GDB and WebKit

GDB 7 introduced Python scripting of GDB. Tools/gdb/webkit.py extends GDB with WebKit-specific knowledge. See the top of the file for info on how to add this to your GDB.

Pretty Printing

With the script in place, we can pretty-print WTF string classes. So, for example, I can now break in GDB and see:

(gdb) p run
$1 = (const WebCore::TextRun &) @0x7fffffffa450: {m_characters = "Plugin Testsa", m_len = 12, m_xpos = 0, 
  m_padding = 0, m_allowTabs = false, m_rtl = false, m_directionalOverride = false, 
  m_applyRunRounding = true, m_applyWordRounding = true, m_disableSpacing = false}

Where m_characters is a UChar*. (Note that because it's a raw pointer, we have to guess at the length of the string -- the m_len parameter there is the length this code probably ends up using. When pretty-printing a string object we get the length correct.)

To undo this pretty-printing, pass the /r switch to p, like so:

(gdb) p/r run.m_characters
$2 = (const UChar *) 0x3355130
(gdb) x/12hc run.m_characters
0x3355130:	80 'P'	108 'l'	117 'u'	103 'g'	105 'i'	110 'n'	32 ' '	84 'T'
0x3355140:	101 'e'	115 's'	116 't'	115 's'

Helper Functions

That script also adds a GDB command useful for printing WebKit Node trees.

printpathtoroot variable_name

will print the tree of nodes above a WebCore::Node.

Troubleshooting: GDB crashes on Linux

Ubuntu Karmic has a bug which causes gdb to crash on Linux when WebKit is compiled in debug mode. You can solve the crash by increasing stack size:

ulimit -s 65535