kernelbase: Do not start the debugger if SEM_NOGPFAULTERRORBOX is set.

Motor City Online apparently checks for a debugger by setting this flag and then intentionally causing a page fault. If no debugger is present on Windows, the subprocess simply dies without spawning any crash dialog. This patch emulates that behaviour, suppressing a (harmless) crash dialog from winedbg. This may result in legitimate failures no longer triggering a winedbg crash dialog, if other programs happen to use SEM_NOGPFAULTERRORBOX, but the winedbg crash dialog cannot be relied upon anyway.

kernelbase: Do not start the debugger if SEM_NOGPFAULTERRORBOX is set.
61b88ebd · Zebediah Figura · Alexandre Julliard · 8653ed03 · 61b88ebd
Commit 61b88ebd authored Nov 30, 2023 by Zebediah Figura Committed by Alexandre Julliard Apr 25, 2024
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debug.c dlls/kernelbase/debug.c +2 -3

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--- a/dlls/kernelbase/debug.c
+++ b/dlls/kernelbase/debug.c
@@ -761,9 +761,8 @@ LONG WINAPI UnhandledExceptionFilter( EXCEPTION_POINTERS *epointers )
            if (ret != EXCEPTION_CONTINUE_SEARCH) return ret;
        }
-        /* FIXME: Should check the current error mode */
+        if ((GetErrorMode() & SEM_NOGPFAULTERRORBOX) ||
+            !start_debugger_atomic( epointers ) || !NtCurrentTeb()->Peb->BeingDebugged)
-        if (!start_debugger_atomic( epointers ) || !NtCurrentTeb()->Peb->BeingDebugged)
            return EXCEPTION_EXECUTE_HANDLER;
    }
    return EXCEPTION_CONTINUE_SEARCH;