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See ImprovingLifeOnWindows for ideas about how to make developing WebKit on Windows easier.

Building on Windows

Follow the instructions on to install the necessary developer tools, support libraries, and check out the WebKit code.

Note that it is safest to build WebKit in your Cygwin home directory. At the moment, there seems to be an implicit assumption in the build scripts that paths will be relative to the home directory.

Building from within Visual Studio

WebKit can be built from within Visual Studio by setting two environment variables:

  • WEBKITOUTPUTDIR - An absolute Windows-style path pointing to the directory where you want the build products to go.
  • WEBKITLIBRARIESDIR - An absolute Windows-style path pointing to the WebKitLibraries/win folder in your WebKit checkout.

These environment variables should be set for you the first time you run update-webkit.

Common Build Errors

Error spawning cmd.exe / Linker errors

Sometimes, Visual Studio complains that it 'cannot spawn cmd.exe'. Should this happen, check if both your Cygwin\bin folder and c:\windows\sytem32 are in the Visual Studio list of executable files (Tools -> Options -> VC++ Directories) and that your Cygwin\bin appears after the Visual Studio bin folders (Otherwise, the wrong link.exe will be used; that is, the Cygwin link.exe will be used instead of the Visual Studio tool of the same name).

Missing Autogenerated Files

If you have the Visual Studio IDE open while you are performing an update-webkit, you can sometimes run into a strange problem where Visual Studio is unable to locate the autogenerated files. These files are usually things like HTMLNames.cpp, which are generated by Perl as part of the WebCoreGenerated target.

The best way to resolve this is to exit from the IDE, then relaunch. This usually fixes the problem, though you may wish to clean and rebuild the JavaScriptCoreGenerated and WebCoreGenerated projects.

Bad line endings

When you see errors in WebCore/css/makeprops or WebCore/css/maketokenizer, open those files in a suitable editor (SciTE works) and convert the line endings to LF only (Unix-style). Then restart the build.

Visual Studio 2005

Early versions of Visual Studio 2005 are missing the library 'Crypt32.lib'. A workaround is to download and install the Windows Server 2003 R2 Platform SDK then copy the file 'Crypt32.lib' from the directory C:\Program Files\Microsoft Platform SDK for Windows Server 2003 R2\Lib to %VSINSTALLDIR%\VC\PlatformSDK\Lib.

Visual C++ Express Edition

1>c:\cygwin\home\admin\webkit\javascriptcore\wtf\assertions.cpp(45) : fatal error C1083: Cannot open include file: 'windows.h': No such file or directory

If you see errors like this you probably need to install the platform SDK.

Project : error PRJ0002 : Error result -1073741515 returned from 'c:\Program Files\Microsoft Visual Studio 8\VC\bin\cl.exe'

If you see this error and/or when you manually execute c:\Program Files\Microsoft Visual Studio 8\VC\bin\cl.exe you see the error message "This application has failed to start because mspdb80.dll was not found. Re-installing the application may fix this problem" then you need to ensure that the directory C:\Program Files\Microsoft Visual Studio 8\Common7\IDE is listed in the PATH environment variable.


If you see errors opening the WebKit solution in Visual Studio/Visual C++ Express that say:

"$(WebKitLibrariesDir)/tools/vsprops/common.vsprops could not be found or failed to load"

(or some other .vsprops file), you must set the "WebKitLibrariesDir" environment variable. Make sure that "WebKitLibrariesDir" points to the "WebKitLibraries/win" directory, not the "WebKitLibraries/" directory.

Missing packages in Cygwin

You may have had cygwin already installed before attempting to build WebKit. In this case, you should have checked your cygwin setup to make sure that you have at least the following packages installed: bison, gawk, flex, gperf, perl, zlib. The error reports you get when you miss one such package are particularly cryptic and may not lead you to those packages.

If you'd rather reconcile each package and version manually, rather than use the cygwin installer, you may find the list of packages included in the cygwin installer useful.

Other Common Errors

Perl warnings when you run run-webkit-tests

If you see Perl warnings when you run run-webkit-tests of the form:

readline() on closed filehandle INSTALL_DIR at /home/Administrator/Tools/Scripts/ line 1536.
Use of uninitialized value $path in substitution (s///) at /home/Administrator/Tools/Scripts/ line 1537.
Use of uninitialized value $path in concatenation (.) or string at /home/Administrator/Tools/Scripts/ line 1540.

then you must install Safari 4.0.4 or greater.

