The next patch will want to add a global variable to
PlatformDebugLibIoPort, but this is not suitable for the SEC
phase, because SEC runs from read-only flash.  The solution is
to have two library instances, one for SEC and another
for all other firmware phases.  This patch adds the "plumbing"
for the SEC library instance, separating the INF files and
moving the constructor to a separate C source file.

Contributed-under: TianoCore Contribution Agreement 1.1
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen (Intel address) <jordan.l.justen@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 OvmfPkg/Library/PlatformDebugLibIoPort/DebugLib.c  | 15 -------
 .../PlatformDebugLibIoPort/DebugLibDetect.c        | 32 +++++++++++++
 .../PlatformDebugLibIoPort/DebugLibDetectRom.c     | 32 +++++++++++++
 .../PlatformDebugLibIoPort.inf                     |  1 +
 .../PlatformRomDebugLibIoPort.inf                  | 52 ++++++++++++++++++++++
 OvmfPkg/OvmfPkgIa32.dsc                            |  2 +-
 OvmfPkg/OvmfPkgIa32X64.dsc                         |  2 +-
 OvmfPkg/OvmfPkgX64.dsc                             |  2 +-
 8 files changed, 120 insertions(+), 18 deletions(-)
 create mode 100644 OvmfPkg/Library/PlatformDebugLibIoPort/DebugLibDetect.c
 create mode 100644 OvmfPkg/Library/PlatformDebugLibIoPort/DebugLibDetectRom.c
 create mode 100644 OvmfPkg/Library/PlatformDebugLibIoPort/PlatformRomDebugLibIoPort.inf

diff --git a/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLib.c b/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLib.c
index 5435767c1c..a5572a8eeb 100644
--- a/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLib.c
+++ b/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLib.c
@@ -29,21 +29,6 @@
 //
 #define MAX_DEBUG_MESSAGE_LENGTH  0x100
 
-/**
-  This constructor function does not have to do anything.
-
-  @retval EFI_SUCCESS   The constructor always returns RETURN_SUCCESS.
-
-**/
-RETURN_STATUS
-EFIAPI
-PlatformDebugLibIoPortConstructor (
-  VOID
-  )
-{
-  return EFI_SUCCESS;
-}
-
 /**
   Prints a debug message to the debug output device if the specified error level is enabled.
 
diff --git a/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLibDetect.c b/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLibDetect.c
new file mode 100644
index 0000000000..fee908861b
--- /dev/null
+++ b/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLibDetect.c
@@ -0,0 +1,32 @@
+/** @file
+  Constructor code for QEMU debug port library.
+  Non-SEC instance.
+
+  Copyright (c) 2017, Red Hat, Inc.<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 <Uefi.h>
+
+/**
+  This constructor function does not have anything to do.
+
+  @retval EFI_SUCCESS   The constructor always returns RETURN_SUCCESS.
+
+**/
+RETURN_STATUS
+EFIAPI
+PlatformDebugLibIoPortConstructor (
+  VOID
+  )
+{
+  return EFI_SUCCESS;
+}
diff --git a/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLibDetectRom.c b/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLibDetectRom.c
new file mode 100644
index 0000000000..407fe613ff
--- /dev/null
+++ b/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLibDetectRom.c
@@ -0,0 +1,32 @@
+/** @file
+  Constructor code for QEMU debug port library.
+  SEC instance.
+
+  Copyright (c) 2017, Red Hat, Inc.<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 <Uefi.h>
+
+/**
+  This constructor function does not have to do anything.
+
+  @retval EFI_SUCCESS   The constructor always returns RETURN_SUCCESS.
+
+**/
+RETURN_STATUS
+EFIAPI
+PlatformRomDebugLibIoPortConstructor (
+  VOID
+  )
+{
+  return EFI_SUCCESS;
+}
diff --git a/OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf b/OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
index 0e74fe94cb..65d8683f1f 100644
--- a/OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
+++ b/OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
@@ -30,6 +30,7 @@
 
