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Article ID: 112335 - Last Review: January 10, 2015 - Revision: 2.0

This article was previously published under Q112335
This article has been archived. It is offered "as is" and will no longer be updated.


Building a debug version of an application containing more than 64K of type index information may cause one or more of the following error messages, depending on what version of CVPACK is being used:
CVPACK: fatal error CK1020: packed type index exceeds 65535 in module <filename.obj>
CVPACK: warning CK4009: exceeded 64K types ... discarding subsequent types.
cvpack.exe INTERNAL ERROR, exception code - 0xc0000005.


These errors are due in part to the fact that CodeView's symbolic type information index is a 16 bit value, which causes an overflow if the number of packed symbol types exceeds 64K.

Note that CK4009 is a Visual C++ version 1.0 (32-bit) and version 1.5 (16- bit) replacement for the older CK1020 error message. With CK1020, the packer failed and the program could not be debugged. With CK4009, the packer does not fail, but discards all subsequent nonprimitive types. This will at least allow the program to be debugged for those symbols whose types have not been discarded.


Here are a few things that can be done to reduce the number of symbols in an application so that it can be successfully debugged:
  1. Compile only the source files that you need to debug with /Zi and use /Zd for the rest. This will reduce the number of symbols in your application. (If you are using Programmer's WorkBench (PWB) or the Visual Workbench, it will also require you to use an external makefile, because compilation is not module selective within these tools.) If you choose to compile with /Zd, you will get line number support only for the modules. With a linker mapfile you can determine the location of your public symbols so you can at least view your global data in CodeView if needed. For additional information, please see the following article(s) in the Microsoft Knowledge Base:
    48241  ( ) Relationship between Map File Addresses and Location in Memory
  2. If you are using MFC with Visual C++, try rebuilding the MFC libraries with the /Zi switch instead of /Z7. This will build a .PDB (Program Database) file for the entire library that will contain all of the symbolic type information. While compiling the source files, each time the compiler generates type information for a new symbol, it checks the PDB file to see if this type is already present. If so, the type is not added. Using this process, the total amount of type information is reduced by eliminating redundant types that would otherwise be present in the .OBJ files created for the Microsoft Foundation Class (MFC) libraries using /Z7. Using /Zi causes redundancies to be reduced before the packer code executes, which helps the packer operate more efficiently.
  3. For Visual C++ projects, compile using /Fd to specify a single .PDB file for your application. Again, the idea here is to reduce the number of types by eliminating redundancies that are present in multi module applications before the packer executes. Note that this is automatic if you are building from the Visual Workbench. The default file will be named MSVC.PDB: using /Fd allows you to specify an alternative name. Since the default is to use PDB files (which eliminates redundant information), the problem is much less likely to occur. To enable use of the PDB, use /Zi not /Z7 when compiling, and don't turn off "Program Database" in the IDE (or use /PDB:NONE on the command line).
  4. If possible, consider eliminating some of the more complex types such as classes, structures, enums, and unions. This will reduce the likelihood of the types being redundantly included in your application.
  5. Compile some of the modules without any debugging information at all. If using the Microsoft Foundation Classes, care must be taken not to mix modules compiled with _DEBUG and modules compiled without _DEBUG. Try building the MFC library with CODEVIEW=0 or CODEVIEW=2 to reduce the amount of symbolic information (the default for DEBUG is "=1", which defines _DEBUG). When the class library is built with CODEVIEW = 0, you will not have any library debugging information available. The MFC debugging functions TRACE and ASSERT will still be available, however. With CODEVIEW=2, some components of the library will be built with debugging information. The README.TXT in ..\MFC\SRC explains further what each of the options do in terms of limiting the debugging information available for the MFC library. Additional information can also be found in the Appendix of the "Class Libraries User's Guide" as follows:
    Appendix B for Visual C++ version 1.0 (16-bit)
    Appendix A for Visual C++ version 1.5 (16-bit)
    Appendix B for Visual C++ version 1.1 (32-bit)
  6. One other unconfirmed possible solution is related to precompiled headers. You might try enabling or disabling the use of precompiled headers, whichever is not currently being used, and then rebuild everything. This may have varying effects depending on your application's use of header files.


Microsoft has confirmed this to be a problem in CVPACK utility for MS-DOS, versions 4.0, 4.1, and 4.26, and CVPACK Utility for Windows NT, version 4.25. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.


The Symbol and Type OMF Specification requires that symbolic debugging information be contained in two tables emitted by the compiler (in Visual C++ these are included in the object modules and the .PDB file). The first table is called $$SYMBOLS and describes the symbols in the object file; while the second is called $$TYPES and contains information about the symbol types. For example, the statement "int i;" defines the symbol "i" of type "int". There are fields in the records of both tables that are used to index into the records of the other table. Furthermore, there is a third table of symbolic information that is generated by the linker and written into the executable file. This table is called PUBLICS and contains the symbol records for each public symbol encountered while processing the object files.

CVPACK's purpose is to remove duplicate symbol and type information and rewrite the remaining information in a format optimized for CodeView processing. The type indices for this remaining information must not exceed 64K, because the index itself is a 16-bit value. Because this index is part of the specification, it cannot be changed without breaking the tools that depend on it, many of which are supplied by third-party vendors.

  • Microsoft CVPACK for MS-DOS 4.0
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