GCC assembler output in intel syntax

Assuming you use gcc you have a flag called -masm=dialect

From the manual of gcc:

-masm=dialect
       Output assembly instructions using selected dialect.  Also
       affects which dialect is used for basic "asm" and extended "asm".
       Supported choices (in dialect order) are att or intel. The
       default is att. Darwin does not support intel.

To get a intel syntax you have to compile with

gcc -S -masm=intel adder.c

Here I have a small example:

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
    int a = atoi(argv[1]), b = atoi(argv[2]);
    int sum=0;

    sum = a+b;
    printf("%d + %d = %d\n", a, b, sum);

    return 0;
 }

Save this as adder.c and compile it

gcc adder.c -o adder 

and test the program with

./adder 1 4

The output should be

1 + 4 = 5

Now make an intel asm file with

gcc -S  -masm=intel adder.c

Here the first lines of adder.s

.file   "adder.c"
    .intel_syntax noprefix
    .text
    .section    .rodata
.LC0:
     .string    "%d + %d = %d\n"
     .text
     .globl main
     .type  main, @function
main:
.LFB5:
    .cfi_startproc
    push    rbp
    .cfi_def_cfa_offset 16
    .cfi_offset 6, -16
    mov rbp, rsp
    .cfi_def_cfa_register 6
    sub rsp, 32
    mov DWORD PTR -20[rbp], edi
    mov QWORD PTR -32[rbp], rsi
    mov rax, QWORD PTR -32[rbp]
    add rax, 8
    mov rax, QWORD PTR [rax]

Using intel syntax in GDB

Now compile the last example with debug option:

gcc -g adder.c -o adder

Open gnu debugger

gdb -q --args ./adder 3 5 

and set the flavor

set disassembly-flavor intel

set a break at main

b main

and run the program

r

If you type now

disassemble

you will get the code in intel style:

(gdb) disassemble 
Dump of assembler code for function main:
   0x000055555555468a <+0>:     push   rbp
   0x000055555555468b <+1>:     mov    rbp,rsp
   0x000055555555468e <+4>:     sub    rsp,0x20
   0x0000555555554692 <+8>:     mov    DWORD PTR [rbp-0x14],edi
   0x0000555555554695 <+11>:    mov    QWORD PTR [rbp-0x20],rsi
=> 0x0000555555554699 <+15>:    mov    rax,QWORD PTR [rbp-0x20]
   0x000055555555469d <+19>:    add    rax,0x8
   0x00005555555546a1 <+23>:    mov    rax,QWORD PTR [rax]

To set your flavor back you have to change it back to at&t style:

set disassembly-flavor att

• To permanently get intel syntax in your gdb, type the following in your shell:

  echo "set disassembly-flavor intel" >> ~/.gdbinit
  

This will set the property to your .gdbinit file. To change simply edit this file.