I want to set my assembly debugger from at&t to intel in gcc. I'm currently on ubuntu 18.0. How can i do this?

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1 Answer

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.

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