Changes between Initial Version and Version 1 of Debugging With LLDB or GDB

Timestamp:

Mar 2, 2014 6:11:36 PM (10 years ago)

Author:

BJ Burg

Comment:

--

Debugging With LLDB or GDB

@@ +1 @@
+= Debugging WebKit2 =
+
+= Debugging DumpRenderTree =
+
+ 1. `build-webkit --debug`
+ 1. `build-dumprendertree --debug`
+ 1. `export DYLD_FRAMEWORK_PATH=/path/to/WebKit/WebKitBuild/Debug`
+ 1. `gdb --args WebKitBuild/Debug/DumpRenderTree /path/to/testfile.html`
+
+For LLDB, instead invoke using:
+
+`lldb -f WebKitBuild/Debug/DumpRenderTree -- /path/to/testfile.html`
+
+= Debugging WebKitTestRunner =
+
+= Miscellaneous Tips =
+
+== Shell Aliases ==
+
+The following will automate launching and running DRT under GDB with a specific test argument. You can use it like so: `wkd-drt path/to/test`
+{{{
+alias wkd-drt='(echo r; cat) | DYLD_FRAMEWORK_PATH=WebKitBuild/Debug gdb --args WebKitBuild/Debug/DumpRenderTree'
+}}}
+
+== WebKit-specific Scripts ==
+
+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. The LLDB equivalent is located at `Tools/lldb/lldb_webkit.py`.
+
+== 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
+}}}