Add support for core JSC types to lldb_webkit.py

https://bugs.webkit.org/show_bug.cgi?id=294220
rdar://152866196

Reviewed by Yusuke Suzuki.

This patch adds support for core JSC types, specifically JSValue,
EncodedJSValue, JSCell, and JSString to lldb_webkit.py, so that
the debugger shows descriptive summaries when displaying values
of those types.

* Tools/lldb/lldb_webkit.py:
(__lldb_init_module):
(WTFMediaTimeProvider.hasDoubleValue):
(SummarizeJSValue):
(SummarizeEncodedJSValue):
(SummarizeJSString):
(JSValueMirror):
(JSValueMirror.__init__):
(JSValueMirror.isNull):
(JSValueMirror.isUndefined):
(JSValueMirror.isEmpty):
(JSValueMirror.isBool):
(JSValueMirror.isTrue):
(JSValueMirror.isFalse):
(JSValueMirror.isInt32):
(JSValueMirror.isNumber):
(JSValueMirror.isDouble):
(JSValueMirror.isCell):
(JSValueMirror.toInt32):
(JSValueMirror.toDouble):
(JSValueMirror.summary):
(JSCellMirror):
(JSCellMirror.__init__):
(JSCellMirror.enumMemberValue):
(JSCellMirror.enumMemberName):
(JSCellMirror.isString):
(JSCellMirror.isObject):
(JSCellMirror.isCustomGetterSetter):
(JSCellMirror.summary):
(JSStringMirror):
(JSStringMirror.__init__):
(JSStringMirror.isRopeString):
(JSStringMirror.summary):
(JSStringMirror.maybeTrim):
(castSBValueToPointerType):
(hexPointerString):

Canonical link: https://commits.webkit.org/296021@main

Author: ast-hugger

Tools/lldb/lldb_webkit.py

@@ -29,6 +29,7 @@
 
 """
 
+import ctypes
 import re
 import string
 import struct
@@ -90,6 +91,10 @@ def __lldb_init_module(debugger, dict):
     debugger.HandleCommand('type summary add --expand -F lldb_webkit.WTFOptionSet_SummaryProvider -x "^WTF::OptionSet<.+>$"')
     debugger.HandleCommand('type summary add --expand -F lldb_webkit.WTFCompactPointerTuple_SummaryProvider -x "^WTF::CompactPointerTuple<.+,.+>$"')
 
+    debugger.HandleCommand('type summary add --expand -F lldb_webkit.SummarizeEncodedJSValue JSC::EncodedJSValue')
+    debugger.HandleCommand('type summary add --expand -F lldb_webkit.SummarizeJSString JSC::JSString')
+    debugger.HandleCommand('type summary add --expand -F lldb_webkit.SummarizeJSValue JSC::JSValue')
+
     debugger.HandleCommand('type summary add -F lldb_webkit.WTFURL_SummaryProvider WTF::URL')
     debugger.HandleCommand('type summary add -F lldb_webkit.WebCoreColor_SummaryProvider WebCore::Color')
 
@@ -1301,3 +1306,200 @@ def isIndefinite(self):
 
