Re: [edk2-devel] [edk2-rfc] MdeModulePkg/StatusCodeHandler: Separate NULL class libraries for Memory and serial handlers from MdeModulePkg/Universal/StatusCodeHandler modules

Brian J. Johnson

Thanks for the link.  I agree that this change will make the StatusCodeHandler driver more modular, and is a step in the right direction.

But I think it could go further, with almost no additional work, and simplify the overall Status Code mechanism, not just the StatusCodeHandler driver.  Currently, the StatusCodeHandler driver entry routines run some initialization code, register callbacks (eg. for ExitBootServices and SetVirtualAddressMap), and call the RscHandler PPI/Protocol to register the worker routines.  If I'm understanding the proposal correctly, all that code will be moved to the individual NULL libraries, since any particular library may or may not need any of it.  Then the StatusCodeHandler modules will be left with no code of their own at all:  they will only be wrappers for the NULL libraries. Their entry routines will do nothing except return EFI_SUCCESS! (1)

It seems strange and wasteful to keep around empty modules like this.  So I'm suggesting adding the NULL libraries to the StatusCodeRouter modules instead.  They would need to export the protocol/PPI routines to the NULL libraries via a header file, so they could call them directly instead of looking up the protocol/PPI.  But that's a minor change.  Then you could remove the empty StatusCodeHandler modules entirely.  The advantage would be that there would be fewer modules in the build, simplifying the .dsc and .fdf files slightly.  It would also reduce code size a bit by sharing common library routines, such as BaseLib, with the StatusCodeRouter modules.

If those don't seem like worthwhile advantages, that's OK with me.  I don't want to belabor the point, or impede progress.  If others are OK with the proposal as it stands, then I am too.


*Brian J. Johnson
*Enterprise X86 Lab

Hewlett Packard Enterprise

(1) The StatusCodeHandlerRuntimeDxe driver also handles PcdStatusCodeReplayIn as part of its entry code.  That code would probably have to stay in a separate module rather than being linked to StatusCodeRouter as a NULL library.  That way it could be dispatched after the ReportStatusCode protocol is available.

*From:* Dong, Eric [mailto:eric.dong@...]
*Sent:* Thursday, June 25, 2020, 10:41 AM
*To:* Brian J. Johnson <brian.johnson@...>, Bi, Dandan <>, Andrew Fish <afish@...>, edk2-devel-groups-io <>
*Cc:* <>, Ni, Ray <>, Wang, Jian J <>, Wu, Hao A <hao.a.wu@...>, Tan, Ming <ming.tan@...>, Laszlo Ersek <lersek@...>
*Subject:* [edk2-devel] [edk2-rfc] MdeModulePkg/StatusCodeHandler: Separate NULL class libraries for Memory and serial handlers from MdeModulePkg/Universal/StatusCodeHandler modules

Hi Brian,

In this new design, we still use register status code handler Protocol/Ppi to register the handler logic. We just want to change the StatusCodeHandler driver. We try to split the register logic to NULL library to make the code more modularity. We already created sample library in Edk2-Platforms repo You can check this code to understand more about what we want to do.



*From:* Brian J. Johnson <brian.johnson@...>
*Sent:* Thursday, June 25, 2020 4:25 AM
*To:* Bi, Dandan <>; Andrew Fish <afish@...>; edk2-devel-groups-io <>
*Cc:*; Dong, Eric <eric.dong@...>; Ni, Ray <>; Wang, Jian J <>; Wu, Hao A <hao.a.wu@...>; Tan, Ming <ming.tan@...>; Laszlo Ersek <lersek@...>
*Subject:* Re: [edk2-devel] [edk2-rfc] MdeModulePkg/StatusCodeHandler: Separate NULL class libraries for Memory and serial handlers from MdeModulePkg/Universal/StatusCodeHandler modules


The Status Code Protocol/PPI is the high-level interface which is being implemented.  The ReportStatusCodeRouter module implements this in terms of the ReportStatusCodeHandler Protocol/PPI.  That allows multiple ReportStatusCodeHandler modules to be used at once, so they can each react to different types of status codes, or report them through multiple channels.  That sort of multiplexing seems like a useful feature.

Now we're considering adding a mechanism which allows registering status code handlers via NULL libraries, rather than via the protocol/PPI. That sounds like exactly what ReportStatusCodeRouter is intended for.  It wouldn't really change its scope, it would just make it more flexible.  Adding this feature via a StatusCodeHandler module wouldn't improve modularity, it would just add complexity.  As an OEM, adding a custom handler would look the same to me either way:  I would have to add the NULL class library to a MdeModulePkg driver's entry in my .dsc file.  It doesn't matter to me whether it's the ReportStatusCodeRouter or StatusCodeHandler module.  And if I can do it in ReportStatusCodeRouter, then I don't need to include any StatusCodeHandler modules in the build at all.  That saves code space and reduces the number of modules in the APRIORI list, which are both good things.

ReportStatusCodeRouterPei already has to track registered handlers in PEI when running from ROM (it uses a HOB.)  Tracking handlers from NULL libraries wouldn't be any harder.  In fact, it looks like it could just export the Register() function to the NULL libraries, and they could call it in their constructors.

I think using NULL libraries for status code handlers is a great idea.  I'd just like to take that opportunity to reduce the complexity of the overall status code stack while we're at it.


