Introduce a variant of BaseDebugLibSerialPort that behaves correctly with
regards to the use of the serial port after ExitBootServices(). At boot
time, all DEBUG() prints and ASSERT() invocations are executed normally.
At runtime, DEBUG() prints are dropped entirely, and ASSERT()s omit the
serial output as well, and only perform the configured post-ASSERT()
action, i.e., issue a CPU breakpoint or enter a deadloop.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
---
 MdePkg/Library/DxeRuntimeDebugLibSerialPort/DebugLib.c                       | 346 ++++++++++++++++++++
 MdePkg/Library/DxeRuntimeDebugLibSerialPort/DxeRuntimeDebugLibSerialPort.inf |  55 ++++
 MdePkg/Library/DxeRuntimeDebugLibSerialPort/DxeRuntimeDebugLibSerialPort.uni |  21 ++
 3 files changed, 422 insertions(+)

diff --git a/MdePkg/Library/DxeRuntimeDebugLibSerialPort/DebugLib.c b/MdePkg/Library/DxeRuntimeDebugLibSerialPort/DebugLib.c
new file mode 100644
index 000000000000..f403b0257981
--- /dev/null
+++ b/MdePkg/Library/DxeRuntimeDebugLibSerialPort/DebugLib.c
@@ -0,0 +1,346 @@
+/** @file
+  DXE runtime Debug library instance based on Serial Port library.
+  It takes care not to call into SerialPortLib after ExitBootServices() has
+  been called, to prevent touching hardware that is no longer owned by the
+  firmware.
+
+  Copyright (c) 2006 - 2011, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2018, Linaro, Ltd. All rights reserved.<BR>
+
+  This program and the accompanying materials
+  are licensed and made available under the terms and conditions of the BSD License
+  which accompanies this distribution.  The full text of the license may be found at
+  http://opensource.org/licenses/bsd-license.php.
+
+  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
+  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+
+**/
+
+#include <Base.h>
+#include <Library/DebugLib.h>
+#include <Library/DebugPrintErrorLevelLib.h>
+#include <Library/BaseLib.h>
+#include <Library/PrintLib.h>
+#include <Library/PcdLib.h>
+#include <Library/BaseMemoryLib.h>
+#include <Library/SerialPortLib.h>
+
+STATIC EFI_EVENT      mEfiExitBootServicesEvent;
+STATIC BOOLEAN        mEfiAtRuntime;
+
+//
+// Define the maximum debug and assert message length that this library supports
+//
+#define MAX_DEBUG_MESSAGE_LENGTH  0x100
+
+/**
+  Set AtRuntime flag as TRUE after ExitBootServices.
+
+  @param[in]  Event   The Event that is being processed.
+  @param[in]  Context The Event Context.
+
+**/
+STATIC
+VOID
+EFIAPI
+ExitBootServicesEvent (
+  IN EFI_EVENT        Event,
+  IN VOID             *Context
+  )
+{
+  mEfiAtRuntime = TRUE;
+}
+
+/**
+  The constructor function to initialize the Serial Port library and
+  register a callback for the ExitBootServices event.
+
+  @param[in]  ImageHandle   The firmware allocated handle for the EFI image.
+  @param[in]  SystemTable   A pointer to the EFI System Table.
+
+  @retval EFI_SUCCESS   The operation completed successfully.
+  @retval other         Either the serial port failed to initialize or the
+                        ExitBootServices event callback registration failed.
+**/
+EFI_STATUS
+EFIAPI
+DxeRuntimeDebugLibSerialPortConstructor (
+  IN EFI_HANDLE        ImageHandle,
+  IN EFI_SYSTEM_TABLE  *SystemTable
+  )
+{
+  EFI_STATUS    Status;
+
+  Status = SerialPortInitialize ();
+  if (EFI_ERROR (Status)) {
+    return Status;
+  }
+
+  return SystemTable->BootServices->CreateEventEx (EVT_NOTIFY_SIGNAL,
+                                      TPL_NOTIFY, ExitBootServicesEvent, NULL,
+                                      &gEfiEventExitBootServicesGuid,
+                                      &mEfiExitBootServicesEvent);
+}
+
+/**
+  If a runtime driver exits with an error, it must call this routine
+  to free the allocated resource before the exiting.
+
+  @param[in]  ImageHandle   The firmware allocated handle for the EFI image.
+  @param[in]  SystemTable   A pointer to the EFI System Table.
+
+  @retval     EFI_SUCCESS       The Runtime Driver Lib shutdown successfully.
+  @retval     EFI_UNSUPPORTED   Runtime Driver lib was not initialized.
