Re: [PATCH v3 08/15] MdeModulePkg: Fix constructor invocation ordering

["Ard Biesheuvel" <ard.biesheuvel@arm.com>]

On 6/24/20 3:34 PM, Sami Mujawar wrote:
> The BaseSerialPortLib16550 library does not implement
> a constructor. This prevents the correct constructor
> invocation order for dependent libraries.
> e.g. A PlatformHookLib (for the Serial Port) may have
> a dependency on retrieving data from a Hob. A Hob
> library implementation may configure its initial state
> in the HobLib constructor. Since BaseSerialPortLib16550
> does not implement a constructor, the Basetools do not
> resolve the correct order for constructor invocation.
> 
> To fix this, add an empty constructor to the serial port
> library BaseSerialPortLib16550.
> 
> Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>

Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>

Note to maintainers:
this works around a long standing BaseTools bug where constructor 
dependencies do not propagate through a library that lacks a constructor.

For instance, in the following case

   LibA depends on LibB depends on LibC

the constructors are *only* guaranteed to be invoked in the correct 
order (LibC, then LibB, then LibA) if LibB has a constructor in the 
first place, otherwise, the remaining constructors for LibA and LibC 
could be emitted in any order.



> ---
>   MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550.c   | 17 +++++++++++++++++
>   MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550.inf |  3 +++
>   2 files changed, 20 insertions(+)
> 
> diff --git a/MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550.c b/MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550.c
> index 9cb50dd80d5634ab2aa6d68bf5ca7fb891463eef..0fd1382ee83c9de09d8250830bd9569056fcee2f 100644
> --- a/MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550.c
> +++ b/MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550.c
> @@ -4,6 +4,7 @@
>     (C) Copyright 2014 Hewlett-Packard Development Company, L.P.<BR>
>     Copyright (c) 2006 - 2019, Intel Corporation. All rights reserved.<BR>
>     Copyright (c) 2018, AMD Incorporated. All rights reserved.<BR>
> +  Copyright (c) 2020, ARM Limited. All rights reserved.
>   
>     SPDX-License-Identifier: BSD-2-Clause-Patent
>   
> @@ -1102,3 +1103,19 @@ SerialPortSetAttributes (
>     return RETURN_SUCCESS;
>   }
>   
> +/** Base Serial Port 16550 Library Constructor
> +
> +  @retval RETURN_SUCCESS  Success.
> +*/
> +EFI_STATUS
> +EFIAPI
> +BaseSerialPortLib16550 (
> +  VOID
> +  )
> +{
> +  // Nothing to do here. This constructor is added to
> +  // enable the chain of constructor invocation for
> +  // dependent libraries.
> +  return RETURN_SUCCESS;
> +}
> +
> diff --git a/MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550.inf b/MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550.inf
> index 8b4ae3f1d4ee1e2e9a8b81eab4c900541ce8cfb6..92b7a8b7896a305d2ce22589f8a9593618d37bb7 100644
> --- a/MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550.inf
> +++ b/MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550.inf
> @@ -2,6 +2,8 @@
>   #  SerialPortLib instance for 16550 UART.
>   #
>   #  Copyright (c) 2006 - 2019, Intel Corporation. All rights reserved.<BR>
> +#  Copyright (c) 2020, ARM Limited. All rights reserved.
> +#
>   #  SPDX-License-Identifier: BSD-2-Clause-Patent
>   #
>   ##
> @@ -14,6 +16,7 @@ [Defines]
>     MODULE_TYPE                    = BASE
>     VERSION_STRING                 = 1.1
>     LIBRARY_CLASS                  = SerialPortLib
> +  CONSTRUCTOR                    = BaseSerialPortLib16550
>   
>   [Packages]
>     MdePkg/MdePkg.dec
>