Geoff Chappell, Software Analyst
The SYSTEM_KERNEL_DEBUGGER_INFORMATION structure is what a successful call to ZwQuerySystemInformation or NtQuerySystemInformation produces in its output buffer when given the information class SystemKernelDebuggerInformation (0x23).
The SYSTEM_KERNEL_DEBUGGER_INFORMATION structure is not documented.
Microsoft does publish the practical equivalent of a C-language definition as type information in public symbol files, though not for the kernel, where the structure is prepared, nor even for low-level user-mode DLLs that interpret the structure, but for various higher-level user-mode DLLs such as URLMON.DLL and only then starting with version 6.2.
Two earlier disclosures of type information are known, though not in symbol files but in statically linked libraries: GDISRVL.LIB from the Device Driver Kit (DDK) for Windows NT 3.51; and SHELL32.LIB from the DDK for Windows NT 4.0.
The SYSTEM_KERNEL_DEBUGGER_INFORMATION is 0x02 bytes in both 32-bit and 64-bit Windows.