linux: add a gdb pretty-print module for WebCore types

Now I can see e.g. Indic scripts in my string literals while debugging.

Review URL: http://codereview.chromium.org/548019

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@36288 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 96 insertions, 0 deletions

diff --git a/tools/gdb/webkit.py b/tools/gdb/webkit.py
new file mode 100644
index 0000000..2e1cf12
--- /dev/null
+++ b/tools/gdb/webkit.py
@@ -0,0 +1,96 @@
+# Copyright (c) 2010 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""GDB support for WebKit types.
+
+Add this to your gdb by amending your ~/.gdbinit as follows:
+  python
+  import sys
+  sys.path.insert(0, "/path/to/tools/gdb/")
+  import webkit
+"""
+
+import gdb
+import struct
+
+def ustring_to_string(ptr, length=None):
+    """Convert a pointer to UTF-16 data into a Python Unicode string.
+
+    ptr and length are both gdb.Value objects.
+    If length is unspecified, will guess at the length."""
+    extra = ''
+    if length is None:
+        # Try to guess at the length.
+        for i in xrange(0, 2048):
+            if int((ptr + i).dereference()) == 0:
+                length = i
+                break
+        if length is None:
+            length = 256
+            extra = u' (no trailing NUL found)'
+    else:
+        length = int(length)
+
+    char_vals = [int((ptr + i).dereference()) for i in xrange(length)]
+    string = struct.pack('H' * length, *char_vals).decode('utf-16', 'replace')
+
+    return string + extra
+
+
+class StringPrinter:
+    "Shared code between different string-printing classes"
+    def __init__(self, val):
+        self.val = val
+
+    def display_hint(self):
+        return 'string'
+
+
+class UCharStringPrinter(StringPrinter):
+    "Print a UChar*; we must guess at the length"
+    def to_string(self):
+        return ustring_to_string(self.val)
+
+
+class WebCoreAtomicStringPrinter(StringPrinter):
+    "Print a WebCore::AtomicString"
+    def to_string(self):
+        return self.val['m_string']
+
+
+class WebCoreStringPrinter(StringPrinter):
+    "Print a WebCore::String"
+    def get_length(self):
+        if not self.val['m_impl']['m_ptr']:
+            return 0
+        return self.val['m_impl']['m_ptr']['m_length']
+
+    def to_string(self):
+        if self.get_length() == 0:
+            return '(null)'
+
+        return ustring_to_string(self.val['m_impl']['m_ptr']['m_data'],
+                                 self.get_length())
+
+
+def lookup_function(val):
+    """Function used to load pretty printers; will be passed to GDB."""
+    lookup_tag = val.type.tag
+    printers = {
+        "WebCore::AtomicString": WebCoreAtomicStringPrinter,
+        "WebCore::String": WebCoreStringPrinter,
+    }
+    name = val.type.tag
+    if name in printers:
+        return printers[name](val)
+
+    if val.type.code == gdb.TYPE_CODE_PTR:
+        name = str(val.type.target().unqualified())
+        if name == 'UChar':
+            return UCharStringPrinter(val)
+
+    return None
+
+
+gdb.pretty_printers.append(lookup_function)