+**/
+EFI_STATUS
+EFIAPI
+DxeRuntimeDebugLibSerialPortDestructor (
+  IN EFI_HANDLE        ImageHandle,
+  IN EFI_SYSTEM_TABLE  *SystemTable
+  )
+{
+  return SystemTable->BootServices->CloseEvent (mEfiExitBootServicesEvent);
+}
+
+/**
+  Prints a debug message to the debug output device if the specified error level is enabled.
+
+  If any bit in ErrorLevel is also set in DebugPrintErrorLevelLib function
+  GetDebugPrintErrorLevel (), then print the message specified by Format and the
+  associated variable argument list to the debug output device.
+
+  If Format is NULL, then ASSERT().
+
+  @param  ErrorLevel  The error level of the debug message.
+  @param  Format      Format string for the debug message to print.
+  @param  ...         Variable argument list whose contents are accessed
+                      based on the format string specified by Format.
+
+**/
+VOID
+EFIAPI
+DebugPrint (
+  IN  UINTN        ErrorLevel,
+  IN  CONST CHAR8  *Format,
+  ...
+  )
+{
+  CHAR8    Buffer[MAX_DEBUG_MESSAGE_LENGTH];
+  VA_LIST  Marker;
+
+  if (mEfiAtRuntime) {
+    return;
+  }
+
+  //
+  // If Format is NULL, then ASSERT().
+  //
+  ASSERT (Format != NULL);
+
+  //
+  // Check driver debug mask value and global mask
+  //
+  if ((ErrorLevel & GetDebugPrintErrorLevel ()) == 0) {
+    return;
+  }
+
+  //
+  // Convert the DEBUG() message to an ASCII String
+  //
+  VA_START (Marker, Format);
+  AsciiVSPrint (Buffer, sizeof (Buffer), Format, Marker);
+  VA_END (Marker);
+
+  //
+  // Send the print string to a Serial Port
+  //
+  SerialPortWrite ((UINT8 *)Buffer, AsciiStrLen (Buffer));
+}
+
+
+/**
+  Prints an assert message containing a filename, line number, and description.
+  This may be followed by a breakpoint or a dead loop.
+
+  Print a message of the form "ASSERT <FileName>(<LineNumber>): <Description>\n"
+  to the debug output device.  If DEBUG_PROPERTY_ASSERT_BREAKPOINT_ENABLED bit of
+  PcdDebugProperyMask is set then CpuBreakpoint() is called. Otherwise, if
+  DEBUG_PROPERTY_ASSERT_DEADLOOP_ENABLED bit of PcdDebugProperyMask is set then
+  CpuDeadLoop() is called.  If neither of these bits are set, then this function
+  returns immediately after the message is printed to the debug output device.
+  DebugAssert() must actively prevent recursion.  If DebugAssert() is called while
+  processing another DebugAssert(), then DebugAssert() must return immediately.
+
+  If FileName is NULL, then a <FileName> string of "(NULL) Filename" is printed.
+  If Description is NULL, then a <Description> string of "(NULL) Description" is printed.
+
+  @param  FileName     The pointer to the name of the source file that generated the assert condition.
+  @param  LineNumber   The line number in the source file that generated the assert condition
+  @param  Description  The pointer to the description of the assert condition.
+
+**/
+VOID
+EFIAPI
+DebugAssert (
+  IN CONST CHAR8  *FileName,
+  IN UINTN        LineNumber,
+  IN CONST CHAR8  *Description
+  )
+{
+  CHAR8  Buffer[MAX_DEBUG_MESSAGE_LENGTH];
+
+  //
+  // Generate the ASSERT() message in Ascii format
+  //
+  AsciiSPrint (Buffer, sizeof (Buffer), "ASSERT [%a] %a(%d): %a\n",
+    gEfiCallerBaseName, FileName, LineNumber, Description);
+
+  if (!mEfiAtRuntime) {
+    //
+    // Send the print string to the Console Output device
+    //
+    SerialPortWrite ((UINT8 *)Buffer, AsciiStrLen (Buffer));
+  }
+
+  //
+  // Generate a Breakpoint, DeadLoop, or NOP based on PCD settings
+  //
+  if ((PcdGet8(PcdDebugPropertyMask) & DEBUG_PROPERTY_ASSERT_BREAKPOINT_ENABLED) != 0) {
+    CpuBreakpoint ();
+  } else if ((PcdGet8(PcdDebugPropertyMask) & DEBUG_PROPERTY_ASSERT_DEADLOOP_ENABLED) != 0) {
+    CpuDeadLoop ();
+  }
+}
+
+
+/**
+  Fills a target buffer with PcdDebugClearMemoryValue, and returns the target buffer.
+
+  This function fills Length bytes of Buffer with the value specified by
+  PcdDebugClearMemoryValue, and returns Buffer.
+
+  If Buffer is NULL, then ASSERT().
