[solved] 64 bits error movabs

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Roman

Joined: 21 Apr 2012
Posts: 1618

Roman 27 Aug 2020, 13:17

I read exist asm command movabs
Godbolt.org get in asm code movabs.

And this give:
movabs rdx,'012345678'

But fasm 1.73 get error illegal instruction

Last edited by Roman on 27 Aug 2020, 13:25; edited 1 time in total

27 Aug 2020, 13:17

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 19876
Location: In your JS exploiting you and your system

revolution 27 Aug 2020, 13:19

Is it in the Intel manual?

27 Aug 2020, 13:19

Roman

Joined: 21 Apr 2012
Posts: 1618

Roman 27 Aug 2020, 13:22

I found this explanation
https://reverseengineering.stackexchange.com/questions/2627/what-is-the-meaning-of-movabs-in-gas-x86-att-syntax/2628

27 Aug 2020, 13:22

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 19876
Location: In your JS exploiting you and your system

revolution 27 Aug 2020, 13:26

Is it in the Intel manual? Because stackexchange is not a source for Intel instructions.

27 Aug 2020, 13:26

Roman

Joined: 21 Apr 2012
Posts: 1618

Roman 27 Aug 2020, 14:52

site godbolt.org
c++
long long fermat() {
long long a = 0xff00ff00ff00ff00;
return a;
}
Get x64 msvc 19 wine

Code:

mov     rax, -71777214294589696             ; ff00ff00ff00ff00H
        mov     QWORD PTR a$[rsp], rax
        mov     rax, QWORD PTR a$[rsp]

Get gcc compiler

Code:

movabs  rax, -71777214294589696

27 Aug 2020, 14:52

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 19876
Location: In your JS exploiting you and your system

revolution 27 Aug 2020, 14:54

Is it in the Intel manual? It just looks like an ordinary mov.

27 Aug 2020, 14:54

Roman

Joined: 21 Apr 2012
Posts: 1618

Roman 27 Aug 2020, 15:05

I think its some psevdo asm command.
And how i read movabs do usual mov

27 Aug 2020, 15:05

Roman

Joined: 21 Apr 2012
Posts: 1618

Roman 27 Aug 2020, 15:07

When i see movabs i think do this:

Code:

movabs rdx,'01234567' ;this good for compare 8 text symbols !
cmp rdx,[Text]
jz .findText

Because i think movabs work like mov, but load in rdx 64 bits number

27 Aug 2020, 15:07

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 19876
Location: In your JS exploiting you and your system

revolution 27 Aug 2020, 15:14

And still the unanswered question: Is it in the Intel manual? Razz

27 Aug 2020, 15:14

Roman

Joined: 21 Apr 2012
Posts: 1618

Roman 27 Aug 2020, 15:53

I dont know !
I only read about movabs and try to do this in Fasm.

27 Aug 2020, 15:53

Furs

Joined: 04 Mar 2016
Posts: 2347

Furs 27 Aug 2020, 19:24

movabs is the 64-bit move. Just write:

Code:

mov rax, 0xc001c0dedeadbeef

27 Aug 2020, 19:24

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 19876
Location: In your JS exploiting you and your system

revolution 28 Aug 2020, 04:12

Code:

movabs equ mov

Fixed.

28 Aug 2020, 04:12

bitRAKE

Joined: 21 Jul 2003
Posts: 3892
Location: vpcmipstrm

bitRAKE 28 Aug 2020, 13:21

FYI: https://gcc.godbolt.org/ supports the Intel compiler as well, called ICC in the dropdown. It'll save a lot of head bumping to see the correct instruction mnemonics.

https://gcc.godbolt.org/z/evMGqh

28 Aug 2020, 13:21

MaoKo

Joined: 07 May 2019
Posts: 99
Location: Paris/French

MaoKo 28 Aug 2020, 19:10

There is also a specific register to gnu as which is eiz. Eiz is not in the Intel man and it's equivalent to 0.

Code:

; as
lea 0x00(%esi,%eiz,0x01),%esi
; fasm
eiz equ 0x00
lea esi, dword [esi+eiz*0x01]

28 Aug 2020, 19:10

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