GN build configuration

GN build configuration
This page provides some common build setups for the GN build. It assumes you already  got a Chromium checkout.
See also

Run "gn help"from the command line.

All GN Docs

GN Quick Start Guide

GN Reference (a dump of everything from "gn help"in one web page).

Understanding GN build flags
Recall that in GN, you pick your own build directory. These should generally go in a subdirectory of 
src/out. You set build arguments on a build directory by typing:

$ gn args out/mybuild

This will bring up an editor. The format of the stuff in the args file is just GN code, so set variables according to normal GN syntax (true/false for booleans, double-quotes for string values, 
# for comments). When you close the editor, a build will be made in that directory. To change the arguments for an existing build, just re-run this command on the existing directory.
 
You can get a list of all available build arguments for a given build directory, with documentation, by typing

$ gn args out/mybuild --list

To get documentation for a single flag (in this example, 
is_component_build):

$ gn args out/mybuild --list=is_component_build

You have to list your build directory as the first argument because the available arguments and their default values are build-specific. For example, setting Android as your target OS might expose new Android-specific build arguments or use different default values.
 
"GN args"as used on this page are not the command line arguments passed to GN. They refer to the individual variables that are passed as part of the --args command line flag and/or written to the args.gn file.
Common build variants
Release build
The default GN build is debug. To do a release build:

is_debug = false

On Android, you can toggle ProGuard on/off with:

is_java_debug = false  # Defaults to is_debug.

Trybots that run release builds have DCHECKs enabled, to catch potential bugs.

dcheck_always_on = true

 
Component build
The  component build links many parts of Chrome into separate shared libraries to avoid the long link step at the end. It is the default when compiling debug non-iOS builds and most developers use this mode for everyday builds and debugging. Startup is slower and some linker optimizations won't work, so don't do benchmarks in this mode. Some people like to turn it on for release builds to get both faster links and reasonable runtime performance.

is_component_build = true

Faster builds with no symbols
Turning off symbols will make debugging almost impossible, but the build will be much faster. It can be useful in some cases where you just want a build ASAP (many build bots do this).

symbol_level = 0

Alternately you can set symbol_level=1 which will build almost as fast as symbol_level=0 but will give you function names in call stacks.
Disable Native Client
Most developers don't normally need to test Native Client capabilities and can speed up the build by disabling it.

enable_nacl = false

Remove WebCore symbols
WebCore has lots of templates that account for a large portion of the debugging symbols. If you're not debugging WebCore, you can skip these symbols to make the build smaller and faster:

blink_symbol_level=0

Overriding the CPU architecture
By default, the GN build will match that of the host OS and CPU architecture. To override:

target_cpu = "x86"

Possible values for the 
target_cpu:

Windows supports "x86" and "x64". Since building is only supported on 64-bit machines, the default will always be "x64".

Mac and desktop Linux supports only  "x64". On desktop Linux you might also theoretically try any of the ARM or MIPS architecture strings form the Android section below, but these aren't supported or tested and you will also need a sysroot.

Chrome OS supports "x86" and "x64", but to build a 32-bit binary you will need to use a sysroot on a 64-bit machine. 

If you specify an Android build (see below) the default CPU architecture will be "arm". You could try overriding it to "arm64", "x86", "mipsel", or "mips64el" but the GN builds for these aren't regularly tested.

Goma
Googlers can use this for distributed builds. goma_dir is only required if you put the Goma tools in a non-standard place (the default place is ~/goma or C:\goma\goma-win).

use_goma = true
goma_dir = "/home/me/somewhere/goma"  # Optional

 
Official Chrome build
This build requires that you are a Googler with 
src-internal checked out.
 
Use these args for official builds:

is_official_build = true
is_chrome_branded = true
is_debug = false

For 32-bit official builds, append this arg to the above set:

target_cpu = "x86"

 
Windows
There is a 'gn gen' argument (--ide) for producing Visual Studio project and solution files:

$ gn gen out\mybuild --ide=vs

Projects are configured for VS 2015 by default.
 
See  this page for more information on configuring Chromium builds for Windows.
Android build (from Linux)
This assumes you've already followed the  Android build instructions to check out. 

 
            
It is easy to use the same checkout on Linux to build both Android and desktop Linux versions of Chrome. Your .gclient file must list Android, however, to get the proper SDKs downloaded. This will happen automatically if you follow the Android checkout instructions. To add this to an existing Linux checkout, add target_os to your .gclient file (in the directory above src), and run gclient runhooks.
 
            
 
            
 
             
solutions = [
  ...existing stuff in here...
]
target_os = [ 'android' ] # Add this to get Android stuff checked out.
  
Chrome OS build (from Linux) 
This will build the Chrome OS variant of the browser that is distributed with the operating system. You can run it on your Linux desktop for feature development. 
target_os = "chromeos"
  
Checkouts which are used to build Chrome OS builds must also have  'chromeos'  added to the  target_os  list in the .gclient file. After making this change, you will need to run  gclient sync  once. 
solutions = [
   ...existing stuff in here...
]
target_os = ['chromeos']
# Or if you also build e.g. android, this might be
# target_os = ['android', 'chromeos']