• ​General information on using Xcode
• ​The main WebKit debug information

Debugging WebKit2

Method #1

1. Make sure Use WebKit2 for New Windows option is selected in Safari’s Debug
2. Open WebKit2.xcodeproj and make sure that the WebProcess is set to the Active Executable
3. Control-click the WebProcess executable and choose Get Info
4. In the Debugging tab, select Wait for next launch/push notification
5. Choose Run ► Debug
6. A dialog will appear saying: “Waiting for WebProcess to launch…”
7. Open Safari.xcodeproj Run ► Debug
8. The WebProcess will break in the debugger, and you’ll probably have to continue at least once before normal execution resumes

You’re now debugging both the UIProcess and the WebProcess. Your breakpoints in either should be work accordingly.

Method #2

1. Open the Xcode projects for Safari and WebCore (or WebKit2, or whatever)
2. From the Safari project, Run
3. From the WebCore project, choose Run ► Attach to Process, and choose the WebProcess
4. Let gdb do its thing, and Continue

You’re now debugging the WebProcess. (Note: I've had issues with gdb using this method.)

Debugging DumpRenderTree

TODO

Debugging WebKitTestRunner

Some code that executes during initialization can be hard to debug with the default way of attaching to the child process. In this situation, the following steps allowed Xcode to attach fairly early:

1. Set a breakpoint in the WebCore/WK2 WebProcess code you are interested in.
2. Set a breakpoint in TestInvocation::invoke.
3. Start WebKitTestRunner with the desired arguments.
4. Hit the breakpoint inside invoke().
5. Attach to the spawned web process (at the time of writing, named com.apple.WebKit.WebContent.Development.
6. Continue

Miscellaneous Tips

Prevent Safari from complaining about web process hangs when debugging

1. Control-click the Safari executable and choose Get Info
2. Select the Arguments tab
3. Beneath the list Variables to be set in the environment, click the “✚” button
4. Add the following item:
   • Name: DebugInitialDelayForUnresponsiveWebProcess
   • Value: 99999999

To debug a web process crash on launch:

1. Edit WebKit2/UIProcess/Launcher/mac/ProcessLauncherMac.mm
2. Search for SIGCONT
3. Remove the line of code that sends SIGCONT to the web process, then build
4. In Terminal:
   1. launch gdb, then type attach WebProcess — OR
   2. in Xcode select Run ► Attach to Process ► Process ID... and type the WebProcess’s process ID
5. Once attached:
   1. In gdb type continue«enter» — OR
   2. In Xcode select Run ► Continue

To debug a web process using Instruments/DTrace:

If you’re having trouble attaching to the WebProcess, try disabling the sandbox:

defaults write com.apple.WebProcess DisableSandbox YES