+  If Length is greater than (MAX_ADDRESS - Buffer + 1), then ASSERT().
+
+  @param   Buffer  The pointer to the target buffer to be filled with PcdDebugClearMemoryValue.
+  @param   Length  The number of bytes in Buffer to fill with zeros PcdDebugClearMemoryValue.
+
+  @return  Buffer  The pointer to the target buffer filled with PcdDebugClearMemoryValue.
+
+**/
+VOID *
+EFIAPI
+DebugClearMemory (
+  OUT VOID  *Buffer,
+  IN UINTN  Length
+  )
+{
+  //
+  // If Buffer is NULL, then ASSERT().
+  //
+  ASSERT (Buffer != NULL);
+
+  //
+  // SetMem() checks for the the ASSERT() condition on Length and returns Buffer
+  //
+  return SetMem (Buffer, Length, PcdGet8(PcdDebugClearMemoryValue));
+}
+
+
+/**
+  Returns TRUE if ASSERT() macros are enabled.
+
+  This function returns TRUE if the DEBUG_PROPERTY_DEBUG_ASSERT_ENABLED bit of
+  PcdDebugProperyMask is set.  Otherwise FALSE is returned.
+
+  @retval  TRUE    The DEBUG_PROPERTY_DEBUG_ASSERT_ENABLED bit of PcdDebugProperyMask is set.
+  @retval  FALSE   The DEBUG_PROPERTY_DEBUG_ASSERT_ENABLED bit of PcdDebugProperyMask is clear.
+
+**/
+BOOLEAN
+EFIAPI
+DebugAssertEnabled (
+  VOID
+  )
+{
+  return (BOOLEAN) ((PcdGet8(PcdDebugPropertyMask) & DEBUG_PROPERTY_DEBUG_ASSERT_ENABLED) != 0);
+}
+
+
+/**
+  Returns TRUE if DEBUG() macros are enabled.
+
+  This function returns TRUE if the DEBUG_PROPERTY_DEBUG_PRINT_ENABLED bit of
+  PcdDebugProperyMask is set.  Otherwise FALSE is returned.
+
+  @retval  TRUE    The DEBUG_PROPERTY_DEBUG_PRINT_ENABLED bit of PcdDebugProperyMask is set.
+  @retval  FALSE   The DEBUG_PROPERTY_DEBUG_PRINT_ENABLED bit of PcdDebugProperyMask is clear.
+
+**/
+BOOLEAN
+EFIAPI
+DebugPrintEnabled (
+  VOID
+  )
+{
+  return (BOOLEAN) ((PcdGet8(PcdDebugPropertyMask) & DEBUG_PROPERTY_DEBUG_PRINT_ENABLED) != 0);
+}
+
+
+/**
+  Returns TRUE if DEBUG_CODE() macros are enabled.
+
+  This function returns TRUE if the DEBUG_PROPERTY_DEBUG_CODE_ENABLED bit of
+  PcdDebugProperyMask is set.  Otherwise FALSE is returned.
+
+  @retval  TRUE    The DEBUG_PROPERTY_DEBUG_CODE_ENABLED bit of PcdDebugProperyMask is set.
+  @retval  FALSE   The DEBUG_PROPERTY_DEBUG_CODE_ENABLED bit of PcdDebugProperyMask is clear.
+
+**/
+BOOLEAN
+EFIAPI
+DebugCodeEnabled (
+  VOID
+  )
+{
+  return (BOOLEAN) ((PcdGet8(PcdDebugPropertyMask) & DEBUG_PROPERTY_DEBUG_CODE_ENABLED) != 0);
+}
+
+
+/**
+  Returns TRUE if DEBUG_CLEAR_MEMORY() macro is enabled.
+
+  This function returns TRUE if the DEBUG_PROPERTY_CLEAR_MEMORY_ENABLED bit of
+  PcdDebugProperyMask is set.  Otherwise FALSE is returned.
+
+  @retval  TRUE    The DEBUG_PROPERTY_CLEAR_MEMORY_ENABLED bit of PcdDebugProperyMask is set.
+  @retval  FALSE   The DEBUG_PROPERTY_CLEAR_MEMORY_ENABLED bit of PcdDebugProperyMask is clear.
+
+**/
+BOOLEAN
+EFIAPI
+DebugClearMemoryEnabled (
+  VOID
+  )
+{
+  return (BOOLEAN) ((PcdGet8(PcdDebugPropertyMask) & DEBUG_PROPERTY_CLEAR_MEMORY_ENABLED) != 0);
+}
+
+/**
+  Returns TRUE if any one of the bit is set both in ErrorLevel and PcdFixedDebugPrintErrorLevel.
