq %rdx, %rdi
   call _ZNSolsEi@PLT
   movq %rax, %rdx
   movq
_ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_@GOTPCREL(%rip),
   %rax
   movq %rax, %rsi
   movq %rdx, %rdi
   call _ZNSolsEPFRSoS_E@PLT
   movl $0, %eax
   leave
   .cfi_def_cfa 7, 8
   ret
   .cfi_endproc
.LFE1493:
   .size main, .-main
   .type _Z41__static_initialization_and_destruction_0ii, @function
_Z41__static_initialization_and_destruction_0ii:
.LFB1982:
   .cfi_startproc
   pushq %rbp
   .cfi_def_cfa_offset 16
   .cfi_offset 6, -16
   movq %rsp, %rbp
   .cfi_def_cfa_register 6
   subq $16, %rsp
   movl %edi, -4(%rbp)
   movl %esi, -8(%rbp)
   cmpl $1, -4(%rbp)
   jne .L5
   cmpl $65535, -8(%rbp)
   jne .L5
   leaq _ZStL8__ioinit(%rip), %rdi
   call _ZNSt8ios_base4InitC1Ev@PLT
   leaq __dso_handle(%rip), %rdx
   leaq _ZStL8__ioinit(%rip), %rsi
   movq _ZNSt8ios_base4InitD1Ev@GOTPCREL(%rip), %rax
   movq %rax, %rdi
   call __cxa_atexit@PLT
.L5:
   nop
leave
   .cfi_def_cfa 7, 8
   ret
   .cfi_endproc
.LFE1982:
   .size _Z41__static_initialization_and_destruction_0ii,
.-_Z41__static_initialization_and_destruction_0ii
.type _GLOBAL__sub_I_main, @function
_GLOBAL__sub_I_main:
.LFB1983:
   .cfi_startproc
   pushq %rbp
   .cfi_def_cfa_offset 16
   .cfi_offset 6, -16
   movq %rsp, %rbp
   .cfi_def_cfa_register 6
   movl $65535, %esi
   movl $1, %edi
   call _Z41__static_initialization_and_destruction_0ii
   popq %rbp
   .cfi_def_cfa 7, 8
   ret
   .cfi_endproc
.LFE1983:
   .size _GLOBAL__sub_I_main, .-_GLOBAL__sub_I_main
   .section .init_array,"aw"
   .align 8
   .quad _GLOBAL__sub_I_main
   .hidden __dso_handle
   .ident "GCC: (Ubuntu 7.3.0-16ubuntu3) 7.3.0"
   .section .note.GNU-stack,"",@progbits