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EDK II Code Formatting

To better realize the goals of the EDK II C Coding Standards Specification, EDK II code formatting is automated using a source code beautifier called Uncrustify. Uncrustify is compatible with C/C++ in addition to other languages. In EDK II, it is used to format C language source code.

Uncrustify in the edk2 Repository

The Uncrustify collateral in the edk2 repository contains all of the resources needed to get the Uncrustify application and run it with the same settings as other developers.

Uncrustify is automatically run against code submitted in edk2 as a continuous integration (CI) plugin called "UncrustifyCheck". The plugin is available in the following directory: .pytool/Plugin/UncrustifyCheck

The UncrustifyCheck plugin in edk2 contains the following files used to check code for compliance to the coding standard:

  • default_file_header.txt - A text file containing a template that is placed at the top of files missing a file header.
  • default_function_header.txt - A text file containing a template that is placed above functions that are missing a function header.
  • - A file that contains details about how the plugin works and how to use it.
  • uncrustify_ext_dep.yml - An "external dependency" file that is used to get the current version of the Uncrustify application used by the plugin. This file contains the NuGet feed URL and the version currently used.
  • uncrustify_plug_in.yaml - A file that contains information to describe the plugin to the build environment.
  • uncrustify.cfg - A file used by the Uncrustify application to control how it formats code. If you want to tweak particular formatting details, this is the place to start.
  • - The actual Python file that is the CI plugin. Like all CI plugins, this plugin can be run in local CI and server CI.

How to Find Uncrustify Formatting Errors in Continuous Integration (CI)

The EDK II project uses Azure Pipelines to check that pull requests meet the compilation and formatting requirements for new code submissions. If a code formatting error is found, the UncrustifyCheck plugin will indicate the files that contained errors and, if the option is enabled (it currently is by default), a detailed diff of the formatting changes required for the code to pass the formatting checks.

This section provides the instructions on how to locate these pieces of information in the Azure Pipelines UI. It is based on a PR that intentionally introduces a code formatting issue in MdeModulePkg/Core/Dxe/DxeMain/DxeMain.c.

  1. Recognize the problem in the GitHub PR

    EDK II pull requests are tracked in the "Pull Requests" tab.

    The CI build results are visible in real-time. If any checks fail, the pipeline that contained the failure will be associated with a red "x" (as opposed to a green check mark).


    Failure in Pull Request

    We are going to follow the first pipeline "Ubuntu GCC5 PR" to investigate the problem by clicking "Details".

  2. Determine the Failure Reason

    Reasons for PR Failure

    On this page, it is shown that 1 failure occurred and that is due to 1 incorrectly formatted file in MdeModulePkg.

    To get more information, we need to go to the pipeline. That is done by clicking "View more details on Azure Pipelines".

  3. Find the Failing Job in the Pipeline

    We are now presented with a list of jobs that make up the pipeline. At least one should have failed. In the case shown below, it is "Build_GCC5 TARGET_MDEMODULE_RELEASE".

    Failing Job in Pipeline

    To get more information about this job, click it (Build_GCC5 TARGET_MDEMODULE_RELEASE).

  4. Find the Build Failure Information in the Build Step

    Now a series of steps that make up that build job are shown. At least one should have failed, which led to the job failure. In the case below, it is "Build and Test MdeModulePkg".

    Failing Step in Job

    This confirms the failure occurred from the UncrustifyCheck plugin for one file - MdeModulePkg/Core/Dxe/DxeMain/DxeMain.c.

  5. Go to the Job's Test Results

    At this point, we could go run Uncrustify locally against the file (directions on this page).

    However, we are going to see exactly what changes led to the formatting issue in the file as reported from the CI results.

    Back in the job page, a summary is shown at the top of the page like the following:

    Build Test Results

    To learn more about the test results, click the text. In this case, 92.5% passed.

  6. Go to the Failing Test Results

    We can see the test that failed is the "coding standard compliance" test in MdeModulePkg. We expected that based on the earlier information we found.

