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Q241856: PRB: Crash in DllMain After FreeLibrary is Called on a Resource

Article: Q241856
Product(s): Microsoft C Compiler
Version(s): 4.0,4.2,5.0,6.0
Operating System(s): 
Keyword(s): kbDLL kbResource kbDSupport kbGrpDSMFCATL
Last Modified: 18-JUN-2002

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The information in this article applies to:

- Microsoft Visual C++, version 4.0 
- Microsoft Visual C++, 32-bit Enterprise Edition, versions 4.2, 5.0, 6.0 
- Microsoft Visual C++, 32-bit Professional Edition, versions 4.2, 5.0, 6.0 
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
- Microsoft Visual C++.NET (2002) 
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SYMPTOMS
========

You may receive an access violation in DllMain after unloading a DLL using the
FreeLibrary() API call.

CAUSE
=====

The DLL was a resource DLL with no entry point. The crash did not occur
immediately after the FreeLibrary() call, but rather later on. The resource DLL
was loaded either by LoadLibrary() or with LoadLibraryEx() with the last
parameter set to 0.

RESOLUTION
==========

The resource DLL should be loaded with LoadLibraryEx() instead and with the last
parameter set to LOAD_LIBRARY_AS_DATAFILE.

STATUS
======

This behavior is by design.

MORE INFORMATION
================

A resource DLL does not have an entry point. You can verify that a DLL is
resource-only by viewing the DLL import headers using the dumpbin utility that
ships with Visual C++. You can use the following command from a command prompt
to generate a text file for examination:

  dumpbin /headers mydll.dll > examine.txt

After running the above command, the text file Examine.txt is generated. If you
open Examine.txt in a text editor, you can verify a DLL is a resource DLL by
examining the value of RVA of entry point entry under the Optional Header Values
section. If it is set to zero, then the DLL is a resource-only DLL.


REFERENCES
==========

  Q202197 BUG: Freeing Resource DLLs in ExitInstance Causes Error

Additional query words: Access Violation Win95 localize resources

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Keywords          : kbDLL kbResource kbDSupport kbGrpDSMFCATL 
Technology        : kbVCsearch kbVC400 kbAudDeveloper kbVC420 kbVC500 kbVC600 kbVC32bitSearch kbVCNET kbVC500Search
Version           : :4.0,4.2,5.0,6.0
Issue type        : kbprb

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