Checking out and Building Chromium for Windows

There are instructions for other platforms linked from the get the code page.

Instructions for Google Employees

Are you a Google employee? See go/building-chrome-win instead.

System requirements

  • A 64-bit Intel machine with at least 8GB of RAM. More than 16GB is highly recommended.
  • At least 100GB of free disk space on an NTFS-formatted hard drive. FAT32 will not work, as some of the Git packfiles are larger than 4GB.
  • An appropriate version of Visual Studio, as described below.
  • Windows 7 or newer.

Setting up Windows

Visual Studio

As of September, 2017 (R503915) Chromium requires Visual Studio 2017 update 3.x to build. The clang-cl compiler is used but Visual Studio's header files, libraries, and some tools are required. Visual Studio Community Edition should work if its license is appropriate for you. You must install the “Desktop development with C++” component and the “MFC and ATL support” sub-component. This can be done from the command line by passing these arguments to the Visual Studio installer that you download:

--add Microsoft.VisualStudio.Workload.NativeDesktop
    --add Microsoft.VisualStudio.Component.VC.ATLMFC --includeRecommended

You must have the version 10.0.15063 Windows 10 SDK installed. This can be installed separately or by checking the appropriate box in the Visual Studio Installer.

The SDK Debugging Tools must also be installed. If the Windows 10 SDK was installed via the Visual Studio installer, then they can be installed by going to: Control Panel → Programs → Programs and Features → Select the “Windows Software Development Kit” → Change → Change → Check “Debugging Tools For Windows” → Change. Or, you can download the standalone SDK installer and use it to install the Debugging Tools.

Install depot_tools

Download the depot_tools bundle and extract it somewhere.

Warning: DO NOT use drag-n-drop or copy-n-paste extract from Explorer, this will not extract the hidden “.git” folder which is necessary for depot_tools to autoupdate itself. You can use “Extract all…” from the context menu though.

Add depot_tools to the start of your PATH (must be ahead of any installs of Python). Assuming you unzipped the bundle to C:\src\depot_tools, open:

Control Panel → System and Security → System → Advanced system settings

If you have Administrator access, Modify the PATH system variable and put C:\src\depot_tools at the front (or at least in front of any directory that might already have a copy of Python or Git).

If you don't have Administrator access, you can add a user-level PATH environment variable and put C:\src\depot_tools at the front, but if your system PATH has a Python in it, you will be out of luck.

Also, add a DEPOT_TOOLS_WIN_TOOLCHAIN system variable in the same way, and set it to 0. This tells depot_tools to use your locally installed version of Visual Studio (by default, depot_tools will try to use a google-internal version).

From a cmd.exe shell, run the command gclient (without arguments). On first run, gclient will install all the Windows-specific bits needed to work with the code, including msysgit and python.

  • If you run gclient from a non-cmd shell (e.g., cygwin, PowerShell), it may appear to run properly, but msysgit, python, and other tools may not get installed correctly.
  • If you see strange errors with the file system on the first run of gclient, you may want to disable Windows Indexing.

After running gclient open a command prompt and type where python and confirm that the depot_tools python.bat comes ahead of any copies of python.exe. Failing to ensure this can lead to overbuilding when using gn - see

Get the code

First, configure Git:

$ git config --global "My Name"
$ git config --global ""
$ git config --global core.autocrlf false
$ git config --global core.filemode false
$ git config --global branch.autosetuprebase always

Create a chromium directory for the checkout and change to it (you can call this whatever you like and put it wherever you like, as long as the full path has no spaces):

$ mkdir chromium && cd chromium

Run the fetch tool from depot_tools to check out the code and its dependencies.

$ fetch chromium

If you don't want the full repo history, you can save a lot of time by adding the --no-history flag to fetch.

Expect the command to take 30 minutes on even a fast connection, and many hours on slower ones.

When fetch completes, it will have created a hidden .gclient file and a directory called src in the working directory. The remaining instructions assume you have switched to the src directory:

$ cd src

Optional: You can also install API keys if you want your build to talk to some Google services, but this is not necessary for most development and testing purposes.

Setting up the build

Chromium uses Ninja as its main build tool along with a tool called GN to generate .ninja files. You can create any number of build directories with different configurations. To create a build directory:

$ gn gen out/Default
  • You only have to run this once for each new build directory, Ninja will update the build files as needed.
  • You can replace Default with another name, but it should be a subdirectory of out.
  • For other build arguments, including release settings, see GN build configuration. The default will be a debug component build matching the current host operating system and CPU.
  • For more info on GN, run gn help on the command line or read the quick start guide.

Using the Visual Studio IDE

If you want to use the Visual Studio IDE, use the --ide command line argument to gn gen when you generate your output directory (as described on the get the code page):

$ gn gen --ide=vs out\Default
$ devenv out\Default\all.sln

GN will produce a file all.sln in your build directory. It will internally use Ninja to compile while still allowing most IDE functions to work (there is no native Visual Studio compilation mode). If you manually run “gen” again you will need to resupply this argument, but normally GN will keep the build and IDE files up to date automatically when you build.

The generated solution will contain several thousand projects and will be very slow to load. Use the --filters argument to restrict generating project files for only the code you're interested in, although this will also limit what files appear in the project explorer. A minimal solution that will let you compile and run Chrome in the IDE but will not show any source files is:

$ gn gen --ide=vs --filters=//chrome out\Default

There are other options for controlling how the solution is generated, run gn help gen for the current documentation.

Faster builds

  • Reduce file system overhead by excluding build directories from antivirus and indexing software.
  • Store the build tree on a fast disk (preferably SSD).
  • The more cores the better (20+ is not excessive) and lots of RAM is needed (64 GB is not excessive).