 [Sources]
   DebugLib.c
+  DebugLibDetect.c
 
 [Packages]
   MdePkg/MdePkg.dec
diff --git a/OvmfPkg/Library/PlatformDebugLibIoPort/PlatformRomDebugLibIoPort.inf b/OvmfPkg/Library/PlatformDebugLibIoPort/PlatformRomDebugLibIoPort.inf
new file mode 100644
index 0000000000..93763d47dd
--- /dev/null
+++ b/OvmfPkg/Library/PlatformDebugLibIoPort/PlatformRomDebugLibIoPort.inf
@@ -0,0 +1,52 @@
+## @file
+#  Instance of Debug Library for the QEMU debug console port.
+#  It uses Print Library to produce formatted output strings.
+#
+#  Copyright (c) 2006 - 2015, Intel Corporation. All rights reserved.<BR>
+#  Copyright (c) 2017, Red Hat, Inc.<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                    = 0x00010005
+  BASE_NAME                      = PlatformRomDebugLibIoPort
+  FILE_GUID                      = CEB0D9D3-328F-4C24-8C02-28FA1986AE1B
+  MODULE_TYPE                    = BASE
+  VERSION_STRING                 = 1.0
+  LIBRARY_CLASS                  = DebugLib
+  CONSTRUCTOR                    = PlatformRomDebugLibIoPortConstructor
+
+#
+#  VALID_ARCHITECTURES           = IA32 X64 IPF EBC
+#
+
+[Sources]
+  DebugLib.c
+  DebugLibDetectRom.c
+
+[Packages]
+  MdePkg/MdePkg.dec
+  OvmfPkg/OvmfPkg.dec
+
+[LibraryClasses]
+  BaseMemoryLib
+  IoLib
+  PcdLib
+  PrintLib
+  BaseLib
+  DebugPrintErrorLevelLib
+
+[Pcd]
+  gUefiOvmfPkgTokenSpaceGuid.PcdDebugIoPort                ## CONSUMES
+  gEfiMdePkgTokenSpaceGuid.PcdDebugClearMemoryValue        ## CONSUMES
+  gEfiMdePkgTokenSpaceGuid.PcdDebugPropertyMask            ## CONSUMES
+  gEfiMdePkgTokenSpaceGuid.PcdFixedDebugPrintErrorLevel    ## CONSUMES
+
diff --git a/OvmfPkg/OvmfPkgIa32.dsc b/OvmfPkg/OvmfPkgIa32.dsc
index c2f534fdbf..7ccb61147f 100644
--- a/OvmfPkg/OvmfPkgIa32.dsc
+++ b/OvmfPkg/OvmfPkgIa32.dsc
@@ -207,7 +207,7 @@
 !ifdef $(DEBUG_ON_SERIAL_PORT)
   DebugLib|MdePkg/Library/BaseDebugLibSerialPort/BaseDebugLibSerialPort.inf
 !else
-  DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
+  DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformRomDebugLibIoPort.inf
 !endif
   ReportStatusCodeLib|MdeModulePkg/Library/PeiReportStatusCodeLib/PeiReportStatusCodeLib.inf
   ExtractGuidedSectionLib|MdePkg/Library/BaseExtractGuidedSectionLib/BaseExtractGuidedSectionLib.inf
diff --git a/OvmfPkg/OvmfPkgIa32X64.dsc b/OvmfPkg/OvmfPkgIa32X64.dsc
index 9f300a2e6f..237ec71b5e 100644
--- a/OvmfPkg/OvmfPkgIa32X64.dsc
+++ b/OvmfPkg/OvmfPkgIa32X64.dsc
@@ -212,7 +212,7 @@
 !ifdef $(DEBUG_ON_SERIAL_PORT)
   DebugLib|MdePkg/Library/BaseDebugLibSerialPort/BaseDebugLibSerialPort.inf
 !else
-  DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
+  DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformRomDebugLibIoPort.inf
 !endif
   ReportStatusCodeLib|MdeModulePkg/Library/PeiReportStatusCodeLib/PeiReportStatusCodeLib.inf
   ExtractGuidedSectionLib|MdePkg/Library/BaseExtractGuidedSectionLib/BaseExtractGuidedSectionLib.inf
diff --git a/OvmfPkg/OvmfPkgX64.dsc b/OvmfPkg/OvmfPkgX64.dsc
index 1ffcf37f8b..a5047fa38e 100644
--- a/OvmfPkg/OvmfPkgX64.dsc
+++ b/OvmfPkg/OvmfPkgX64.dsc
@@ -212,7 +212,7 @@
 !ifdef $(DEBUG_ON_SERIAL_PORT)
   DebugLib|MdePkg/Library/BaseDebugLibSerialPort/BaseDebugLibSerialPort.inf
 !else
-  DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
+  DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformRomDebugLibIoPort.inf
 !endif
   ReportStatusCodeLib|MdeModulePkg/Library/PeiReportStatusCodeLib/PeiReportStatusCodeLib.inf
   ExtractGuidedSectionLib|MdePkg/Library/BaseExtractGuidedSectionLib/BaseExtractGuidedSectionLib.inf
-- 
2.14.3


