Step to UEFI (98）Shell加载EFI的分析

继续阅读《UEFI 原理与编程》，其中的第三章介绍了一个 EFI Application如何在 Shell下加载运行的。ShellProtocol.c中的InternalShellExecuteDevicePath 是具体实现这个功能的函数。
函数头：

/**
  internal worker function to load and run an image via device path.

  @param ParentImageHandle      A handle of the image that is executing the specified
                                command line.
  @param DevicePath             device path of the file to execute
  @param CommandLine            Points to the NULL-terminated UCS-2 encoded string
                                containing the command line. If NULL then the command-
                                line will be empty.
  @param Environment            Points to a NULL-terminated array of environment
                                variables with the format 'x=y', where x is the
                                environment variable name and y is the value. If this
                                is NULL, then the current shell environment is used.
                            
  @param[out] StartImageStatus  Returned status from gBS->StartImage.

  @retval EFI_SUCCESS       The command executed successfully. The  status code
                            returned by the command is pointed to by StatusCode.
  @retval EFI_INVALID_PARAMETER The parameters are invalid.
  @retval EFI_OUT_OF_RESOURCES Out of resources.
  @retval EFI_UNSUPPORTED   Nested shell invocations are not allowed.
**/
EFI_STATUS
EFIAPI
InternalShellExecuteDevicePath(
  IN CONST EFI_HANDLE               *ParentImageHandle,
  IN CONST EFI_DEVICE_PATH_PROTOCOL *DevicePath,
  IN CONST CHAR16                   *CommandLine OPTIONAL,
  IN CONST CHAR16                   **Environment OPTIONAL,
  OUT EFI_STATUS                    *StartImageStatus OPTIONAL
  )

第一步，先将 EFI Application加载到内存中，生成Image对象。取得这个对象的句柄为 NewHandle。

  //
  // Load the image with:
  // FALSE - not from boot manager and NULL, 0 being not already in memory
  //
  Status = gBS->LoadImage(
    FALSE,
    *ParentImageHandle,
    (EFI_DEVICE_PATH_PROTOCOL*)DevicePath,
    NULL,
    0,
    &NewHandle);

  if (EFI_ERROR(Status)) {
    if (NewHandle != NULL) {
      gBS->UnloadImage(NewHandle);
    }
    return (Status);
  }

第二步，取得命令行参数，将命令行的参数交给 NewHandle

 Status = gBS->OpenProtocol(
    NewHandle,
    &gEfiLoadedImageProtocolGuid,
    (VOID**)&LoadedImage,
    gImageHandle,
    NULL,
    EFI_OPEN_PROTOCOL_GET_PROTOCOL);

  if (!EFI_ERROR(Status)) {
    ASSERT(LoadedImage->LoadOptionsSize == 0);
    if (NewCmdLine != NULL) {
      LoadedImage->LoadOptionsSize  = (UINT32)StrSize(NewCmdLine);
      LoadedImage->LoadOptions      = (VOID*)NewCmdLine;
    }

看到这里我有一个问题：前面加载之后，为什么第二步就能够在被加载的Image上找到“EFI_Loaded_Image_Protocol”? 带着这样的问题追踪了代码。首先要找到 gBS->LoadImage 的真正实现代码，在\MdeModulePkg\Core\Dxe\DxeMain\DxeMain.c有定义，

//
// DXE Core Module Variables
//
EFI_BOOT_SERVICES mBootServices = {
  {
.................
.................
  (EFI_IMAGE_LOAD)                              CoreLoadImage,                            // LoadImage
.................
.................
}

再追CoreLoadImage代码在 \MdeModulePkg\Core\Dxe\Image\Image.c

/**
  Loads an EFI image into memory and returns a handle to the image.

  @param  BootPolicy              If TRUE, indicates that the request originates
                                  from the boot manager, and that the boot
                                  manager is attempting to load FilePath as a
                                  boot selection.
  @param  ParentImageHandle       The caller's image handle.
  @param  FilePath                The specific file path from which the image is
                                  loaded.
  @param  SourceBuffer            If not NULL, a pointer to the memory location
                                  containing a copy of the image to be loaded.
  @param  SourceSize              The size in bytes of SourceBuffer.
  @param  ImageHandle             Pointer to the returned image handle that is
                                  created when the image is successfully loaded.

  @retval EFI_SUCCESS             The image was loaded into memory.
  @retval EFI_NOT_FOUND           The FilePath was not found.
  @retval EFI_INVALID_PARAMETER   One of the parameters has an invalid value.
  @retval EFI_UNSUPPORTED         The image type is not supported, or the device
                                  path cannot be parsed to locate the proper
                                  protocol for loading the file.
  @retval EFI_OUT_OF_RESOURCES    Image was not loaded due to insufficient
                                  resources.
  @retval EFI_LOAD_ERROR          Image was not loaded because the image format was corrupt or not
                                  understood.
  @retval EFI_DEVICE_ERROR        Image was not loaded because the device returned a read error.
  @retval EFI_ACCESS_DENIED       Image was not loaded because the platform policy prohibits the 
                                  image from being loaded. NULL is returned in *ImageHandle.
  @retval EFI_SECURITY_VIOLATION  Image was loaded and an ImageHandle was created with a 
                                  valid EFI_LOADED_IMAGE_PROTOCOL. However, the current 
                                  platform policy specifies that the image should not be started.