There are some gn flags that can improve build speeds. You can specify these in the editor that appears when you create your output directory (gn args out/Default) or on the gn gen command line (gn gen out/Default --args="is_component_build = true is_debug = true"). Some helpful settings to consider using include:

  • use_jumbo_build = true - experimental Jumbo/unity builds.
  • is_component_build = true - this uses more, smaller DLLs, and incremental linking.
  • enable_nacl = false - this disables Native Client which is usually not needed for local builds.
  • target_cpu = "x86" - x86 builds are slightly faster than x64 builds and support incremental linking for more targets. Note that if you set this but don‘t’ set enable_nacl = false then build times may get worse.
  • remove_webcore_debug_symbols = true - turn off source-level debugging for blink to reduce build times, appropriate if you don't plan to debug blink.

In order to ensure that linking is fast enough we recommend that you use one of these settings - they all have tradeoffs:

  • use_lld = true - this linker is very fast on full links but does not support incremental linking.
  • is_win_fastlink = true - this option makes the Visual Studio linker run much faster, and incremental linking is supported, but it can lead to debugger slowdowns or out-of-memory crashes.
  • symbol_level = 1 - this option reduces the work the linker has to do but when this option is set you cannot do source-level debugging.

In addition, Google employees should use goma, a distributed compilation system. Detailed information is available internally but the relevant gn arg is:

  • use_goma = true

To get any benefit from goma it is important to pass a large -j value to ninja. A good default is 10*numCores to 20*numCores. If you run autoninja then it will automatically pass an appropriate -j value to ninja for goma or not.

$ autoninja -C out\Default chrome

When invoking ninja specify ‘chrome’ as the target to avoid building all test binaries as well.

Still, builds will take many hours on many machines.

Why is my build slow?

Many things can make builds slow, with Windows Defender slowing process startups being a frequent culprit. Have you ensured that the entire Chromium src directory is excluded from antivirus scanning (on Google machines this means putting it in a src directory in the root of a drive)? Have you tried the different settings listed above, including different link settings and -j values? Have you asked on the chromium-dev mailing list to see if your build is slower than expected for your machine's specifications?

The next step is to gather some data. There are several options. Setting NINJA_STATUS lets you configure Ninja's output so that, for instance, you can see how many processes are running at any given time, how long the build has been running, etc., as shown here:

$ set NINJA_STATUS=[%r processes, %f/%t @ %o/s : %es ] 
$ autoninja -C out\Default base
ninja: Entering directory `out\Default'
[1 processes, 86/86 @ 2.7/s : 31.785s ] LINK(DLL) base.dll base.dll.lib base.dll.pdb

In addition, if you set the NINJA_SUMMARIZE_BUILD environment variable to 1 then autoninja will print a build performance summary when the build completes, showing the slowest build steps and build-step types, as shown here:

$ autoninja -C out\Default base
    Longest build steps:
           1.2 weighted s to build base.dll, base.dll.lib, base.dll.pdb (1.2 s CPU time)
           8.5 weighted s to build obj/base/base/base_jumbo_38.obj (30.1 s CPU time)
    Time by build-step type:
           1.2 s weighted time to generate 1 PEFile (linking) files (1.2 s CPU time)
          30.3 s weighted time to generate 45 .obj files (688.8 s CPU time)
    31.8 s weighted time (693.8 s CPU time, 21.8x parallelism)
    86 build steps completed, average of 2.71/s

You can also generate these reports by manually running the script after a build:

$ python depot_tools\ -C out\Default

You can also get a visual report of the build performance with ninjatracing. This converts the .ninja_log file into a .json file which can be loaded into chrome://tracing:

$ python ninjatracing out\Default\.ninja_log >build.json

Finally, Ninja can report on its own overhead which can be helpful if, for instance, process creation is making builds slow, perhaps due to antivirus interference due to clang-cl not being in an excluded directory:

$ autoninja -d stats -C out\Default base
metric                  count   avg (us)        total (ms)
.ninja parse            3555    1539.4          5472.6
canonicalize str        1383032 0.0             12.7
canonicalize path       1402349 0.0             11.2
lookup node             1398245 0.0             8.1
.ninja_log load         2       118.0           0.2
.ninja_deps load        2       67.5            0.1
node stat               2516    29.6            74.4
depfile load            2       1132.0          2.3
StartEdge               88      3508.1          308.7
FinishCommand           87      1670.9          145.4
CLParser::Parse         45      1889.1          85.0

Build Chromium

Build Chromium (the “chrome” target) with Ninja (or autoninja) using the command:

$ ninja -C out\Default chrome

You can get a list of all of the other build targets from GN by running gn ls out/Default from the command line. To compile one, pass to Ninja the GN label with no preceding “//” (so for //chrome/test:unit_tests use ninja -C out/Default chrome/test:unit_tests`).

Run Chromium

Once it is built, you can simply run the browser:

$ out\Default\chrome.exe

(The “.exe” suffix in the command is actually optional).

Running test targets

You can run the tests in the same way. You can also limit which tests are run using the --gtest_filter arg, e.g.:

$ out\Default\unit_tests.exe --gtest_filter="PushClientTest.*"

You can find out more about GoogleTest at its GitHub page.

Update your checkout

To update an existing checkout, you can run

$ git rebase-update
$ gclient sync

The first command updates the primary Chromium source repository and rebases any of your local branches on top of tip-of-tree (aka the Git branch origin/master). If you don't want to use this script, you can also just use git pull or other common Git commands to update the repo.

The second command syncs the subrepositories to the appropriate versions and re-runs the hooks as needed.