new synthetic children provider for CFString and related classes ; test case for it

llvm-svn: 136525

Author: egranata

lldb/examples/synthetic/CFString.py

@@ -0,0 +1,206 @@
+# synthetic children provider for CFString
+# (and related NSString class)
+import lldb
+class CFStringSynthProvider:
+	def __init__(self,valobj,dict):
+		self.valobj = valobj;
+		self.update()
+	# children other than "content" are for debugging only and must not be used in production code
+	def num_children(self):
+		return 6;
+	def read_unicode(self, pointer):
+		process = self.valobj.GetTarget().GetProcess()
+		error = lldb.SBError()
+		pystr = u''
+		# cannot do the read at once because the length value has
+		# a weird encoding. better play it safe here
+		while True:
+			content = process.ReadMemory(pointer, 2, error)
+			new_bytes = bytearray(content)
+			b0 = new_bytes[0]
+			b1 = new_bytes[1]
+			pointer = pointer + 2
+			if b0 == 0 and b1 == 0:
+				break
+			# rearrange bytes depending on endianness
+			# (do we really need this or is Cocoa going to
+			#  use Windows-compatible little-endian even
+			#  if the target is big endian?)
+			if self.is_little:
+				value = b1 * 256 + b0
+			else:
+				value = b0 * 256 + b1
+			pystr = pystr + unichr(value)
+		return pystr
+	# handle the special case strings
+	# only use the custom code for the tested LP64 case
+	def handle_special(self):
+		if self.lp64 == False:
+			# for 32bit targets, use safe ObjC code
+			return self.handle_unicode_string_safe()
+		offset = 12
+		pointer = int(self.valobj.GetValue(), 0) + offset
+		pystr = self.read_unicode(pointer)
+		return self.valobj.CreateValueFromExpression("content",
+			"(char*)\"" + pystr.encode('utf-8') + "\"")
+	# last resort call, use ObjC code to read; the final aim is to
+	# be able to strip this call away entirely and only do the read
+	# ourselves
+	def handle_unicode_string_safe(self):
+		return self.valobj.CreateValueFromExpression("content",
+			"(char*)\"" + self.valobj.GetObjectDescription() + "\"");
+	def handle_unicode_string(self):
+		# step 1: find offset
+		if self.inline:
+			pointer = int(self.valobj.GetValue(), 0) + self.size_of_cfruntime_base();
+			if self.explicit == False:
+				# untested, use the safe code path
+				return self.handle_unicode_string_safe();
+			else:
+				# not sure why 8 bytes are skipped here
+				# (lldb) mem read -c 50 0x00000001001154f0
+				# 0x1001154f0: 98 1a 85 71 ff 7f 00 00 90 07 00 00 01 00 00 00  ...q?...........
+				# 0x100115500: 03 00 00 00 00 00 00 00 *c3 03 78 00 78 00 00 00  ........?.x.x...
+				# 0x100115510: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
+				# 0x100115520: 00 00                                            ..
+				# content begins at * (i.e. 8 bytes into variants, skipping void* buffer in
+				# __notInlineImmutable1 entirely, while the length byte is correctly located
+				# for an inline string)
+				pointer = pointer + 8;
+		else:
+			pointer = int(self.valobj.GetValue(), 0) + self.size_of_cfruntime_base();
+			# read 8 bytes here and make an address out of them
+			vopointer = self.valobj.CreateChildAtOffset("dummy",
+				pointer,self.valobj.GetType().GetBasicType(lldb.eBasicTypeChar).GetPointerType());
+			pointer = int(vopointer.GetValue(), 0)
+		# step 2: read Unicode data at pointer
+		pystr = self.read_unicode(pointer)
+		# step 3: return it
+		return self.valobj.CreateValueFromExpression("content",
+			"(char*)\"" + pystr.encode('utf-8') + "\"")
+	# we read at "the right place" into the __CFString object instead of running code
+	# we are replicating the functionality of __CFStrContents in CFString.c here
+	def handle_UTF8_inline(self):
+		offset = int(self.valobj.GetValue(), 0) + self.size_of_cfruntime_base();
+		if self.explicit == False:
+			offset = offset + 1;
+		return self.valobj.CreateValueFromAddress("content",
+				offset, self.valobj.GetType().GetBasicType(lldb.eBasicTypeChar));
+	def handle_UTF8_not_inline(self):
+		offset = self.size_of_cfruntime_base();
+		return self.valobj.CreateChildAtOffset("content",