_______________________________________________
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On 11/16/17 11:47, Paolo Bonzini wrote:
> The next patch will want to add a global variable to
> PlatformDebugLibIoPort, but this is not suitable for the SEC
> phase, because SEC runs from read-only flash.  The solution is
> to have two library instances, one for SEC and another
> for all other firmware phases.  This patch adds the "plumbing"
> for the SEC library instance, separating the INF files and
> moving the constructor to a separate C source file.
> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Jordan Justen (Intel address) <jordan.l.justen@intel.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  OvmfPkg/Library/PlatformDebugLibIoPort/DebugLib.c  | 15 -------
>  .../PlatformDebugLibIoPort/DebugLibDetect.c        | 32 +++++++++++++
>  .../PlatformDebugLibIoPort/DebugLibDetectRom.c     | 32 +++++++++++++
>  .../PlatformDebugLibIoPort.inf                     |  1 +
>  .../PlatformRomDebugLibIoPort.inf                  | 52 ++++++++++++++++++++++
>  OvmfPkg/OvmfPkgIa32.dsc                            |  2 +-
>  OvmfPkg/OvmfPkgIa32X64.dsc                         |  2 +-
>  OvmfPkg/OvmfPkgX64.dsc                             |  2 +-
>  8 files changed, 120 insertions(+), 18 deletions(-)
>  create mode 100644 OvmfPkg/Library/PlatformDebugLibIoPort/DebugLibDetect.c
>  create mode 100644 OvmfPkg/Library/PlatformDebugLibIoPort/DebugLibDetectRom.c
>  create mode 100644 OvmfPkg/Library/PlatformDebugLibIoPort/PlatformRomDebugLibIoPort.inf

Very nice!

I have a number of superficial comments. I've considered squashing these changes into your patch myself, but I didn't know what you'd prefer, so first I'll just list them.

> diff --git a/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLib.c b/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLib.c
> index 5435767c1c..a5572a8eeb 100644
> --- a/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLib.c
> +++ b/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLib.c
> @@ -29,21 +29,6 @@
>  //
>  #define MAX_DEBUG_MESSAGE_LENGTH  0x100
>  
> -/**
> -  This constructor function does not have to do anything.
> -
> -  @retval EFI_SUCCESS   The constructor always returns RETURN_SUCCESS.
> -
> -**/
> -RETURN_STATUS
> -EFIAPI
> -PlatformDebugLibIoPortConstructor (
> -  VOID
> -  )
> -{
> -  return EFI_SUCCESS;
> -}
> -
>  /**
>    Prints a debug message to the debug output device if the specified error level is enabled.
>  

(1) This is a pre-existent wart in the code. The return type is RETURN_STATUS, but we return EFI_SUCCESS instead of RETURN_SUCCESS.

Numerically they are the same, but the message is different. RETURN_* is for library instances that have MODULE_TYPE=BASE, meaning that they can be built into modules that are more "primitive" than DXE_DRIVERs (such as SEC, PEIM, PEI_CORE, ...). This distinction primarily influences the constructor function's parameter list -- for MODULE_TYPE=BASE library instances, it is just VOID --, but it also dictates whether we should use EFI_xxx or RETURN_xxx as status codes.

Can you please prepend a patch to the series that replaces EFI_SUCCESS with RETURN_SUCCESS in this function?

