使用ExitBootServices的简单示例(使用gnu-efi)

#include <Uefi.h>
#include <Protocol/DevicePath.h>
#include <Protocol/GraphicsOutput.h>
#include <Protocol/SimpleTextOut.h>
#include <Protocol/LoadedImage.h>
#include <Library/BaseLib.h>
#include <Library/BaseMemoryLib.h>
#include <Library/MemoryAllocationLib.h>
#include <Library/UefiLib.h>
#include <Library/DebugLib.h>
#include <Library/PrintLib.h>

EFI_STATUS EFIAPI UefiMain(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable)
{
    EFI_STATUS Status;
    EFI_GRAPHICS_OUTPUT_PROTOCOL *GraphicsOutput;
    UINTN Width, Height;
    EFI_GRAPHICS_OUTPUT_MODE_INFORMATION *Info;

    // 初始化 UEFI 环境
    InitializeLib(ImageHandle, SystemTable);

    // 获取 GraphicsOutput 协议
    Status = SystemTable->BootServices->LocateProtocol(
        &gEfiGraphicsOutputProtocolGuid,
        NULL,
        (VOID **)&GraphicsOutput
    );
    if (EFI_ERROR(Status)) {
        return Status;
    }

    // 获取当前图形模式信息
    GraphicsOutput->GetMode(GraphicsOutput->Mode->Mode, &Width, &Height, &Info);

    // 打印一些信息到屏幕
    Print(L"UEFI Firmware - Width: %d, Height: %d\n", Width, Height);

    // 调用 ExitBootServices 切换到操作系统环境
    Status = SystemTable->BootServices->ExitBootServices(ImageHandle, NULL);
    if (EFI_ERROR(Status)) {
        return Status;
    }

    // 从这里开始，UEFI 环境已经切换到操作系统环境
    // 但是通常这里不会执行任何代码，因为操作系统会接管控制权

    return EFI_SUCCESS;
}