+
+  This function compares the bit mask of ErrorLevel and PcdFixedDebugPrintErrorLevel.
+
+  @retval  TRUE    Current ErrorLevel is supported.
+  @retval  FALSE   Current ErrorLevel is not supported.
+
+**/
+BOOLEAN
+EFIAPI
+DebugPrintLevelEnabled (
+  IN  CONST UINTN        ErrorLevel
+  )
+{
+  return (BOOLEAN) ((ErrorLevel & PcdGet32(PcdFixedDebugPrintErrorLevel)) != 0);
+}
diff --git a/MdePkg/Library/DxeRuntimeDebugLibSerialPort/DxeRuntimeDebugLibSerialPort.inf b/MdePkg/Library/DxeRuntimeDebugLibSerialPort/DxeRuntimeDebugLibSerialPort.inf
new file mode 100644
index 000000000000..4b5157ca093c
--- /dev/null
+++ b/MdePkg/Library/DxeRuntimeDebugLibSerialPort/DxeRuntimeDebugLibSerialPort.inf
@@ -0,0 +1,55 @@
+## @file
+#  DXE runtime Debug library instance based on Serial Port library.
+#  It takes care not to call into SerialPortLib after ExitBootServices() has
+#  been called, to prevent touching hardware that is no longer owned by the
+#  firmware.
+#
+#  Copyright (c) 2006 - 2015, Intel Corporation. All rights reserved.<BR>
+#  Copyright (c) 2018, Linaro, Ltd. All rights reserved.<BR>
+#
+#  This program and the accompanying materials
+#  are licensed and made available under the terms and conditions of the BSD License
+#  which accompanies this distribution. The full text of the license may be found at
+#  http://opensource.org/licenses/bsd-license.php.
+#  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+#
+#
+##
+
+[Defines]
+  INF_VERSION                    = 0x0001001A
+  BASE_NAME                      = DxeRuntimeDebugLibSerialPort
+  MODULE_UNI_FILE                = DxeRuntimeDebugLibSerialPort.uni
+  FILE_GUID                      = 9D914E2F-7CCB-41DB-8E74-9AFF8F3BBFBF
+  MODULE_TYPE                    = DXE_RUNTIME_DRIVER
+  VERSION_STRING                 = 1.0
+  LIBRARY_CLASS                  = DebugLib|DXE_RUNTIME_DRIVER
+  CONSTRUCTOR                    = DxeRuntimeDebugLibSerialPortConstructor
+  DESTRUCTOR                     = DxeRuntimeDebugLibSerialPortDestructor
+
+#
+#  VALID_ARCHITECTURES           = AARCH64 ARM IA32 X64 IPF EBC
+#
+
+[Sources]
+  DebugLib.c
+
+[Packages]
+  MdePkg/MdePkg.dec
+
+[LibraryClasses]
+  BaseLib
+  BaseMemoryLib
+  DebugPrintErrorLevelLib
+  PcdLib
+  PrintLib
+  SerialPortLib
+
+[Guids]
+  gEfiEventExitBootServicesGuid                         ## CONSUMES ## Event
+
+[Pcd]
+  gEfiMdePkgTokenSpaceGuid.PcdDebugClearMemoryValue     ## CONSUMES
+  gEfiMdePkgTokenSpaceGuid.PcdDebugPropertyMask         ## CONSUMES
+  gEfiMdePkgTokenSpaceGuid.PcdFixedDebugPrintErrorLevel ## CONSUMES
diff --git a/MdePkg/Library/DxeRuntimeDebugLibSerialPort/DxeRuntimeDebugLibSerialPort.uni b/MdePkg/Library/DxeRuntimeDebugLibSerialPort/DxeRuntimeDebugLibSerialPort.uni
new file mode 100644
index 000000000000..cd65515c4177
--- /dev/null
+++ b/MdePkg/Library/DxeRuntimeDebugLibSerialPort/DxeRuntimeDebugLibSerialPort.uni
@@ -0,0 +1,21 @@
+// /** @file
+// Instance of Debug Library based on Serial Port Library.
+//
+// It uses Print Library to produce formatted output strings to seiral port device.
+//
+// Copyright (c) 2006 - 2014, Intel Corporation. All rights reserved.<BR>
+//
+// This program and the accompanying materials
+// are licensed and made available under the terms and conditions of the BSD License
+// which accompanies this distribution. The full text of the license may be found at
+// http://opensource.org/licenses/bsd-license.php.
+// THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
+// WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+//
+// **/
+
+
+#string STR_MODULE_ABSTRACT             #language en-US "Instance of Debug Library based on Serial Port Library"
+
+#string STR_MODULE_DESCRIPTION          #language en-US "It uses Print Library to produce formatted output strings to a serial port device."
+
-- 
2.11.0

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