    To learn more about this failure, click the test. In this case, Check file coding standard compliance in Edk2CiBuild.Edk2.MdeModulePkg.

    Failing Test Result

  7. Go to the Test Attachments

    We can again see this failure is regarding 1 file in MdeModulePkg. Click Attachments to get the error log which has the detailed information.

    Coding Standard Test Result

  8. Go to the Error Log Attachment

    Now, click the error log to get the error output. In this case, click Standard_Error_Output.log.

    Standard Output Error Log

    This log shows the exact changes that are needed to pass code formatting.

    If the changes are not visible, verify whitespace requirements such as line endings being CRLF are present in the files, especially in newly added files.

EDK II Uncrustify Fork

Due to nuances in the way EDK II formats code, some changes were made to the upstream Uncrustify application. These were changes that could not be controlled purely through the Uncrustify configuration file. For more details about the fork, please visit that project overview in the link below.

Developer Workflow

Developers must install Uncrustify and run the application against their code before sending patch review emails or submitting pull requests. Pull requests run against EDK II CI which includes the UncrustifyCheck CI plugin.

Fortunately, Uncrustify can be installed quickly, you can format your code quickly locally, and you can verify the code against the UncrustifyCheck CI plugin before sending it to others.

The recommended flow is:

  1. Clone the edk2 source code repository
  2. Use the stuart* commands to pull the Uncrustify application into the edk2 workspace
  3. Set up the ability to run Uncrustify locally (for example, using the Visual Studio Code Uncrustify plugin)
  4. Make and test code changes
  5. Format code locally using Uncrustify (for example, using the Visual Studio Code Uncrustify plugin)
  6. Run EDK II CI locally to verify UncrustifyCheck passes
  7. Send the code patch to the EDK II mailing list

Installing Uncrustify

Uncrustify is a portable executable that is built in the EDK II Uncrustify fork repository and ultimately published into a NuGet feed in that fork project.

Recommended Installation: In edk2 repository

It is strongly recommended to follow this flow. It sets up the workspace to work with local CI and automatically gets the current supported version of the application.

The Uncrustify tool is installed automatically when the pytools environment is used and the stuart* commands are run to complete environment setup. Review the edk2 .pytool/ file for details on stuart and this overall flow.

After running the stuart_update command, the Uncrustify application content should be brought down into .pytool\Plugin\UncrustifyCheck\mu-uncrustify-release_extdep in your edk2 workspace. The contents of this directory now represent the contents of the NuGet package and it should contain a Linux and Windows executable of the application.

Manual Installation: Download from the fork project

The release pipeline in the EDK II Uncrustify fork project contains the build information for each release. Each build in this pipeline represents a release. By going to a specific build, the details mapping the build to source code (such as the branch and commit) are present.

The build content is published as a NuGet package to a NuGet feed. This is the same feed, the recommended installation instructions automatically pull from. The NuGet feed is available in the "Artifacts" section of the fork project. If you hover/click on a specific package entry (e.g. "mu-uncrustify-release"), a set of three ellipsis will appear. Click the ellipsis and a context menu will appear. The NuGet package can be downloaded by clicking "Download <x.y.z>".

Once downloaded, the .nupkg file can be treated as a zip file. If the file is opened as a zip file, the executable can be found in the mu-uncrustify-<debug/release> directory.

How to Run Uncrustify

Once Uncrustify is installed, you can run the application in a number of ways. In all cases, you should be using the Uncrustify application built from the Uncrustify EDK II fork and the Uncrustify configuration file currently checked into edk2.

Recommended Usage: Visual Studio (VS) Code Plugin

The Visual Studio Code plugin provides a way to seamlessly run Uncrustify against code at anytime in the editor and the configuration details are set once in the editor configuration file.

