Building A Platform¶

You have an EDK2 implementation, a platform DSC, and a platform FDF? Great! You are one settings file away from a great platform building experience.

The build process has three stuart commands to take your firmware code tree from freshly cloned to fully built: stuart_setup, stuart_update, stuart_build (hereby known has the "command(s)"). Behind the scenes, each command is an Invocable that has a corresponding Settings Manager that the platform subclasses to provide platform specific information.

In hopes of keeping this section as light as possible, the information provided will be broad and more conversational then tutorial. If you want a step by step example of porting a platform, we have one! Please see Porting the Raspberry Pi 3.

Getting Started¶

Stuart needs a settings file to configure itself. This settings file must provide a settings manager subclasses for each command you plan on using. This settings manager is the interface that provides platform specific information to the platform agnostic invocable. This is done via subclassing the corresponding settings file and overriding the necessary methods described in the Settings Manager.

In terms of building a platform, there are five classes that you need to be aware of. The first two are interfaces that provide functions used across all three commands and can be shared among the SettingsManagers by using Multiple Inheritance.

The final class we inherit from in the settings file the UefiBuilder and is what provides the bulk of customization EDK2 Pytools affords you. This is also where you can utilize many of the features and functionality spread across Edk2-Pytools (Extensions and Library).

Lets take a look at each command!

Stuart Setup¶

stuart_setup is the first command and is responsible for setting up the code tree. Currently, this only involves preparing the git submodules necessary for build. If you've created an Omnicache, here is where you would use it to save on network bandwidth, disk space, and time when cloning repos. As you might expect, stuart_setup does not automatically know what submodules are necessary for each platform; we must use the SetupSettingsManager to provide that information.

Note

The command specific Settings Manager may not provide ALL platform data required by the command; it only provides the platform data specific to that command. You still need to override some methods from Edk2InvocableSettingsInterface and MultiPkgAwareSettingsInterface that multiple (or all) commands use, which is why they are in the parent class. Don't worry though! If you miss overriding a required method, you'll raise a NotImplementedError!

Review the stuart_setup specific settings manager here.

Stuart Update¶

Next up is stuart_update, which is responsible for updating any external dependencies in the workspace. This includes downloading and performing miscellaneous tasks for external dependencies. You can find details on how external dependencies work and how to utilize them in the ext_dep section.

As you'll see in the API reference for UpdateSettingsManager, no additional methods need to be overwritten. At first glance, it may seem like stuart_update does not need any platform specific information, but it actually does. The key takeaway is that you'll still need to inherit from UpdateSettingsManager; it's just that the necessary platform data for this command comes from overriding methods in the parent class Edk2InvocableSettingsInterface and/or MultiPkgAwareSettingsInterface.

Review the stuart_update specific settings manager here.

Stuart Build¶

Lastly is the stuart_build command, which actually has two phases to it. The first phase is executed via the stuart_build command and uses the BuildSettingsManager to setup the environment in preparation for the build. It will then invoke the UefiBuilder, signaling the start of the second phase which consists of most of the customization afforded to you by EDK2 Pytools.

Review the stuart_build specific settings manager here.

UefiBuilder¶

So what has all of these commands been culminating to? They've all been working to prepare a Self Describing Environment for the UefiBuilder to operate in. The purpose of the UefiBuilder is to allow the platform to perform various tasks using this environment. Custom made UefiBuildPlugins will automatically be run Pre and Post build for all platforms while UefiHelperPlugins will be available to the developer to help create Platform specific Pre and Post build functionality. The UefiBuilder class has a lot to it, so let's take a look at each part.

Command Line options¶

UefiBuilder has multiple built in command line options that control the flow of the build. The below code snippet shows these command line variables and are accessible via self.<dest>. Developers can use this to help control flow in any of the overrideable methods described in the following sections, however they are also used to control build flow outside the control of the developer.

Adds command line options to the argparser.

Parameters:

Name	Type	Description	Default
`parserObj`	`argparser`	argparser object	required

Source code in edk2toolext/environment/uefi_build.py

def AddPlatformCommandLineOptions(self, parserObj: argparse.ArgumentParser) -> None:
    """Adds command line options to the argparser.

    Args:
        parserObj (argparser): argparser object
    """
    parserObj.add_argument("--SKIPBUILD", "--skipbuild", "--SkipBuild", dest="SKIPBUILD",
                           action='store_true', default=False, help="Skip the build process")
    parserObj.add_argument("--SKIPPREBUILD", "--skipprebuild", "--SkipPrebuild", dest="SKIPPREBUILD",
                           action='store_true', default=False, help="Skip prebuild process")
    parserObj.add_argument("--SKIPPOSTBUILD", "--skippostbuild", "--SkipPostBuild", dest="SKIPPOSTBUILD",
                           action='store_true', default=False, help="Skip postbuild process")
    parserObj.add_argument("--FLASHONLY", "--flashonly", "--FlashOnly", dest="FLASHONLY",
                           action='store_true', default=False, help="Flash rom after build.")
    parserObj.add_argument("--FLASHROM", "--flashrom", "--FlashRom", dest="FLASHROM",
                           action='store_true', default=False, help="Flash rom.  Rom must be built previously.")
    parserObj.add_argument("--UPDATECONF", "--updateconf", "--UpdateConf",
                           dest="UPDATECONF", action='store_true', default=False,
                           help="Update Conf. Builders Conf files will be replaced with latest template files")
    parserObj.add_argument("--CLEAN", "--clean", "--CLEAN", dest="CLEAN",
                           action='store_true', default=False,
                           help="Clean. Remove all old build artifacts and intermediate files")
    parserObj.add_argument("--CLEANONLY", "--cleanonly", "--CleanOnly", dest="CLEANONLY",
                           action='store_true', default=False,
                           help="Clean Only. Do clean operation and don't build just exit.")
    parserObj.add_argument("--OUTPUTCONFIG", "--outputconfig", "--OutputConfig",
                           dest='OutputConfig', required=False, type=str,
                           help='Provide shell variables in a file')

