From 017a590ec6c14e0f5366efd4da9be444b3e62809 Mon Sep 17 00:00:00 2001 From: Konstantin Aladyshev Date: Sat, 10 Jul 2021 01:31:32 +0300 Subject: Add lesson 36 Signed-off-by: Konstantin Aladyshev --- Lessons/Lesson_36/README.md | 157 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 157 insertions(+) create mode 100644 Lessons/Lesson_36/README.md (limited to 'Lessons/Lesson_36/README.md') diff --git a/Lessons/Lesson_36/README.md b/Lessons/Lesson_36/README.md new file mode 100644 index 0000000..f6d64ad --- /dev/null +++ b/Lessons/Lesson_36/README.md @@ -0,0 +1,157 @@ +In this lesson we will try to create the most simple library. + +Usually libraries are present in these directories: +``` +/Library// <---- inf and source files for the library (=library implementation) +/Include/Library/ <---- library headers (=library interface) +``` + +Create folders for our `SimpleLibrary`: +``` +$ mkdir -p UefiLessonsPkg/Library/SimpleLibrary/ +$ mkdir -p UefiLessonsPkg/Include/Library/ +``` + +First let's implement the header file, the interface for our library. Our `SimpleLibrary` would contain the only function `Plus2` that would receive a `number` and return a `number+2`. +Therefore the content in the header file (`UefiLessonsPkg/Include/Library/SimpleLibrary.h`) would look like this: +``` +UINTN Plus2(UINTN number); +``` + +No harder the library implementation file `UefiLessonsPkg/Library/SimpleLibrary/SimpleLibrary.c`: +``` +#include + +UINTN Plus2(UINTN number) { + return number+2; +} +``` + +This is really a simple library, it stands to its name! + +Now we need to create an INF file for the library `UefiLessonsPkg/Library/SimpleLibrary/SimpleLibrary.inf`: +``` +[Defines] + INF_VERSION = 1.25 + BASE_NAME = SimpleLibrary + FILE_GUID = 826c8951-5bd2-4d72-a9d9-f7ab48684117 + MODULE_TYPE = UEFI_APPLICATION + VERSION_STRING = 1.0 + LIBRARY_CLASS = SimpleLibrary | UEFI_APPLICATION + +[Sources] + SimpleLibrary.c + +[Packages] + MdePkg/MdePkg.dec +``` + +The interesting string here is the: +``` +LIBRARY_CLASS = SimpleLibrary | UEFI_APPLICATION +``` +It says that this library can only be used in modules with a type `UEFI_APPLICATION`. If you would say here `DXE_DRIVER` and try to link it to some of you UEFI applications, build process would fail. The error message would look like this: +``` +build.py... +/home/kostr/tiano/edk2/UefiLessonsPkg/UefiLessonsPkg.dsc(...): error 1001: Module type [UEFI_APPLICATION] is not supported by library instance [/home/kostr/tiano/edk2/UefiLessonsPkg/Library/SimpleLibrary/SimpleLibrary.inf] + consumed by [/home/kostr/tiano/edk2/UefiLessonsPkg/] +``` + +Now we need to include our library to our package DSC file `UefiLessonsPkg/UefiLessonsPkg.dsc`, so it would get build on a package build: +``` +[Components] + ... + UefiLessonsPkg/Library/SimpleLibrary/SimpleLibrary.inf +``` + +But if you try to build our package now build would fail with a message: +``` +/home/kostr/tiano/edk2/UefiLessonsPkg/Library/SimpleLibrary/SimpleLibrary.c:1:10: fatal error: Library/SimpleLibrary.h: No such file or directory + 1 | #include + | ^~~~~~~~~~~~~~~~~~~~~~~~~ +compilation terminated. +``` +The reason of that is a fact that our `UefiLessonsPkg/Include/Library/` folder is not recognized by a build system as a place where headers might be. + +To fix it we need to add to our `UefiLessonsPkg/UefiLessonsPkg.dec` file `[Includes]` section: +``` +[Includes] + Include +``` + +And include this `UefiLessonsPkg/UefiLessonsPkg.dec` file to the library module INF file section `[Packages]`: +``` +[Packages] + MdePkg/MdePkg.dec + UefiLessonsPkg/UefiLessonsPkg.dec +``` + +Now we are good, build would succeed. + +# SimpleLibraryUser + +Now let's create an application that would use our library. + +UefiLessonsPkg/SimpleLibraryUser/SimpleLibraryUser.c: +``` +#include +#include + +#include + +EFI_STATUS +EFIAPI +UefiMain ( + IN EFI_HANDLE ImageHandle, + IN EFI_SYSTEM_TABLE *SystemTable + ) +{ + Print(L"%d\n", Plus2(3)); + + return EFI_SUCCESS; +} +``` + +UefiLessonsPkg/SimpleLibraryUser/SimpleLibraryUser.inf +``` +[Defines] + INF_VERSION = 1.25 + BASE_NAME = SimpleLibraryUser + FILE_GUID = 22a1f57c-21ca-4011-9133-e3df0d01dace + MODULE_TYPE = UEFI_APPLICATION + VERSION_STRING = 1.0 + ENTRY_POINT = UefiMain + +[Sources] + SimpleLibraryUser.c + +[Packages] + MdePkg/MdePkg.dec + UefiLessonsPkg/UefiLessonsPkg.dec <--- we need to include this for the same reason as in library INF file (for the header search) + +[LibraryClasses] + UefiApplicationEntryPoint + UefiLib + SimpleLibrary <--- library is included as usual +``` + +Now add modifications to the `UefiLessonsPkg/UefiLessonsPkg.dsc`: +``` +[LibraryClasses] + ... + SimpleLibrary|UefiLessonsPkg/Library/SimpleLibrary/SimpleLibrary.inf + +[Components] + ... + UefiLessonsPkg/SimpleLibraryUser/SimpleLibraryUser.inf +``` +Here we've added implementation for our library class and added our new module to the package components. + +If you build everything now and execute it under OVMF, you would get: +``` +FS0:\> SimpleLibraryUser.efi +5 +``` + +`3+2` is indeed `5`, so our library works correctly! + -- cgit v1.2.3-18-g5258