*Brian J. Johnson
*Enterprise X86 Lab

Hewlett Packard Enterprise


*From:* Bi, Dandan []

*Sent:* Monday, June 22, 2020, 2:27 AM

*To:* Andrew Fish <afish@...> <mailto:afish@...>, edk2-devel-groups-io <> <>, brian.johnson@... <mailto:brian.johnson@...> <brian.johnson@...> <mailto:brian.johnson@...>

*Cc:* <> <> <>, Dong, Eric <eric.dong@...> <mailto:eric.dong@...>, Ni, Ray <> <>, Wang, Jian J <> <>, Wu, Hao A <hao.a.wu@...> <mailto:hao.a.wu@...>, Tan, Ming <ming.tan@...> <mailto:ming.tan@...>, Laszlo Ersek <lersek@...> <mailto:lersek@...>, Bi, Dandan <> <>

*Subject:* [edk2-devel] [edk2-rfc] MdeModulePkg/StatusCodeHandler: Separate NULL class libraries for Memory and serial handlers from MdeModulePkg/Universal/StatusCodeHandler modules

Hi Brian,

Personally, I prefer to add the NULL class Library to
StatusCodeHandler modules.

1. I think we should make the functionality of each module clear
and separated. It may also be why we added
ReportStatusCodeRouter and StatusCodeHandler modules in edk2
repo before.

ReportStatusCodeRouter modules are responsible for producing
Status Code Protocol/PPI and Report Status Code Handler
Protocol/PPI, and StatusCodeHandler modules are responsible for
producing handlers (Handlers can be provided by NULL class
Libraries in this RFC).

 So, that’s why I don’t want to add the NULL class Library to
ReportStatusCodeRouter modules directly, which change the
functionality scope of existing modules.

2. I agree that we have a lot of layers of indirection now, but
what we may gain is the good modularity. And you also
mentioned that one or more StatusCodeHandler Modules may be
used. We also want to achieve that only the StatusCodeHandler
modules in MdeModulePkg can be used after this separation,
platform can only add its own handler Libs to meet its

3. As Andrew mentioned below, if add the libraries to
ReportStatusCodeRouter, there will be some issue we need to
fix, which seems also make the code logic a little tricky to me.



*From:* Andrew Fish <afish@...> <mailto:afish@...>
*Sent:* Saturday, June 20, 2020 2:04 AM
*To:* edk2-devel-groups-io <>
<>; brian.johnson@...
*Cc:* Bi, Dandan <>
<>; Dong, Eric <eric.dong@...>
<mailto:eric.dong@...>; Ni, Ray <>
<>; Wang, Jian J <>
<>; Wu, Hao A <hao.a.wu@...>
<mailto:hao.a.wu@...>; Tan, Ming <ming.tan@...>
*Subject:* Re: [edk2-devel] [edk2-rfc]
MdeModulePkg/StatusCodeHandler: Separate NULL class libraries for
Memory and serial handlers from
MdeModulePkg/Universal/StatusCodeHandler modules

On Jun 19, 2020, at 10:29 AM, Brian J. Johnson
<brian.johnson@... <mailto:brian.johnson@...>wrote:

On 6/18/20 2:01 AM, Dandan Bi wrote:

Hi All,


We plan to separate two kinds of NULL class libraries for
Memory and serial handlers

The benefit we want to gain from this separation is to 1)
make the code clear and easy to maintain, 2) make platform
flexible to choose any handler library they need, and it
also can reduce image size since the unused handlers can
be excluded.

If you have any concern or comments for this separation,
please let me know.

We plan to add new separated NULL class
different phase implementation

The main tree structure may like below:



|------|------ PeiMemoryStausCodeHandlerLib.inf

|------|------ RuntimeDxeMemoryStatusCodeHandlerLib.inf

|------|------ SmmMemoryStausCodeHandlerLib.inf


|------|------ PeiSerialStatusCodeHandlerLib.inf

|------|------ RuntimeDxeSerialStatusCodeHandlerLib.inf

|------|------ SmmSerialStatusCodeHandlerLib.inf



We will update existing platform use cases in edk2 and
edk2-platform repo to cover the new NULL class library to
make sure this change doesn’t impact any platform.

After this separation, StatusCodeHandler module usage will
like below, and it’s also very flexible for platform to
cover more handler libraries to meet their requirements.



















We'll have a lot of layers of indirection....  The
ReportStatusCodeRouter modules will call one or more
StatusCodeHandlerModules, and the standard StatusCodeHandler
modules will call multiple StatusCodeHandlerLib libraries.

How about adding StatusCodeHandlerLib support directly to the
ReportStatusCodeRouter modules? Then platforms could omit the
StatusCodeHandler modules if they're only using the
open-source code.  That sounds like less overhead since fewer
modules would be needed.

I think the need to execute from ROM makes this tricky.

It looks to me that it is easy to move from PCD to libs for the
StatusCodeHandler since registration is basically
`RscHandlerPpi->Register (SerialStatusCodeReportWorker);`. The
issue I see is the ReportStatusCodeRouter publishes RscHandlerPpi
after the PEIMs constructor has been called and if the PEIM. Given
globals don’t work when running from ROM you would have to do
something like publish a HOB in the library constructor and then
have the GenericStatusCodePeiEntry() walk the HOBs and install the
handlers. So I guess it is a little easier than I 1st thought when
I started writing this mail, but it would require a new public API.


Andrew Fish



*Brian J. Johnson
*Enterprise X86 Lab

Hewlett Packard Enterprise

** <x-msg://64/>


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