Step to UEFI (301）先于 Windows 启动的 UEFI APP

#include <Uefi.h>
#include <Library/UefiLib.h>
#include <Library/UefiBootServicesTableLib.h>
#include <Library/DevicePathLib.h>
#include <Library/MemoryAllocationLib.h>
#include <Library/PrintLib.h>
#include <Protocol/LoadedImage.h>
#include <Protocol/SimpleFileSystem.h>
#include <Guid/FileInfo.h>

/**
 * 基本的_getch()函数 - 等待并获取一个字符
 * @return 返回按下的字符，如果是特殊键则返回扩展码
 */
CHAR16 _getch(VOID)
{
    EFI_INPUT_KEY Key;
    EFI_STATUS Status;
    
    // 等待按键事件
    Status = gST->ConIn->ReadKeyStroke(gST->ConIn, &Key);
    
    // 如果没有按键，等待按键事件
    while (Status == EFI_NOT_READY) {
        gBS->WaitForEvent(1, &gST->ConIn->WaitForKey, NULL);
        Status = gST->ConIn->ReadKeyStroke(gST->ConIn, &Key);
    }
    
    if (EFI_ERROR(Status)) {
        return 0;
    }
    
    // 如果是普通字符，直接返回
    if (Key.UnicodeChar != 0) {
        return Key.UnicodeChar;
    }
    
    // 如果是特殊键，返回扫描码
    return (CHAR16)(0x100 + Key.ScanCode);
}

/**
 * 启动指定路径的 EFI 应用程序
 */
EFI_STATUS
StartEfiApplication (
  IN EFI_HANDLE        ParentImageHandle,
  IN CHAR16           *ApplicationPath
  )
{
    EFI_STATUS                      Status;
    EFI_HANDLE                      ChildImageHandle;
    EFI_DEVICE_PATH_PROTOCOL        *DevicePath;
    EFI_LOADED_IMAGE_PROTOCOL       *ParentLoadedImage;
    UINTN                           ExitDataSize;
    CHAR16                          *ExitData;

    Print(L"=== Starting EFI Application: %s ===\n", ApplicationPath);

    // 步骤 1: 获取父镜像的 LoadedImage 协议
    Status = gBS->HandleProtocol(
        ParentImageHandle,
        &gEfiLoadedImageProtocolGuid,
        (VOID**)&ParentLoadedImage
    );
    if (EFI_ERROR(Status)) {
        Print(L"ERROR: Failed to get parent LoadedImage protocol: %r\n", Status);
        return Status;
    }
    Print(L"SUCCESS: Got parent LoadedImage protocol\n");

    // 步骤 2: 构建目标应用的设备路径
    DevicePath = FileDevicePath(ParentLoadedImage->DeviceHandle, ApplicationPath);
    if (DevicePath == NULL) {
        Print(L"ERROR: Failed to create device path for %s\n", ApplicationPath);
        return EFI_OUT_OF_RESOURCES;
    }
    Print(L"SUCCESS: Created device path\n");

    // 步骤 3: 加载目标镜像
    Status = gBS->LoadImage(
        FALSE,                  // BootPolicy - FALSE 表示不是启动策略
        ParentImageHandle,      // ParentImageHandle - 父镜像句柄
        DevicePath,             // DevicePath - 目标文件的设备路径
        NULL,                   // SourceBuffer - NULL 表示从设备路径加载
        0,                      // SourceSize - 0 表示从设备路径加载
        &ChildImageHandle       // ImageHandle - 返回的子镜像句柄
    );

    // 释放设备路径内存
    FreePool(DevicePath);

    if (EFI_ERROR(Status)) {
        Print(L"ERROR: LoadImage failed: %r\n", Status);
        return Status;
    }
    Print(L"SUCCESS: Image loaded successfully, Handle = 0x%lx\n", (UINTN)ChildImageHandle);

    // 等待用户按键
    Print(L"Press any key to exit...\n");
    _getch();
	
    // 步骤 4: 启动镜像
    Print(L"Starting image...\n");
    Status = gBS->StartImage(
        ChildImageHandle,       // ImageHandle - 要启动的镜像句柄
        &ExitDataSize,          // ExitDataSize - 返回退出数据大小
        &ExitData               // ExitData - 返回退出数据
    );

    // 步骤 5: 处理启动结果
    if (EFI_ERROR(Status)) {
        Print(L"ERROR: StartImage failed: %r\n", Status);
        
        // 如果有退出数据，显示它
        if (ExitData != NULL && ExitDataSize > 0) {
            Print(L"Exit Data Size: %d bytes\n", ExitDataSize);
            Print(L"Exit Data: %s\n", ExitData);
            