(2) Similarly, as a "precursor cleanup", <Uefi.h> should not be included anywhere in this library instance. Namely, "MdePkg/Include/Uefi.h" has the following leading comment (rewrapped here for readability):

> Root include file for Mde Package UEFI, UEFI_APPLICATION type modules.
>
> This is the include file for any module of type UEFI and
> UEFI_APPLICATION. Uefi modules only use types defined via this include
> file and can be ported easily to any environment.

UEFI_DRIVER and UEFI_APPLICATION modules are the *least* primitive module types, while this library instance is on the other end of the spectrum.

Now, "MdePkg/Include/Uefi.h" is just a convenience header for including:

#include <Uefi/UefiBaseType.h>
#include <Uefi/UefiSpec.h>

From these, "MdePkg/Include/Uefi/UefiBaseType.h" is totally fine to include wherever, while "MdePkg/Include/Uefi/UefiSpec.h" is the one that should be kept out of BASE lib classes.

Thus, in the same prepended patch, can you please also try to replace <Uefi.h> with <Uefi/UefiBaseType.h>? The lib instance should continue building just the same. (If it breaks, that means we have a layering violation in the code somewhere.)

Consequently:

> diff --git a/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLibDetect.c b/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLibDetect.c
> new file mode 100644
> index 0000000000..fee908861b
> --- /dev/null
> +++ b/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLibDetect.c
> @@ -0,0 +1,32 @@
> +/** @file
> +  Constructor code for QEMU debug port library.
> +  Non-SEC instance.
> +
> +  Copyright (c) 2017, Red Hat, Inc.<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 <Uefi.h>
> +
> +/**
> +  This constructor function does not have anything to do.
> +
> +  @retval EFI_SUCCESS   The constructor always returns RETURN_SUCCESS.
> +
> +**/
> +RETURN_STATUS
> +EFIAPI
> +PlatformDebugLibIoPortConstructor (
> +  VOID
> +  )
> +{
> +  return EFI_SUCCESS;
> +}
> diff --git a/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLibDetectRom.c b/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLibDetectRom.c
> new file mode 100644
> index 0000000000..407fe613ff
> --- /dev/null
> +++ b/OvmfPkg/Library/PlatformDebugLibIoPort/DebugLibDetectRom.c
> @@ -0,0 +1,32 @@
> +/** @file
> +  Constructor code for QEMU debug port library.
> +  SEC instance.
> +
> +  Copyright (c) 2017, Red Hat, Inc.<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 <Uefi.h>
> +
> +/**
> +  This constructor function does not have to do anything.
> +
> +  @retval EFI_SUCCESS   The constructor always returns RETURN_SUCCESS.
> +
> +**/
> +RETURN_STATUS
> +EFIAPI
> +PlatformRomDebugLibIoPortConstructor (
> +  VOID
> +  )
> +{
> +  return EFI_SUCCESS;
> +}

(3) In the above two files, <Uefi.h> should not be included, plus the constructors should return RETURN_SUCCESS.

(4) It's a bit higher up in the patch (I'm mentioning it here only for keeping the previous points focused): if you diff the two new files against each other, you get

-  This constructor function does not have anything to do.
+  This constructor function does not have to do anything.

Please consider unifying this.

Then, we get to the INF files:

> diff --git a/OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf b/OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
> index 0e74fe94cb..65d8683f1f 100644
> --- a/OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
> +++ b/OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
> @@ -30,6 +30,7 @@
>  
>  [Sources]
>    DebugLib.c
> +  DebugLibDetect.c
>  
>  [Packages]
>    MdePkg/MdePkg.dec
> diff --git a/OvmfPkg/Library/PlatformDebugLibIoPort/PlatformRomDebugLibIoPort.inf b/OvmfPkg/Library/PlatformDebugLibIoPort/PlatformRomDebugLibIoPort.inf
> new file mode 100644
> index 0000000000..93763d47dd
> --- /dev/null
> +++ b/OvmfPkg/Library/PlatformDebugLibIoPort/PlatformRomDebugLibIoPort.inf
> @@ -0,0 +1,52 @@
> +## @file
> +#  Instance of Debug Library for the QEMU debug console port.
> +#  It uses Print Library to produce formatted output strings.
> +#
> +#  Copyright (c) 2006 - 2015, Intel Corporation. All rights reserved.<BR>
> +#  Copyright (c) 2017, Red Hat, Inc.<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                    = 0x00010005
> +  BASE_NAME                      = PlatformRomDebugLibIoPort
> +  FILE_GUID                      = CEB0D9D3-328F-4C24-8C02-28FA1986AE1B
> +  MODULE_TYPE                    = BASE
> +  VERSION_STRING                 = 1.0
> +  LIBRARY_CLASS                  = DebugLib
> +  CONSTRUCTOR                    = PlatformRomDebugLibIoPortConstructor
> +
> +#
> +#  VALID_ARCHITECTURES           = IA32 X64 IPF EBC
> +#
> +
> +[Sources]
> +  DebugLib.c
> +  DebugLibDetectRom.c
> +
> +[Packages]
> +  MdePkg/MdePkg.dec
> +  OvmfPkg/OvmfPkg.dec
> +
> +[LibraryClasses]
> +  BaseMemoryLib
> +  IoLib
> +  PcdLib
> +  PrintLib
> +  BaseLib
> +  DebugPrintErrorLevelLib
> +
> +[Pcd]
> +  gUefiOvmfPkgTokenSpaceGuid.PcdDebugIoPort                ## CONSUMES
> +  gEfiMdePkgTokenSpaceGuid.PcdDebugClearMemoryValue        ## CONSUMES
> +  gEfiMdePkgTokenSpaceGuid.PcdDebugPropertyMask            ## CONSUMES
> +  gEfiMdePkgTokenSpaceGuid.PcdFixedDebugPrintErrorLevel    ## CONSUMES
> +

(5) This is totally my fault, but last night I couldn't think of it:

The LIBRARY_CLASS assignment in the [Defines] section supports a syntax that restricts the library instance to specific client module types. Such as:

  LIBRARY_CLASS                  = DebugLib|SEC
  LIBRARY_CLASS                  = DebugLib|PEI_CORE PEIM DXE_CORE DXE_DRIVER DXE_RUNTIME_DRIVER SMM_CORE DXE_SMM_DRIVER UEFI_DRIVER UEFI_APPLICATION

(The module types need not be sorted "logically" within LIBRARY_CLASS, but I did that above for a pleasing read.)

Such restrictions are helpful because then an invalid / unintended library class resolution in a DSC file is caught at build time; it won't get to cause weird behavior at runtime.

Please consider adding these lists in v3.

> diff --git a/OvmfPkg/OvmfPkgIa32.dsc b/OvmfPkg/OvmfPkgIa32.dsc
> index c2f534fdbf..7ccb61147f 100644
> --- a/OvmfPkg/OvmfPkgIa32.dsc
> +++ b/OvmfPkg/OvmfPkgIa32.dsc
> @@ -207,7 +207,7 @@
>  !ifdef $(DEBUG_ON_SERIAL_PORT)
>    DebugLib|MdePkg/Library/BaseDebugLibSerialPort/BaseDebugLibSerialPort.inf
>  !else
> -  DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
> +  DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformRomDebugLibIoPort.inf
>  !endif
>    ReportStatusCodeLib|MdeModulePkg/Library/PeiReportStatusCodeLib/PeiReportStatusCodeLib.inf
>    ExtractGuidedSectionLib|MdePkg/Library/BaseExtractGuidedSectionLib/BaseExtractGuidedSectionLib.inf
> diff --git a/OvmfPkg/OvmfPkgIa32X64.dsc b/OvmfPkg/OvmfPkgIa32X64.dsc
> index 9f300a2e6f..237ec71b5e 100644
> --- a/OvmfPkg/OvmfPkgIa32X64.dsc
> +++ b/OvmfPkg/OvmfPkgIa32X64.dsc
> @@ -212,7 +212,7 @@
>  !ifdef $(DEBUG_ON_SERIAL_PORT)
>    DebugLib|MdePkg/Library/BaseDebugLibSerialPort/BaseDebugLibSerialPort.inf
>  !else
> -  DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
> +  DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformRomDebugLibIoPort.inf
>  !endif
>    ReportStatusCodeLib|MdeModulePkg/Library/PeiReportStatusCodeLib/PeiReportStatusCodeLib.inf
>    ExtractGuidedSectionLib|MdePkg/Library/BaseExtractGuidedSectionLib/BaseExtractGuidedSectionLib.inf
> diff --git a/OvmfPkg/OvmfPkgX64.dsc b/OvmfPkg/OvmfPkgX64.dsc
> index 1ffcf37f8b..a5047fa38e 100644
> --- a/OvmfPkg/OvmfPkgX64.dsc
> +++ b/OvmfPkg/OvmfPkgX64.dsc
> @@ -212,7 +212,7 @@
>  !ifdef $(DEBUG_ON_SERIAL_PORT)
>    DebugLib|MdePkg/Library/BaseDebugLibSerialPort/BaseDebugLibSerialPort.inf
>  !else
> -  DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
> +  DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformRomDebugLibIoPort.inf
>  !endif
>    ReportStatusCodeLib|MdeModulePkg/Library/PeiReportStatusCodeLib/PeiReportStatusCodeLib.inf
>    ExtractGuidedSectionLib|MdePkg/Library/BaseExtractGuidedSectionLib/BaseExtractGuidedSectionLib.inf
> 