Error launching Apache from run-webkit-tests on Vista/7, or other errors that mention the word "remap"

You need to rebase some DLLs. Do the following:

  1. From a Cygwin terminal, run:
    find /bin /usr/bin /lib /usr/lib "$(realpath WebKit/OpenSource/LayoutTests/http/conf)" \( -iname cyglsa64.dll -o -iname cygwin1.dll \) -o -iname '*.dll' -print > /tmp/rebaselist
  2. Kill all Cygwin processes
  3. Run the following command via Start > Run:
    c:\cygwin\bin\ash -c "/bin/rebaseall -T /tmp/rebaselist"

Debugging information cannot be found

When following the instructions on on how to debug WebKit on Windows, Visual Studio displays the message:

"Debugging information for 'Safari.exe' cannot be found or does not match. No symbols loaded."

If you look at the modules, you should should see that symbols were loaded for JavaScriptCore.dll and WebKit.dll. In this case, you may safely ignore that message.

If not, check that you followed the instructions on how to configure Visual Studio to use Apple's Safari for Windows symbol server on the bottom of

Cannot find SafariTheme.dll

Make sure that Safari (e.g. C:\Program Files (x86)\Safari) is included in your 'Path' System Environment variable.

Running the Layout Tests on Windows

Getting Crash Logs

run-webkit-tests can save crash logs when a crash occurs during a test. To set this up:

  1. Install Debugging Tools for Windows 32-bit Version
  2. Set the _NT_SYMBOL_PATH environment variable to include both the Microsoft and Safari symbol servers. It should look something like cache*c:\symbols;SRV*;SRV*http://url.for.safari/symbol/server. (See this page for the URL of the Safari symbol server.)
  3. Disable User Account Control if you are using Windows Vista (instructions) or Windows 7 (instructions). (See Bug 44135 for details.)

Tweaks to run tests

Running the layout-tests without failures requires a few tweaks to the environment:

Audio-related failures

Install QuickTime

Font-metric-related failures

Running layout-test on Windows requires a set of fonts not normally bundled with Windows. The full list of required fonts can be found here:

Most of these fonts come from OS X, so they can't be freely redistributed as one font-package for testing-purposes.

They can however be copied from your Mac (if you have one), but they have to be converted into a TrueType format Windows understands.

Look in /System/Library/Fonts and /Library/Fonts for the source files.

The rest of the fonts can be found here:

The easiest approach is to convert all these fonts to Windows-style TrueType fonts and put them in a single folder. Then point the WEBKIT_TESTFONTS environment variable to that directory when running run-webkit-tests.

Note however that you might still see metric-related failures (if anyone knows why, please update this section with more complete instructions).

Problems with Python auto-update

You may encounter errors when the build environment attempts to install Python modules when running Cygwin in a Windows host OS inside a VMWare instance. The errors will look like the following:

webkitpy.common.system.autoinstall: INFO     Auto-installing package:
webkitpy.common.system.autoinstall: INFO         From: "
webkitpy.common.system.autoinstall: INFO           To: "/cygdrive/e/Projects/Web
Traceback (most recent call last):
  File "/cygdrive/e/Projects/WebKit/Tools/Scripts/test-webkitpy", line 266, in <
    Tester().run_tests(sys.argv, external_package_paths)
  File "/cygdrive/e/Projects/WebKit/Tools/Scripts/webkitpy/test/", line 1

This seems to happen when running VMWare in NAT networking mode. If you switch to Bridged networking, everything should work properly.

Debugging DumpRenderTree on Windows

To debug DumpRenderTree on Windows, see Debugging DumpRenderTree on Windows?.

Running WebKit.dll-derived Apps on Windows

In order for your application to properly derive MIME types for local files (i.e. when you supply a "file:" URL), be sure that there is a "\CFNetwork.resources" directory in the same directory as CoreFoundation.dll. CFNetwork.resources must contain a file, types.plist, an XML parameter list that describes the mapping of file extensions to MIME types. You'll also need Info.plist from this directory, but you won't need the *.lproj subdirectories. You can find the aforementioned directory and files in the same place as you found CoreFoundation.dll in the first place. Typically, a Safari installation will install it at

C:\Program Files\Common Files\Apple\Apple Application Support\CFNetwork.resources