            // 释放退出数据内存
            gBS->FreePool(ExitData);
        }
    } else {
        Print(L"SUCCESS: Image started and returned: %r\n", Status);
        
        // 处理正常退出的数据
        if (ExitData != NULL && ExitDataSize > 0) {
            Print(L"Application returned data: %s\n", ExitData);
            gBS->FreePool(ExitData);
        }
    }

    // 步骤 6: 卸载镜像（如果需要）
    Print(L"Unloading image...\n");
    gBS->UnloadImage(ChildImageHandle);

    Print(L"=== Application execution completed ===\n\n");
    return Status;
}

/**
 * 检查文件是否存在
 */
EFI_STATUS
CheckFileExists (
  IN EFI_HANDLE     DeviceHandle,
  IN CHAR16        *FilePath
  )
{
    EFI_STATUS                      Status;
    EFI_SIMPLE_FILE_SYSTEM_PROTOCOL *FileSystem;
    EFI_FILE_PROTOCOL               *Root;
    EFI_FILE_PROTOCOL               *File;

    // 获取文件系统协议
    Status = gBS->HandleProtocol(
        DeviceHandle,
        &gEfiSimpleFileSystemProtocolGuid,
        (VOID**)&FileSystem
    );
    if (EFI_ERROR(Status)) {
        return Status;
    }

    // 打开根目录
    Status = FileSystem->OpenVolume(FileSystem, &Root);
    if (EFI_ERROR(Status)) {
        return Status;
    }

    // 尝试打开目标文件
    Status = Root->Open(
        Root,
        &File,
        FilePath,
        EFI_FILE_MODE_READ,
        0
    );

    if (!EFI_ERROR(Status)) {
        Print(L"File exists: %s\n", FilePath);
        File->Close(File);
    } else {
        Print(L"File not found: %s (Status: %r)\n", FilePath, Status);
    }

    Root->Close(Root);
    return Status;
}



/**
 * 主入口函数
 */
EFI_STATUS
EFIAPI
UefiMain (
  IN EFI_HANDLE        ImageHandle,
  IN EFI_SYSTEM_TABLE  *SystemTable
  )
{
    EFI_STATUS                Status;
    EFI_LOADED_IMAGE_PROTOCOL *LoadedImage;

    // 清屏
    gST->ConOut->ClearScreen(gST->ConOut);
    
    Print(L"UEFI StartImage Example Application\n");
    Print(L"====================================\n\n");

    // 获取当前镜像信息
    Status = gBS->HandleProtocol(
        ImageHandle,
        &gEfiLoadedImageProtocolGuid,
        (VOID**)&LoadedImage
    );
    if (EFI_ERROR(Status)) {
        Print(L"Failed to get LoadedImage protocol: %r\n", Status);
        return Status;
    }


    // 示例 : 启动 Windows Boot Manager
    Print(L"Example 1: Starting Windows Boot Manager\n");
    CheckFileExists(LoadedImage->DeviceHandle, L"EFI\\Microsoft\\boot\\bootbk.efi");
    Status = StartEfiApplication(ImageHandle, L"EFI\\Microsoft\\boot\\bootbk.efi");
    Print(L"Windows Boot Manager result: %r\n\n", Status);
    return EFI_SUCCESS;
}

## @file
#   A simple, basic, application showing how the Hello application could be
#   built using the "Standard C Libraries" from StdLib.
#
#  Copyright (c) 2010 - 2011, Intel Corporation. All rights reserved.<BR>
#  This program and the accompanying materials
#  are licensed and made available under the terms and conditions of the BSD License
#  which accompanies this distribution. The full text of the license may be found at
#  http://opensource.org/licenses/bsd-license.
#
#  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
#  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
##

[Defines]
  INF_VERSION                    = 0x00010006
  BASE_NAME                      = bootmgfw
  FILE_GUID                      = 4ea97c46-7491-2025-1125-747010f3ce5f
  MODULE_TYPE                    = UEFI_APPLICATION
  VERSION_STRING                 = 0.1
  ENTRY_POINT                    = UefiMain

#   
#  VALID_ARCHITECTURES           = IA32 X64 IPF
#

[Sources]
  StartImageTest.c

[Packages]
  MdePkg/MdePkg.dec

[LibraryClasses]
  UefiApplicationEntryPoint
  UefiLib
  UefiBootServicesTableLib
  
[Protocols]
  gEfiLoadedImageProtocolGuid
  gEfiSimpleFileSystemProtocolGuid
  gEfiSimpleTextInProtocolGuid
  gEfiSimpleTextOutProtocolGuid

  
[BuildOptions]

[Guids]