**/
EFI_STATUS
EFIAPI
CoreLoadImage (
  IN BOOLEAN                    BootPolicy,
  IN EFI_HANDLE                 ParentImageHandle,
  IN EFI_DEVICE_PATH_PROTOCOL   *FilePath,
  IN VOID                       *SourceBuffer   OPTIONAL,
  IN UINTN                      SourceSize,
  OUT EFI_HANDLE                *ImageHandle
  )
{
  EFI_STATUS    Status;
  UINT64        Tick;
  EFI_HANDLE    Handle;

  Tick = 0;
  PERF_CODE (
    Tick = GetPerformanceCounter ();
  );

  Status = CoreLoadImageCommon (
             BootPolicy,
             ParentImageHandle,
             FilePath,
             SourceBuffer,
             SourceSize,
             (EFI_PHYSICAL_ADDRESS) (UINTN) NULL,
             NULL,
             ImageHandle,
             NULL,
             EFI_LOAD_PE_IMAGE_ATTRIBUTE_RUNTIME_REGISTRATION | EFI_LOAD_PE_IMAGE_ATTRIBUTE_DEBUG_IMAGE_INFO_TABLE_REGISTRATION
             );

  Handle = NULL; 
  if (!EFI_ERROR (Status)) {
    //
    // ImageHandle will be valid only Status is success. 
    //
    Handle = *ImageHandle;
  }

  PERF_START (Handle, "LoadImage:", NULL, Tick);
  PERF_END (Handle, "LoadImage:", NULL, 0);

  return Status;
}
在CoreLoadImageCommon 中可以找到加载安装EFI_Loaded_Image_Protocol 的代码。
  //
  //Reinstall loaded image protocol to fire any notifications
  //
  Status = CoreReinstallProtocolInterface (
             Image->Handle,
             &gEfiLoadedImageProtocolGuid,
             &Image->Info,
             &Image->Info
             );
  if (EFI_ERROR (Status)) {
    goto Done;
  }

就是说，在加载过程中，还要对Image 安装EFI_Loaded_Image_Protocol。因此，Load 的动作并不是简单的读取到内存中。

继续回到InternalShellExecuteDevicePath 代码中。

    //第三步，将修改好的ShellParamsProtocol 再安装到 Image上。
    //
    // Initialize and install a shell parameters protocol on the image.
    //
    ShellParamsProtocol.StdIn   = ShellInfoObject.NewShellParametersProtocol->StdIn;
    ShellParamsProtocol.StdOut  = ShellInfoObject.NewShellParametersProtocol->StdOut;
    ShellParamsProtocol.StdErr  = ShellInfoObject.NewShellParametersProtocol->StdErr;
    Status = UpdateArgcArgv(&ShellParamsProtocol, NewCmdLine, NULL, NULL);
    ASSERT_EFI_ERROR(Status);
    //
    // Replace Argv[0] with the full path of the binary we're executing:
    // If the command line was "foo", the binary might be called "foo.efi".
    // "The first entry in [Argv] is always the full file path of the
    //  executable" - UEFI Shell Spec section 2.3
    //
    ImagePath = EfiShellGetFilePathFromDevicePath (DevicePath);
    // The image we're executing isn't necessarily in a filesystem - it might
    // be memory mapped. In this case EfiShellGetFilePathFromDevicePath will
    // return NULL, and we'll leave Argv[0] as UpdateArgcArgv set it.
    if (ImagePath != NULL) {
      if (ShellParamsProtocol.Argv == NULL) {
        // Command line was empty or null.
        // (UpdateArgcArgv sets Argv to NULL when CommandLine is "" or NULL)
        ShellParamsProtocol.Argv = AllocatePool (sizeof (CHAR16 *));
        if (ShellParamsProtocol.Argv == NULL) {
          Status = EFI_OUT_OF_RESOURCES;
          goto UnloadImage;
        }
        ShellParamsProtocol.Argc = 1;
      } else {
        // Free the string UpdateArgcArgv put in Argv[0];
        FreePool (ShellParamsProtocol.Argv[0]);
      }
      ShellParamsProtocol.Argv[0] = ImagePath;
    }

    Status = gBS->InstallProtocolInterface(&NewHandle, &gEfiShellParametersProtocolGuid, EFI_NATIVE_INTERFACE, &ShellParamsProtocol);
    ASSERT_EFI_ERROR(Status);
//第四步，用 gBS->StartImage执行Image。
    //
    // now start the image and if the caller wanted the return code pass it to them...
    //
    if (!EFI_ERROR(Status)) {
      StartStatus      = gBS->StartImage(
                          NewHandle,
                          0,
                          NULL
                          );
      if (StartImageStatus != NULL) {
        *StartImageStatus = StartStatus;
      }