     def hasDoubleValue(self):
         return self.valobj.GetChildMemberWithName('m_timeFlags').GetValueAsSigned(0) & (1 << 5)
+
+
+def SummarizeJSValue(valobj, dict):
+    mirror = JSValueMirror(valobj)
+    return mirror.summary()
+
+
+def SummarizeEncodedJSValue(valobj, dict):
+    mirror = JSValueMirror(valobj, valobj.GetValueAsUnsigned(0))
+    return mirror.summary()
+
+
+def SummarizeJSString(valobj, dict):
+    mirror = JSStringMirror(valobj)
+    return mirror.summary()
+
+
+class JSValueMirror:
+    """Reflects on a JSValue or EncodedJSValue."""
+
+    OTHER_TAG     = 0b0010
+    BOOL_TAG      = 0b0100
+    UNDEFINED_TAG = 0b1000
+
+    NATIVE_CALLEE_TAG   = OTHER_TAG | 1
+    NATIVE_CALLEE_MASK  = 0b0111
+
+    TOP_15_BITS_MASK        = 0xFFFE << 48
+    TOP_15_BITS_POINTER_TAG = 0
+    TOP_15_BITS_INTEGER_TAG     = 0xFFFE << 48
+
+    NUMBER_TAG = 0xFFFE000000000000
+    MISC_TAG = OTHER_TAG | BOOL_TAG | UNDEFINED_TAG
+
+    NOT_CELL_MASK = NUMBER_TAG | OTHER_TAG
+
+    VALUE_NULL      = OTHER_TAG
+    VALUE_UNDEFINED = OTHER_TAG | UNDEFINED_TAG
+    VALUE_TRUE      = OTHER_TAG | BOOL_TAG | 1
+    VALUE_FALSE     = OTHER_TAG | BOOL_TAG | 0
+
+    VALUE_EMPTY     = 0
+    VALUE_DELETED   = 4
+
+    def __init__(self, valobj, bits=None):
+        assert valobj.GetTypeName() == "JSC::JSValue" or valobj.GetTypeName() == "JSC::EncodedJSValue"
+        self.valobj = valobj
+        self.bits = bits if bits is not None else valobj.GetChildMemberWithName("u").GetChildMemberWithName("asInt64").GetValueAsUnsigned(0)
+
+    def isNull(self):
+        return self.bits == self.VALUE_NULL
+
+    def isUndefined(self):
+        return self.bits == self.VALUE_UNDEFINED
+
+    def isEmpty(self):
+        return self.bits == self.VALUE_EMPTY
+
+    def isBool(self):
+        return self.bits & ~1 == self.VALUE_FALSE
+
+    def isTrue(self):
+        return self.bits == self.VALUE_TRUE
+
+    def isFalse(self):
+        return self.bits == self.VALUE_TRUE
+
+    def isInt32(self):
+        return self.bits & self.NUMBER_TAG == self.NUMBER_TAG
+
+    def isNumber(self):
+        return self.bits & self.NUMBER_TAG != 0
+
+    def isDouble(self):
+        return self.isNumber() and not self.isInt32()
+
+    def isCell(self):
+        return self.bits & self.NOT_CELL_MASK == 0
+
+    def toInt32(self):
+        assert self.isInt32()
+        masked = self.bits & 0xFFFFFFFF
+        if masked > 0x80000000:
+            return masked - 0x100000000  # => -1
+        else:
+            return masked
+
+    def toDouble(self):
+        assert self.isDouble()
+        corrected = self.bits - (1 << 49)
+        return struct.unpack('<d', corrected.to_bytes(8, 'little'))[0]
+
+    def summary(self):
+        if self.isCell():
+            cell = castSBValueToPointerType("JSC::JSCell", self.valobj)
+            mirror = JSCellMirror(cell, self.bits)
+            return mirror.summary()
+        if self.isNull():
+            return "{JS null}"
+        if self.isUndefined():
+            return "{JS undefined}"
+        if self.isTrue():
+            return "{JS true}"
+        if self.isFalse():
+            return "{JS false}"
+        if self.isEmpty():
+            return "{JS empty}"
+        if self.isInt32():
+            return f"{{JS int32={self.toInt32()}}}"
+        if self.isDouble():
+            return f"{{JS double={self.toDouble()}}}"
+        return "{JSC ?}"
+
+
+class JSCellMirror:
+    def __init__(self, valobj, bits):
+        assert valobj.GetTypeName() == "JSC::JSCell *"
+        self.valobj = valobj
+        self.bits = bits
+        self.type = valobj.GetChildMemberWithName("m_type").GetValueAsUnsigned(0)
+        typeEnum = valobj.GetTarget().FindFirstType("JSC::JSType")
+        self.enumMembers = typeEnum.GetEnumMembers()
+
+    def enumMemberValue(self, enumMemberName):
+        return self.enumMembers[enumMemberName].unsigned
+
+    def enumMemberName(self, enumMemberValue):
+        # try bisecting first, but it that fails give it another try linearly just to be sure
+        index = bisect_right(self.enumMembers, enumMemberValue, key=lambda mem: mem.unsigned)
+        guess = self.enumMembers[index - 1]
+        if guess.unsigned == enumMemberValue:
+            return guess.name
+        for member in self.enumMembers:
+            if member.unsigned == enumMemberValue:
+                return member.name
+        return "?"
+
+    def isString(self):
+        return self.type == self.enumMemberValue("StringType")
+
+    def isObject(self):
+        return self.type >= self.enumMemberValue("ObjectType")
+
+    def isCustomGetterSetter(self):
+        return self.type == self.enumMemberValue("CustomGetterSetterType")
+
+    def summary(self):
+        if self.isString():
+            string = castSBValueToPointerType("JSC::JSString", self.valobj)
+            mirror = JSStringMirror(string)
+            return mirror.summary(verbose=False)
+        if self.isObject():
+            return "{JS object %s}" % (self.enumMemberName(self.type))
+        return "{{JS cell %s}}}" % (self.enumMemberName(self.type))
+
+
+class JSStringMirror:
+    def __init__(self, valobj):
+        assert valobj.GetTypeName() == "JSC::JSString *"
+        self.fiber = valobj.GetChildMemberWithName("m_fiber")
+
+    def isRopeString(self):
+        return self.fiber.GetValueAsUnsigned(0) & 1 != 0
+
+    def summary(self, verbose=True):
+        provider = WTFStringImplProvider(self.fiber, {})
+        if not provider.is_initialized():
+            raise RuntimeError("null fiber pointer in JSString mirror")
+        contents = self.maybeTrim(provider.to_string())
+        if verbose:
+            bitCount = 8 if provider.is_8bit() else 16
+            if self.isRopeString():
+                return '{JS ropeString bits=%d fiber1 length=%d %s ...}' % (bitCount, provider.get_length(), contents)
+            else:
+                return '{JS string bits=%d length=%d %s}' % (bitCount, provider.get_length(), contents)
+        else:
+            if self.isRopeString():
+                return '{JS ropeString fiber1=%s}' % (contents)
+            else:
+                return '{JS string %s}' % (contents)
+
+    def maybeTrim(self, string):
+        escaped = repr(string)
+        if len(escaped) > 90:
+            return f'{escaped[:80]} [... trimmed]'
+        else:
+            return escaped
+
+
+def castSBValueToPointerType(typeName, value):
+    ptrType = value.GetTarget().FindFirstType(typeName).GetPointerType()
+    return value.Cast(ptrType)
+
+
+def hexPointerString(bits):
+    """Convert bits, which is an unsigned integer, to a string that would be produced by %p in C."""
+    return f"{bits:#0{2 + ctypes.sizeof(ctypes.c_void_p) * 2}x}"