+				offset,self.valobj.GetType().GetBasicType(lldb.eBasicTypeChar).GetPointerType());
+	def get_child_at_index(self,index):
+		if index == 0:
+			return self.valobj.CreateValueFromExpression("mutable",
+				str(int(self.mutable)));
+		if index == 1:
+			return self.valobj.CreateValueFromExpression("inline",
+				str(int(self.inline)));
+		if index == 2:
+			return self.valobj.CreateValueFromExpression("explicit",
+				str(int(self.explicit)));
+		if index == 3:
+			return self.valobj.CreateValueFromExpression("unicode",
+				str(int(self.unicode)));
+		if index == 4:
+			return self.valobj.CreateValueFromExpression("special",
+				str(int(self.special)));
+		if index == 5:
+			if self.unicode == True:
+				return self.handle_unicode_string();
+			elif self.special == True:
+				return self.handle_special();
+			elif self.inline == True:
+				return self.handle_UTF8_inline();
+			else:
+				return self.handle_UTF8_not_inline();
+	def get_child_index(self,name):
+		if name == "content":
+			return self.num_children() - 1;
+		if name == "mutable":
+			return 0;
+		if name == "inline":
+			return 1;
+		if name == "explicit":
+			return 2;
+		if name == "unicode":
+			return 3;
+		if name == "special":
+			return 4;
+	def is_64bit(self):
+		if self.valobj.GetTarget().GetProcess().GetAddressByteSize() == 8:
+			return True;
+		else:
+			return False;
+	def is_little_endian(self):
+		# 4 is eByteOrderLittle
+		if self.valobj.GetTarget().GetProcess().GetByteOrder() == 4:
+			return True;
+		else:
+			return False;
+	# CFRuntimeBase is defined as having an additional
+	# 4 bytes (padding?) on LP64 architectures
+	# to get its size we add up sizeof(pointer)+4
+	# and then add 4 more bytes if we are on a 64bit system
+	def size_of_cfruntime_base(self):
+		if self.lp64 == True:
+			return 8+4+4;
+		else:
+			return 4+4;
+	# the info bits are part of the CFRuntimeBase structure
+	# to get at them we have to skip a uintptr_t and then get
+	# at the least-significant byte of a 4 byte array. If we are
+	# on big-endian this means going to byte 3, if we are on
+	# little endian (OSX & iOS), this means reading byte 0
+	def offset_of_info_bits(self):
+		if self.lp64 == True:
+			offset = 8;
+		else:
+			offset = 4;
+		if self.is_little == False:
+			offset = offset + 3;
+		return offset;
+	def read_info_bits(self):
+		cfinfo = self.valobj.CreateChildAtOffset("cfinfo",
+					self.offset_of_info_bits(),
+					self.valobj.GetType().GetBasicType(lldb.eBasicTypeChar));
+		cfinfo.SetFormat(11)
+		info = cfinfo.GetValue();
+		return int(info,0);
+	# calculating internal flag bits of the CFString object
+	# this stuff is defined and discussed in CFString.c
+	def is_mutable(self):
+		return (self.info_bits & 1) == 1;
+	def is_inline(self):
+		return (self.info_bits & 0x60) == 0;
+	# this flag's name is ambiguous, it turns out
+	# we must skip a length byte to get at the data
+	# when this flag is False
+	def has_explicit_length(self):
+		return (self.info_bits & (1 | 4)) != 4;
+	# probably a subclass of NSString. obtained this from [str pathExtension]
+	# here info_bits = 0 and Unicode data at the start of the padding word
+	# in the long run using the isa value might be safer as a way to identify this
+	# instead of reading the info_bits
+	def is_special_case(self):
+		return self.info_bits == 0;
+	def is_unicode(self):
+		return (self.info_bits & 0x10) == 0x10;
+	# preparing ourselves to read into memory
+	# by adjusting architecture-specific info
+	def adjust_for_architecture(self):
+		self.lp64 = self.is_64bit();
+		self.is_little = self.is_little_endian();
+	# reading info bits out of the CFString and computing
+	# useful values to get at the real data
+	def compute_flags(self):
+		self.info_bits = self.read_info_bits();
+		self.mutable = self.is_mutable();
+		self.inline = self.is_inline();
+		self.explicit = self.has_explicit_length();
+		self.unicode = self.is_unicode();
+		self.special = self.is_special_case();
+	def update(self):
+		self.adjust_for_architecture();
+		self.compute_flags();