AT&T syntax help?

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Artlav

Joined: 23 Dec 2004
Posts: 188
Location: Moscow, Russia

Artlav 22 Apr 2010, 14:40

What do following AT&T-style commands mean?

Code:

movw (0xfff3), %ax
movb $0x00, (%bx,%di)
movw -3(%bx,%si), %ax
ljmp $0xe342, $0xebe0
jmp *-22(%bp,%di)
ljmp *-24(%bp,%si)

For what i could find, first 4 translate like that:

Code:

mov ax,word [0fff3h]
mov byte [bx+di],0
mov ax,word [bx+si-3]
jmp 0e342h:0ebe0h

But i'm not sure since i can't find anything definitive on that syntax, nor have any idea what the last two jmp's mean.

Help please?

22 Apr 2010, 14:40

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20344
Location: In your JS exploiting you and your system

revolution 22 Apr 2010, 14:47

I guess:

Code:

jmp near[bp+di-22]
jmp far[bp+si-24]

22 Apr 2010, 14:47

Artlav

Joined: 23 Dec 2004
Posts: 188
Location: Moscow, Russia

Artlav 22 Apr 2010, 16:03

That worked, thank you.

22 Apr 2010, 16:03

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20344
Location: In your JS exploiting you and your system

revolution 22 Apr 2010, 16:05

This "jmp 0e342h:0ebe0h" may be the opposite "jmp 0ebe0h:0e342h"? Best if you check it thoroughly.

22 Apr 2010, 16:05

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr 22 Apr 2010, 16:36

Artlav,

Sun's x86 Assembly Language Reference Manual is my source of information about as AT&T syntax, yet it lacks ljmp mnemonic Wink

. Older Solaris 2.5 manual contains it. ljmp $0xe342, $0xebe0 is jmp 0e342h:0ebe0h, that's correct.

22 Apr 2010, 16:36

edfed

Joined: 20 Feb 2006
Posts: 4341
Location: Now

edfed 22 Apr 2010, 17:58

AT&T syntax is the reason why C exists...
it was so boring to code with that they prefered invent a HLL. Laughing

22 Apr 2010, 17:58

rugxulo

Joined: 09 Aug 2005
Posts: 2341
Location: Usono (aka, USA)

rugxulo 22 Apr 2010, 21:03

It seems people often can't understand AT&T, but here's a trick that may help:

Code:

c:\tmp>djgpp
4.42

c:\tmp [ DJGPP ] >as artlav.s

c:\tmp [ DJGPP ] >objdump -d -M intel a.out

a.out:     file format coff-go32


Disassembly of section .text:

00000000 <.text>:
   0:   66 a1 f3 ff 00 00       mov    ax,ds:0xfff3
   6:   67 c6 01 00             addr16 mov BYTE PTR [bx+di],0x0
   a:   67 66 8b 40 fd          addr16 mov ax,WORD PTR [bx+si-0x3]
   f:   ea e0 eb 00 00 42 e3    jmp    0xe342:0xebe0
  16:   67 ff 63 ea             addr16 jmp DWORD PTR [bp+di-0x16]
  1a:   67 ff 6a e8             addr16 jmp FWORD PTR [bp+si-0x18]
  1e:   90                      nop
  1f:   90                      nop

22 Apr 2010, 21:03

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