Re: Unhandled exception

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From: Noël Danjou (noel_at_noeld.com)
Date: 04/21/04 

Date: Wed, 21 Apr 2004 17:12:28 +0200

Hi Gary,

Thanks for reviewing this thread.

Just like you I don't trust the "workaround" though each time the ASSERT
line is present the exception does not occur!

By the way I recompiled the whole code with BoundsChecker (BC) 7.2 and tried
again, the same behavior happens and BC does not report any stack corruption
or overrun. Now I recompiled the whole code w/o BC.

I identified the exact line in the disassembly which causes the problem
though I still don't understand why.

Here is what happens when I put the ASSERT line and the code works:

BOOL CWebRequest::SaveResponse(LPCTSTR pszFileName)
{

ebp = 12f998

004FB330 push ebp

esp = 12f964

004FB331 mov ebp,esp
004FB333 push 0FFFFFFFFh

esp = 12f960

004FB335 push offset
__ehhandler$?SaveResponse@CWebRequest@@QAEHPBD@Z (669A16h)

esp = 12f95c

004FB33A mov eax,dword ptr fs:[00000000h]
004FB340 push eax

esp = 12f958

004FB341 mov dword ptr fs:[0],esp
004FB348 push ecx

esp = 12f954

004FB349 sub esp,80h

esp = 12f8d4 -> expected and the remaining of the code is correctly executed

Now same code without the ASSERT line:

BOOL CWebRequest::SaveResponse(LPCTSTR pszFileName)
{

ebp = 12f998

004FB330 push ebp

esp = 12f964

004FB331 mov ebp,esp
004FB333 push 0FFFFFFFFh

esp = 12f960

004FB335 push offset
__ehhandler$?SaveResponse@CWebRequest@@QAEHPBD@Z (669A16h)

esp = 12f95c

004FB33A mov eax,dword ptr fs:[00000000h]
004FB340 push eax

esp = 12f958

004FB341 mov dword ptr fs:[0],esp
004FB348 push ecx

esp = 12f954

004FB349 sub esp,80h

esp = ff46f888 -> wrong hence unhandled exception

Unhandled exception at 0x004fb32f in TestApp.exe: 0xC0000005: Access
violation writing location 0xff46f884.

The question is why the sub operation fails????

Unfortunately I cannot upload the code to the public server because it is
part of a big application which cannot be published.

If something can be made through application sharing, remote assistance or
any other method please does not hesitate to contact me through my real
e-mail address. Thank you.

Best regards, 

-- 
Noël
http://noeld.com

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