cDAC: ICorDebugThread::GetActiveFrame returns 0x8007000B (ERROR_BAD_FORMAT) during managed debugging on Windows x64

[steveisok]

With cDAC enabled (DOTNET_ENABLE_CDAC=1), ICorDebug stack inspection fails on Windows x64. When a debugger services a breakpoint callback and walks the stack, ICorDebugThread::GetActiveFrame returns HRESULT 0x8007000B (HRESULT_FROM_WIN32(ERROR_BAD_FORMAT)), which surfaces to managed callers as BadImageFormatException. The debuggee process is then torn down (exit code -2146232797 / 0x8007000B).

Without cDAC the identical scenario succeeds — this is cDAC-specific.

Repro / signal

• Runtime: 11.0.0-preview.6.26311.113, Windows x64
• Env: DOTNET_ENABLE_CDAC=1
• A breakpoint is hit; on the callback thread the stackwalk path (GetActiveFrame → frame enumeration) returns 0x8007000B.

BadImageFormatException: An attempt was made to load a program with an incorrect format. (0x8007000B)
   at Marshal.ThrowExceptionForHR(...)
   at ICorDebugThread.GetActiveFrame(...)

Impact

Reproduces across ~15 independent managed-debugging scenarios (Edit-and-Continue apply-and-continue, dynamic/delegate value inspection). The same runtime build passes all of these scenarios with cDAC disabled; enabling cDAC fails them.

Expected

cDAC GetActiveFrame/stackwalk returns the active frame with S_OK, matching the legacy DAC behavior.

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