While we don't provide you the ability to override this function (without being hacky like overriding it anyway and calling the superclass in your override), there is an easy way to add CLI options to your build, which is through Platform Environment Variables

Platform Environment Variables¶

Platform environment variables are a powerful tool used throughout the build process. Not only do environment variables allow you to control build flow within the UefiBuilder, but they also are used by the platform fdf and dsc. You can set platform environment variables in the platform DSC, FDF, Settings File, and Command Line; any variable set in one is available in the others! A simple example of this would be to add or remove features based off some criteria. With Edk2-Pytools this is as simple as setting a single env variable during build. We will walk through this example soon.

Setting / Getting Environment Variables¶

It's easy set and get environment variables in the FDF, DSC, Settings file, and Command line as seen in the table below:

Type	Set	Get
Command Line	VAR [= Value]	N/A
FDF/DSC	DEFINE VAR = Value	$(VAR)
Settings File	env.SetValue(Var, Value)	env.GetValue(Var, DefaultValue)

To support parity with Edk2's build command line option -D/--define, variables passed via the command line are not required to have a value associated with them. Variables defined this way are considered non-valued variable defines and should be checked for existence rather then value (i.e. if env.GetValue(var): or if not env.GetValue(var)).

While you can set and get variables anywhere in the UefiBuilder portion of the settings file, we provide the following three methods to set environment variables, ensuring they are available everywhere that you are allowed to customize:

Warning

SetPlatformDefaultEnv is not like the others. Rather then setting the environment variables directly, it should return a limited list of the most commonly overridden variables and their default values! The values returned are printed to the terminal when using the -h, --help flags so that develops can easily find the common ways to customize a platforms build. Additionally, if these variables have not been set anywhere else in the build, they will be set to the default values.

Note

Not all variables are passed through stuart to the actual build command. Only variables with the prefix BLD_*_, BLD_DEBUG_ and BLD_RELEASE_ are considered build values and consumed by the build command.

Example¶

As mentioned above, lets walk through a simple example of build customization with Edk2-Pytools. In this scenario, we want a simple way to build our platform in three distinct ways. To keep it simple, all we want to customize is the target type (DEBUG/RELEASE) and the inclusion of the EdkShell. These builds will be DEV, SELFHOST, and RELEASE. From the command line, we we would call stuart_build -c Platform.py PROFILE=DEV. All that needs to be done is to check the value of profile during SetPlatformEnv() and make our build customizations from there.

def __init__(self):
    self.profiles = {
        "DEV" : {"TARGET" : "DEBUG", "EDK_SHELL": ""},
        "SELFHOST" : {"TARGET" : "RELEASE", "EDK_SHELL": ""},
        "RELEASE" : {"TARGET" : "RELEASE"}
    }
...

def SetPlatformEnv(self):
    build_profile = self.env.GetValue("PROFILE", "DEV") # Default DEV
    if build_profile in self.profiles:
        for key, value in self.profile[build_profile].items():
            self.env.SetValue(key, value, "PROFILE VALUE")
...

The environment variables are set, whats next? The target is automatically picked up by the build system, so all that needs to be done is to add the logic of including the Edk shell or not. This can be done in the platform fdf as seen below:

!if $(EDK_SHELL)
FILE APPLICATION = PCD(gPcBdsPkgTokenSpaceGuid.PcdShellFile) {
  SECTION PE32 = <SomePath>/Shell.efi
  SECTION UI = "EdkShell"
}
!endif

Pre / Post Build Customization¶

Edk2 Pytools offer developers multiple ways to customize the build experience, both Pre and Post Build. The first way is through UefiBuildPlugins (executed automatically for all platforms) which is discussed in Create a Plugin section, and through three methods to override in the UefiBuilder (specific to the platform) which will be the focus here.

All three of the callbacks that you can override have access to the same environment, but each happens at a different time in the build process as outlined below. You can choose to perform specific tasks both prebuild and postbuild such as moving files around pre build or patching in binary data post build. We also offer a callback for flashing your image to the device, if you have the infrastructure to do so via command line. You'll have to fully implement it yourself, but it can greatly speed up the time it takes to get your firmware on your platform.

PlatformPreBuild()
UefiBuildPlugins that implement do_pre_build()
Build()
PlatformPostBuild()
UefiBuildPlugins that implement do_post_build()
PlatformFlashImage()

Lets end this section by mentioning some of the important things (but not everything) you have access to during the callbacks mentioned above:

Helper Plugins¶

This is another type of plugin that is talked about in the Create a Plugin that allows the developers to add in extensions or helper methods to the build environment that are easy to access. You can easily access them through self.Helper.<FunctionName>(). As an example, if we made that helper called YamlToBin(yaml_obj), then we could call it via self.Helper.JsonToBin(yaml).

The Environment¶

As we alluded to in one of the previous sections, you'll have access to all of the environment variables set throughout the DSC, FDF, CLI, and anywhere else in the build. you'll be able to access the environment via self.env. To see the available methods to use, please review the VarDict.

Edk2 Pytool Library¶

The second half of Edk2 Pytools is Edk2 Pytool Library, which provides the building blocks of tools that are relevant to UEFI firmware developers. Some of these tools include file parsers for edk2 specific file types and UEFI defined values and interfaces for usage in python. You can think of Edk2 Pytool Extensions (This) as the simple framework to get your platform building and Edk2 Pytool Library as the building blocks to do more advanced customization of the build.