[NTOS:KE/EX] Add minimal EMS (headless) support for bugcheck.

In particular, the HeadlessGlobals->InBugCheck flag MUST be set prior
to displaying the blue-screen, because the HDL global lock function
would trigger a (nested) BSoD otherwise.

Regarding the unimplemented HeadlessCmdSendBlueScreenData:
it sends to the management console an XML description of the bugcheck.
An example can be seen in this issue report:
https://github.com/cloud-hypervisor/cloud-hypervisor/issues/3168

For more information, please consult:
https://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/windowsserver2003emssacxml.doc

ntoskrnl/ex/hdlsterm.c

@@ -450,8 +450,15 @@ HdlspDispatch(IN HEADLESS_CMD Command,
 
         case HeadlessCmdGetLine:
             break;
+
         case HeadlessCmdStartBugCheck:
+        {
+            HeadlessGlobals->InBugCheck = TRUE;
+            HeadlessGlobals->ProcessingCmd = FALSE;
+            Status = STATUS_SUCCESS;
             break;
+        }
+
         case HeadlessCmdDoBugCheckProcessing:
             break;
 
@@ -518,7 +525,10 @@ HdlspDispatch(IN HEADLESS_CMD Command,
         }
 
         case HeadlessCmdSendBlueScreenData:
+            // TODO: Send XML description of bugcheck.
+            // InputBuffer points to the BugCheckCode.
             break;
+
         case HeadlessCmdQueryGUID:
             break;
 

ntoskrnl/ke/bug.c

@@ -615,8 +615,20 @@ KiDisplayBlueScreen(IN ULONG MessageId,
                     IN PCHAR HardErrMessage OPTIONAL,
                     IN PCHAR Message)
 {
+    ULONG BugCheckCode = (ULONG)KiBugCheckData[0];
+    BOOLEAN Enable = TRUE;
     CHAR AnsiName[107];
 
+    /* Enable headless support for bugcheck */
+    HeadlessDispatch(HeadlessCmdStartBugCheck,
+                     NULL, 0, NULL, NULL);
+    HeadlessDispatch(HeadlessCmdEnableTerminal,
+                     &Enable, sizeof(Enable),
+                     NULL, NULL);
+    HeadlessDispatch(HeadlessCmdSendBlueScreenData,
+                     &BugCheckCode, sizeof(BugCheckCode),
+                     NULL, NULL);
+
     /* Check if bootvid is installed */
     if (InbvIsBootDriverInstalled())
     {
@@ -664,7 +676,7 @@ KiDisplayBlueScreen(IN ULONG MessageId,
     if (MessageId == BUGCODE_PSS_MESSAGE)
     {
         /* It is, so get the bug code string as well */
-        KeGetBugMessageText((ULONG)KiBugCheckData[0], NULL);
+        KeGetBugMessageText(BugCheckCode, NULL);
         InbvDisplayString("\r\n\r\n");
     }
 
@@ -683,7 +695,7 @@ KiDisplayBlueScreen(IN ULONG MessageId,
     RtlStringCbPrintfA(AnsiName,
                        sizeof(AnsiName),
                        "\r\n\r\n*** STOP: 0x%08lX (0x%p,0x%p,0x%p,0x%p)\r\n\r\n",
-                       (ULONG)KiBugCheckData[0],
+                       BugCheckCode,
                        (PVOID)KiBugCheckData[1],
                        (PVOID)KiBugCheckData[2],
                        (PVOID)KiBugCheckData[3],