This is fine, but I'll use the opportunity to ask you to tweak the git config of your edk2 clone a bit :) The below hints are from <https://github.com/tianocore/tianocore.github.io/wiki/Laszlo's-unkempt-git-guide-for-edk2-contributors-and-maintainers>.

(6) Looking at the above hunks, it is not readily apparent to the reviewer what section of the DSC file is being patched. It can be improved:

(6a) run:

git config diff.ini.xfuncname '^\[[A-Za-z0-9_., ]+]'

(6b) add the following to ".git/info/attributes":

*.dec     diff=ini
*.dsc     diff=ini
*.dsc.inc diff=ini
*.fdf     diff=ini
*.fdf.inc diff=ini
*.inf     diff=ini

As a result, the hunks will look like:

> diff --git a/OvmfPkg/OvmfPkgIa32.dsc b/OvmfPkg/OvmfPkgIa32.dsc
> index c2f534fdbf3b..7ccb61147f27 100644
> --- a/OvmfPkg/OvmfPkgIa32.dsc
> +++ b/OvmfPkg/OvmfPkgIa32.dsc
> @@ -207,7 +207,7 @@ [LibraryClasses.common.SEC]
>  !ifdef $(DEBUG_ON_SERIAL_PORT)
>    DebugLib|MdePkg/Library/BaseDebugLibSerialPort/BaseDebugLibSerialPort.inf
>  !else
> -  DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf
> +  DebugLib|OvmfPkg/Library/PlatformDebugLibIoPort/PlatformRomDebugLibIoPort.inf
>  !endif
>    ReportStatusCodeLib|MdeModulePkg/Library/PeiReportStatusCodeLib/PeiReportStatusCodeLib.inf
>    ExtractGuidedSectionLib|MdePkg/Library/BaseExtractGuidedSectionLib/BaseExtractGuidedSectionLib.inf

Note "[LibraryClasses.common.SEC]" after the "@@" marker.

(Yes, we could carry a .gitattributes file in the tree, but that would require us to agree upon it.)

(7) Consider creating a file called "edk2.diff.order", with the following contents:

*.dec
*.dsc.inc
*.dsc
*.fdf.inc
*.fdf
*.inf
*.h
*.vfr
*.c

and setting the "diff.orderFile" config knob to the pathname of that file.

Then the reviewer will get to see hunks in the following order:
- package declaration file changes,
- platform DSC and flash description changes,
- module INF changes
- C header changes,
- VFR (visual form representation) changes,
- finally, C language changes.

(Yes, we could carry an order file in the tree as well, but my attempt to do it for QEMU had failed, so I didn't try posting it for edk2.)

I hope you aren't overly annoyed by the above wall of text. Do you have time for a v3?

Thank you!
Laszlo
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