Lesson_56

In one of the previous lessons we've looked at the HII resources from the PlatformDxe module https://github.com/tianocore/edk2/blob/master/OvmfPkg/PlatformDxe. You could notice that this resources were registered with a GUID number that is not referenced neither in the package DEC file, nor in any *.c file:

PackageList[9]: GUID=D9DCC5DF-4007-435E-9098-8970935504B2; size=0x855
        Package[0]: type=FORMS; size=0x1F6
        Package[1]: type=STRINGS; size=0x62B
        Package[2]: type=DEVICE_PATH; size=0x1C
        Package[3]: type=END; size=0x4

The GUID value is identical to the value of the FILE_GUID in the module INF file https://github.com/tianocore/edk2/blob/master/OvmfPkg/PlatformDxe/Platform.inf

[Defines]
  ...
  BASE_NAME                      = PlatformDxe
  FILE_GUID                      = D9DCC5DF-4007-435E-9098-8970935504B2
  ...
  

How to get this GUID to the C code? With the EDKII build system is pretty simple. The GUID from the INF file FILE_GUID key automatically goes to the Autoconf headers along with the couple of other values https://github.com/tianocore/edk2/blob/master/BaseTools/Source/Python/AutoGen/GenC.py:

def CreateHeaderCode(Info, AutoGenC, AutoGenH):
    ...
    #
    # Publish the CallerId Guid
    #
    AutoGenC.Append('\nGLOBAL_REMOVE_IF_UNREFERENCED GUID gEfiCallerIdGuid = %s;\n' % GuidStringToGuidStructureString(Info.Guid))
    AutoGenC.Append('\nGLOBAL_REMOVE_IF_UNREFERENCED GUID gEdkiiDscPlatformGuid = %s;\n' % GuidStringToGuidStructureString(Info.PlatformInfo.Guid))
    AutoGenC.Append('\nGLOBAL_REMOVE_IF_UNREFERENCED CHAR8 *gEfiCallerBaseName = "%s";\n' % Info.Name)

You could see these values in the Build/OvmfX64/RELEASE_GCC5/X64/OvmfPkg/PlatformDxe/Platform/DEBUG/AutoGen.h:

extern GUID  gEfiCallerIdGuid;
extern GUID  gEdkiiDscPlatformGuid;
extern CHAR8 *gEfiCallerBaseName;

#define EFI_CALLER_ID_GUID \
  {0xD9DCC5DF, 0x4007, 0x435E, {0x90, 0x98, 0x89, 0x70, 0x93, 0x55, 0x04, 0xB2}}
#define EDKII_DSC_PLATFORM_GUID \
  {0x5a9e7754, 0xd81b, 0x49ea, {0x85, 0xad, 0x69, 0xea, 0xa7, 0xb1, 0x53, 0x9b}}

And in the Build/OvmfX64/RELEASE_GCC5/X64/OvmfPkg/PlatformDxe/Platform/DEBUG/AutoGen.c:

GLOBAL_REMOVE_IF_UNREFERENCED GUID gEfiCallerIdGuid = {0xD9DCC5DF, 0x4007, 0x435E, {0x90, 0x98, 0x89, 0x70, 0x93, 0x55, 0x04, 0xB2}};

GLOBAL_REMOVE_IF_UNREFERENCED GUID gEdkiiDscPlatformGuid = {0x5a9e7754, 0xd81b, 0x49ea, {0x85, 0xad, 0x69, 0xea, 0xa7, 0xb1, 0x53, 0x9b}};

GLOBAL_REMOVE_IF_UNREFERENCED CHAR8 *gEfiCallerBaseName = "PlatformDxe";

These 3 variables are present in Autoconf files for every module, including ours:

• gEfiCallerIdGuid - value of the FILE_GUID key in the module INF file,
• gEdkiiDscPlatformGuid - value of the PLATFORM_GUID key in the module package DSC file,
• gEfiCallerBaseName - value of the BASE_NAME key in the module INF file, encoded in ASCII string

You can see that the gEfiCallerIdGuid is really used in the https://github.com/tianocore/edk2/blob/master/OvmfPkg/PlatformDxe/Platform.c:

EFI_STATUS
EFIAPI
PlatformInit (
  IN  EFI_HANDLE        ImageHandle,
  IN  EFI_SYSTEM_TABLE  *SystemTable
  )
  ...
  mInstalledPackages = HiiAddPackages (
                         &gEfiCallerIdGuid,  // PackageListGuid
                         ImageHandle,        // associated DeviceHandle
                         PlatformDxeStrings, // 1st package
                         PlatformFormsBin,   // 2nd package
                         NULL                // terminator
                         );
  ...

It doesn't look like gEdkiiDscPlatformGuid is used anywhere in the EDKII codebase, but you could use it if you want in the same way like any other GUID.

As for the gEfiCallerBaseName it is often used in the debug prints:

DEBUG ((DEBUG_ERROR, "%a: %a: MyFunction(): %r\n",  gEfiCallerBaseName, __FUNCTION__, Status));

As the gEfiCallerBaseName string is encoded in ASCII (=CHAR8*), to print it it is necessary to use %a formatting.