  1. Install the Uncrustify VS Code extension:

    Name: Uncrustify Id: zachflower.uncrustify Description: Code format using uncrustify Publisher: Zachary Flower VS Marketplace Link:

  2. Configure the Uncrustify plugin for your local setup by adding the following to your VS Code settings.json file: (Windows example)

    "": "path_to_your_config_file",
    "": "path_to_your_uncrustify_executable"

    Windows Example:

    "": "D:/src/edk2/.pytool/Plugin/UncrustifyCheck/uncrustify.cfg",
    "": "D:/src/edk2/.pytool/Plugin/UncrustifyCheck/mu-uncrustify-release_extdep/Windows-x86/uncrustify.exe"
  3. Open a C source code file, Ctrl+Shift+P -> Format Document With... -> Configure Default Formatter -> Uncrustify

  4. Then, Ctrl+Shift+P -> Format Document any time you would like to format your source code file with Uncrustify

Manual Usage: Run in a Terminal

These instructions are written for Windows 10. These activities could be further automated into a high-level script but that has not been done yet.

Manual Usage - Generate File List

Uncrustify must be given a list of files to run against. This can be done by redirecting the list to stdin or by providing a text file. Examples of how perform both approaches are given below.

Manual Usage - Generate File List via stdin

This is the recommended way to manually run Uncrustify. It is works across Linux and Windows and reduces the number of overall steps.

Example to run against all .c and .h files in DynamicTablesPkg executed from the root of the edk2 workspace.


git ls-files DynamicTablesPkg*.c DynamicTablesPkg*.h | ./.pytool/Plugin/UncrustifyCheck/mu-uncrustify-release_extdep/Linux-x86/uncrustify -c ./.pytool/Plugin/UncrustifyCheck/uncrustify.cfg -F - --replace --no-backup --if-changed


git ls-files DynamicTablesPkg*.c DynamicTablesPkg*.h | .\.pytool\Plugin\UncrustifyCheck\mu-uncrustify-release_extdep\Windows-x86\uncrustify.exe -c .\.pytool\Plugin\UncrustifyCheck\uncrustify.cfg -F - --replace --no-backup --if-changed
  • The git ls-files command is used to gather the list of .c and .h files in DynamicTablesPkg
  • The output from git ls-files is redirected to uncrustify
  • The following options are given to the Uncrustify application:
    • -c: The path to the Uncrustify configuration file
    • -F: Read the files one per line. - indicates the list should be read from stdin.
    • --replace: Replace the source files in place (convenient to diff formatting with git)
    • --no-backup: Replace files with no backup (again, useful to diff formatting with git)
    • --if-changed: Only produce output if a change is detected.
Manual Usage - Generate File List via Text File
  1. Generate a list of the files to run against. This example generates a recursive list of all .c and .h files.

    • It is recommended to run this in cleanly cloned edk2 repo without submodules to prevent submodule files (such as Brotli files in MdeModulePkg) from getting included in the file list (if you are running against all files). Including all files will significantly increase the amount of time Uncrustify takes to run.

    • Sample Powershell command to recursively write all .c and .h files in a given package to a text file (this can of course be done with other languages/commands):

      Get-ChildItem -Path .\MdePkg\* -Include *.c, *.h -Recurse -Force | %{$_.fullname} | Out-File
      -FilePath .\MdePkgFiles.txt -Encoding utf8

    WARNING Powershell will put the UTF-8 BOM at the beginning of the output file. Uncrustify does not recognize the BOM and it should be removed before passing the file as input to Uncrustify. If it is not removed, Uncrustify will not read the first file path in the text file properly which will cause the file to not be formatted. Keep this in mind regardless of the method used for generating the text file.

  2. Run Uncrustify using the generated text file as input

Example to run against all .c and .h files in MdePkg executed from the root of the edk2 workspace.


.\.pytool\Plugin\UncrustifyCheck\mu-uncrustify-release_extdep\Windows-x86\uncrustify.exe -c .\.pytool\Plugin\UncrustifyCheck\uncrustify.cfg -F MdePkgFiles.txt --replace --no-backup --if-changed
  • The following options are given to the Uncrustify application:

    • -c: The path to the Uncrustify configuration file
    • -F: Read the files one per line from the file MdePkgFiles.txt
    • --replace: Replace the source files in place (convenient to diff formatting with git)
    • --no-backup: Replace files with no backup (again, useful to diff formatting with git)
    • --if-changed: Only produce output if a change is detected.

