__debugbreak() without connecting windbg

Question

__debugbreak() statement in a KMD results in a BSOD, if WinDbg is not connect. I want to understand why?

I'm thinking the DUT and debugger exchange some artifacts..?

Answer 1

The __debugbreak intrinsic raises a breakpoint exception. (int 3 on x86 systems)

Without a debugger, this goes unhandled, which will result in a bugcheck.

If you'd like to detect the presence of a kernel debugger, the KD_DEBUGGER_NOT_PRESENT variable might be of use to you.

KD_DEBUGGER_NOT_PRESENT isn't always up to date, but it can be refreshed using KdRefreshDebuggerNotPresent().

You might need something like this:

void BreakIfDebuggerPresent()
{
    if (!KdRefreshDebuggerNotPresent()) {
        DbgBreakPoint();
    }
}