Bug Check 0x0100

The LOADER_BLOCK_MISMATCH bug check reports that the loader and kernel disagree about their combination.

1st Argument major version of loader parameter block
2nd Argument minor version of loader parameter block
3rd Argument size of loader parameter block
4th Argument size of loader parameter extension;
else zero

A LOADER_PARAMETER_BLOCK is received from the loader as the kernel’s one argument for initialisation, and contains a pointer to a separate LOADER_PARAMETER_EXTENSION. Both structures vary greatly between Windows versions and are clearly vital. This bugcheck means that at least one of the structures does not fit the kernel’s expectations. Probably, the loader and kernel are from different Windows versions or even from different builds. The point to this bugcheck is much reduced, however, since the kernel does not try to validate the loader until it gets round to initialising the executive’s understanding of the boot processor.

Version 6.1 introduces OsMajorVersion, OsMinorVersion and Size members at the beginning of the LOADER_PARAMETER_BLOCK, and later versions keep them. Earlier versions being with a LIST_ENTRY, which is extremely unlikely to fit the version numbers and size by accident. The LOADER_PARAMETER_EXTENSION has long begun with its Size (but loses its own MajorVersion and MinorVersion in version 6.1). The location of the Extension member that points from one structure to the other varies with the Windows version. In the 32-bit builds, for instance, it is at offsets 0x64 in version 6.1, 0x74 in versions 6.2 and 6.3, and 0x84 in version 10.0.

If the kernel dislikes what it finds at the beginning of the supposed loader block, it raises this bugcheck with zero for the fourth argument (it being unsafe even to look for the supposed extension). Conversely, a non-zero fourth argument implies that the block seems sound and the mismatch is with the extension.


The LOADER_BLOCK_MISMATCH bug check can occur in version 6.1 and higher. It replaces one case of the much older MISMATCHED_HAL.

Microsoft’s documentation in the Windows Driver Kit (WDK) for Windows 7, dated June 2009, and in the contemporaneous Debugging Tools for Windows, is completely wrong about the arguments, presumably as a cut-and-paste error from documentation of MISMATCHED_HAL.