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diff --git a/Lessons/Lesson_56/README.md b/Lessons/Lesson_56/README.md new file mode 100644 index 0000000..1b43f9d --- /dev/null +++ b/Lessons/Lesson_56/README.md @@ -0,0 +1,84 @@ +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. + |