Add lesson 56

Signed-off-by: Konstantin Aladyshev <aladyshev22@gmail.com>

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+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.
+