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

["Laszlo Ersek" <lersek@redhat.com>]

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

> 
>> +
>> +  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
>>  #
>>
>>
> 
> 
>