    Note: When testing a configuration change, it is sometimes useful to run Uncrustify against a particular file and check the debug output to understand what rule was applied and why it was applied. The command shows an example of how to run the configuration file uncrustify.cfg against the source file VariableSmm.c where the file is forced to be treated as C, the debug output is written to uncrustify_debug.txt and the log severity level is set to "all".


    .\.pytool\Plugin\UncrustifyCheck\mu-uncrustify-release_extdep\Windows-x86\uncrustify.exe -c .\.pytool\Plugin\UncrustifyCheck\uncrustify.cfg -f .\MdeModulePkg\Universal\Variable\RuntimeDxe\VariableSmm.c -o output.c -l C -p uncrustify_debug.txt -L A 2>verbose_debug.txt

Uncrustify will update the source files in-place (with the commands given). This allows you to diff the results with git. From here, you can iteratively tweak the configuration file and check the results until you are satisfied with the outcome.

Uncrustify in CI

The UncrustifyCheck CI plugin that will verify formatting on the server can be run locally. It is recommended to run local CI to verify the patch submission will pass CI on the server.

This can be done using the stuart_ci_build command.

Tip: To quickly only run UncrustifyCheck, remove the other plugin directories from your local .pytool directory and, of course, add them back when you're done.

Here's an example of running UncrustifyCheck against MdeModulePkg from the root of an edk2 workspace:

stuart_ci_build -c .pytool/ -p MdeModulePkg

If a file has a formatting error, it will be noted in the output from stuart_ci_build. This is visible in the terminal output in local CI and the build output log in server CI.

Read the UncrustifyCheck to understand more about how the plugin can be configured for CI.

Extra Reading: Tracing History Across the Uncrustify Transition in edk

Note: Most users do not need to read this section.

It might be helpful to view the entire history rewritten with Uncrustify formatting on every commit. For example, an alternate version of the edk2 repository that serves as "documentation" with the entire history re-written.

A tool called git-filter-repo can be used to perform this transformation and runs in a reasonable period of time (a few hours):

The following steps can be used to perform this transformation. This is the Windows process. A Linux process will be added in the future.

WARNING This operation modifies (rewrites) all the commits in the local copy of the repo. Do not perform these steps on a local repo you are using for active development.

  1. Clone edk2 into a new directory (see WARNING)

    git clone edk2-uncrustified
    cd edk2-uncrustified
  2. Setup python virtual env, install pytools, and run stuart commands to setup build environment which includes installing uncrustify tools. See Running CI Locally.

  3. Make a backup copy of the plugin UncrustifyCheck outside WORKSPACE. (e.g. C:\Temp\UncrustifyCheck) so the Uncrustify executable and EDK II specific Uncrustify configuration file are available when working with a branch that does not have those tools in its scope.

    xcopy .pytool\Plugin\UncrustifyCheck C:\Temp\UncrustifyCheck
  4. Use from git-filter-repo examples

Line #127 - Add try except around subprocess.check_call() with except being pass. This is required because there are a few commits of C files in the edk2 repo that have incorrect C syntax and do not build with a C compiler and break the Uncrustify parser. Skip reformat of C files that can not be parsed by uncrustify. These rare instances are addressed in the commit that fixes the C syntax error.

Run this slightly modified version of lint-history. Include only .c/.h files and exclude directories that start with Tools or BaseTools. This step took about 2.2 hours on a laptop.
    --relevant "return (not filename.startswith(b'Tools') and not filename.startswith(b'BaseTools') and (filename.endswith(b'.c') or filename.endswith(b'.h')))"
    c:\\work\\GitHub\\tianocore\\foo\\UncrustifyCheck\\mu-uncrustify-release_extdep\\Windows-x86\\uncrustify.exe -c c:\\work\\GitHub\\tianocore\\foo\\UncrustifyCheck\\uncrustify.cfg --replace --no-backup --if-changed