Re: [edk2-devel][Patch 1/3] MdePkg/UefiDebugLibConOut: Add destructor to CloseEvent

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 7/29/19 6:09 PM, Laszlo Ersek wrote:
> On 07/29/19 16:38, Philippe Mathieu-Daudé wrote:
>> Hi,
>>
>> On 7/26/19 5:10 AM, Xu, Wei6 wrote:
>>> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2012
>>>
>>> When driver is unloaded, the ExitBootSerivesEvent must be closed at
>>> the same time. Otherwise exception will occur when ExitBootServices.
>>>
>>> Cc: Michael D Kinney <michael.d.kinney@intel.com>
>>> Cc: Liming Gao <liming.gao@intel.com>
>>> Signed-off-by: Wei6 Xu <wei6.xu@intel.com>
>>> ---
>>>  .../UefiDebugLibConOut/DebugLibConstructor.c       | 23 ++++++++++++++++++++++
>>>  .../UefiDebugLibConOut/UefiDebugLibConOut.inf      |  1 +
>>>  2 files changed, 24 insertions(+)
>>>
>>> diff --git a/MdePkg/Library/UefiDebugLibConOut/DebugLibConstructor.c b/MdePkg/Library/UefiDebugLibConOut/DebugLibConstructor.c
>>> index 8005370372..ed73f92818 100644
>>> --- a/MdePkg/Library/UefiDebugLibConOut/DebugLibConstructor.c
>>> +++ b/MdePkg/Library/UefiDebugLibConOut/DebugLibConstructor.c
>>> @@ -73,5 +73,28 @@ DxeDebugLibConstructor(
>>>                                  &mExitBootServicesEvent
>>>                                  );
>>>  
>>>    return EFI_SUCCESS;
>>>  }
>>> +
>>> +/**
>>> +  The destructor closes Exit Boot Services Event.
>>> +
>>> +  @param  ImageHandle   The firmware allocated handle for the EFI image.
>>> +  @param  SystemTable   A pointer to the EFI System Table.
>>> +
>>> +  @retval EFI_SUCCESS   The destructor always returns EFI_SUCCESS.
>>> +
>>> +**/
>>> +EFI_STATUS
>>> +EFIAPI
>>> +DxeDebugLibDestructor(
>>> +  IN EFI_HANDLE                 ImageHandle,
>>> +  IN EFI_SYSTEM_TABLE           *SystemTable
>>> +  )
>>> +{
>>> +  if (mExitBootServicesEvent != NULL) {
>>> +    SystemTable->BootServices->CloseEvent (mExitBootServicesEvent);
>>> +  }
>>
>> Is it OK to let mDebugST (pointer to SystemTable) initialized?
> 
> Yes, ignoring "mDebugST" in this function should be.
> 
> "mDebugST" is a global variable (= an object with file scope and static
> storage duration) defined in
> "MdePkg/Library/UefiDebugLibConOut/DebugLibConstructor.c".
> 
> The library instance (for which the destructor function is being added)
> is linked into driver and application modules. The destructor function
> is invoked whenever the driver or application is about to be unloaded
> from memory. As part of the unloading, the ExitBootServices()
> notification function -- which was automatically registered via the
> constructor function when the driver or application started up -- must
> be de-registered, otherwise the platform firmware will be left with a
> dangling callback pointer. That's what the CloseEvent() above takes care
> of. But it's OK to ignore "mDebugST" altogether, as the memory that
> "mDebugST" lives inside is about to be reclaimed by the platform
> firmware anyway.
> 
> The library destructor is invoked:
> - when a UEFI application exits (with success or failure), by returning
> from its entry point function, or by calling the Exit() boot service
> 
> - when a UEFI driver exits with failure (hence it will be unloaded
> automatically)
> 
> - when a UEFI driver exited with success (hence staying resident), and
> it supports unloading, and now another agent is unloading it with the
> UnloadImage() boot service (such as the UEFI shell with the "unload"
> command, IIRC).

Thanks Laszlo for the explanations!

I noticed (late) this series is already pushed (commits
e92bdcb3ecbf..28bc6992400) so it doesn't require review anymore.

BTW Liming the author name seems incorrect: Wei6 Xu and Xu, Wei6.

>>> +
>>> +  return EFI_SUCCESS;
>>> +}
>>> diff --git a/MdePkg/Library/UefiDebugLibConOut/UefiDebugLibConOut.inf b/MdePkg/Library/UefiDebugLibConOut/UefiDebugLibConOut.inf
>>> index 4c279a5bf2..b577d52ac6 100644
>>> --- a/MdePkg/Library/UefiDebugLibConOut/UefiDebugLibConOut.inf
>>> +++ b/MdePkg/Library/UefiDebugLibConOut/UefiDebugLibConOut.inf
>>> @@ -20,10 +20,11 @@
>>>    MODULE_TYPE                    = UEFI_DRIVER
>>>    VERSION_STRING                 = 1.0
>>>    LIBRARY_CLASS                  = DebugLib|DXE_CORE DXE_DRIVER DXE_RUNTIME_DRIVER UEFI_APPLICATION UEFI_DRIVER
>>>  
>>>    CONSTRUCTOR                    = DxeDebugLibConstructor
>>> +  DESTRUCTOR                     = DxeDebugLibDestructor
>>>  
>>>  #
>>>  #  VALID_ARCHITECTURES           = IA32 X64 EBC
>>>  #
>>>  
>>>
>>
>> 
>>
>