Confusing jne...

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revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17279
Location: In your JS exploiting you and your system

revolution

JohnFound wrote:

If we suppose Windows is buggy (it is possible of course) why you think it will return exactly -1??? The buggy GetMessage can return everything (in EAX and [msg] as well), so processing this kind of errors is impossible by default.

Not necessarily. GetMessage may call a number of other functions and perhaps if one of those functions fails (and/or is buggy) then GetMessage will return the error of -1.

29 Feb 2012, 12:03

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4633
Location: Argentina

LocoDelAssembly

http://msdn.microsoft.com/en-us/library/aa383751%28v=vs.85%29.aspx

Quote:

BOOL

A Boolean variable (should be TRUE or FALSE).

This type is declared in WinDef.h as follows:

typedef int BOOL;
BOOLEAN

A Boolean variable (should be TRUE or FALSE).

This type is declared in WinNT.h as follows:

typedef BYTE BOOLEAN;
BYTE

A byte (8 bits).

This type is declared in WinDef.h as follows:

typedef unsigned char BYTE;

It says "should be", but not "must be" Wink

JohnFound, I think that the documentation leaves the possibility for other kinds of errors open:

Quote:

If there is an error, the return value is -1. *For example, the function fails if hWnd is an invalid window handle or lpMsg is an invalid pointer. To get extended error information, call GetLastError.

* i.e. it is commenting about ONE possible source of error, but doesn't tell it is the only one possible.

29 Feb 2012, 15:10

Alphonso

Joined: 16 Jan 2007
Posts: 294

Alphonso

revolution wrote:

Since we are wasting time trying to optimise this, then let's do it properly.
Code:
...
  test eax,eax
  jz end_loop
  js error_handler
...    

What about when eax =0x80000000 to 0xfffffffe ?

What if you just test for -1, ignore eax = 0 and process WM_QUIT outside the loop?

29 Feb 2012, 17:59

shutdownall

Joined: 02 Apr 2010
Posts: 518
Location: Munich

shutdownall

mindcooler wrote:

@shutdownall
"handle the error and possibly exit"

Yes possibly exit.
It depends on the error.
It is not fine if a program autocloses (possibly exit = WM_QUIT in your example) with no hint at all. In this case there is no difference between a crash. At least program should give a MessageBox to alert the autoclose due to an error. Maybe give someone the chance to save some modified data. Or maybe program could stop and cleanup some other processes which may cause data loss or something. Wink

29 Feb 2012, 21:58

mindcooler

Joined: 01 Dec 2009
Posts: 423
Location: Västerås, Sweden

mindcooler

Well, as I don't know what could possibly cause a such an error in my program, I don't have a strategy for recovery, so I just make it quit. It is as good indication as anything else for my purposes. As the others are saying, the most probably cause for getting an error like this is errors in the parameters, and I don't have any programs that deal with savable data yet Smile

29 Feb 2012, 22:46

shutdownall

Joined: 02 Apr 2010
Posts: 518
Location: Munich

shutdownall

mindcooler wrote:

and I don't have any programs that deal with savable data yet

When you have, you should take care of data. Maybe an editor is crashing, would be nice to have at least a copy of the contents before quitting program. This could be done in a temporary file and let the user decide after, if content seems to be valid or not.

One example is the firefox browser with tabbed browsing. Not long time ago I closed accidently a tab with some well typed text in a window on a website (forum). That was at least half an hour of work. The function "restore closed tab" saved my ass in this way. Wink

01 Mar 2012, 01:20

JohnFound

Joined: 16 Jun 2003
Posts: 3500
Location: Bulgaria

JohnFound

Code:

        xor     eax, eax
        jz      continue

; what if the CPU have bug in the ALU?
; Handle the error and exit!
        call    [ExitProcess]


continue:

01 Mar 2012, 06:11

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17279
Location: In your JS exploiting you and your system

revolution

JohnFound wrote:

Code:

        xor     eax, eax
        jz      continue

; what if the CPU have bug in the ALU?
; Handle the error and exit!
        call    [ExitProcess]


continue:

Heh, funny you should mention this. Some time back I used to work on Olivetti systems that had discrete TTL chips making up the CPU. And the test code was pretty much exactly that. Checking that all the various gates were functioning correctly. Even things like checking that the IP register could advance properly and handle the propagation of the carry to the next bit etc. Such memories are sometimes nice to recall, even though testing like that has long since become a thing of the past.

01 Mar 2012, 06:47

mindcooler

Joined: 01 Dec 2009
Posts: 423
Location: Västerås, Sweden

mindcooler

shutdownall wrote:

mindcooler wrote:
and I don't have any programs that deal with savable data yet

When you have, you should take care of data. Maybe an editor is crashing, would be nice to have at least a copy of the contents before quitting program.

When I have data, it's easy to change to jmp dumpandquit, which is a call save and ret. And/or use autosave.

Still, I'm unsure if I'm ever going to see the error in my lifetime Razz

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01 Mar 2012, 12:49

shutdownall

Joined: 02 Apr 2010
Posts: 518
Location: Munich

shutdownall

mindcooler wrote:

Still, I'm unsure if I'm ever going to see the error in my lifetime

I wouldn't bet on it. We are talking about MS software. Cool

01 Mar 2012, 15:57

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