Adding upstream version 86.0.1.upstream/86.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 232 insertions, 0 deletions

diff --git a/js/src/gdb/mozilla/jsval.py b/js/src/gdb/mozilla/jsval.py
new file mode 100644
index 0000000000..022e59b363
--- /dev/null
+++ b/js/src/gdb/mozilla/jsval.py
@@ -0,0 +1,232 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this file,
+# You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# Pretty-printers for SpiderMonkey's JS::Value.
+
+import gdb
+import gdb.types
+import struct
+import mozilla.prettyprinters
+from mozilla.prettyprinters import pretty_printer
+
+# Forget any printers from previous loads of this module.
+mozilla.prettyprinters.clear_module_printers(__name__)
+
+# Summary of the JS::Value type:
+#
+# JS::Value is a 64-bit discriminated union, with JSString*, JSObject*, IEEE
+# 64-bit floating-point, and 32-bit integer branches (and a few others).
+# JS::Value is 64 bits long on all architectures.
+#
+# The ECMAScript standard specifies that ECMAScript numbers are IEEE 64-bit
+# floating-point values. A JS::Value can represent any JavaScript number
+# value directly, without referring to additional storage, or represent an
+# object, string, or other ECMAScript value, and remember which type it is.
+# This may seem surprising: how can a 64-bit type hold all the 64-bit IEEE
+# values, and still distinguish them from objects, strings, and so on,
+# which have 64-bit addresses?
+#
+# This is possible for two reasons:
+#
+# - First, ECMAScript implementations aren't required to distinguish all
+#   the values the IEEE 64-bit format can represent. The IEEE format
+#   specifies many bitstrings representing NaN values, while ECMAScript
+#   requires only a single NaN value. This means we can use one IEEE NaN to
+#   represent ECMAScript's NaN, and use all the other IEEE NaNs to
+#   represent the other ECMAScript values.
+#
+#   (IEEE says that any floating-point value whose 11-bit exponent field is
+#   0x7ff (all ones) and whose 52-bit fraction field is non-zero is a NaN.
+#   So as long as we ensure the fraction field is non-zero, and save a NaN
+#   for ECMAScript, we have 2^52 values to play with.)
+#
+# - Second, on the only 64-bit architecture we support, x86_64, only the
+#   lower 48 bits of an address are significant. The upper sixteen bits are
+#   required to be the sign-extension of bit 48. Furthermore, user code
+#   always runs in "positive addresses": those in which bit 48 is zero. So
+#   we only actually need 47 bits to store all possible object or string
+#   addresses, even on 64-bit platforms.
+#
+# With a 52-bit fraction field, and 47 bits needed for the 'payload', we
+# have up to five bits left to store a 'tag' value, to indicate which
+# branch of our discriminated union is live.
+#
+# Thus, we define JS::Value representations in terms of the IEEE 64-bit
+# floating-point format:
+#
+# - Any bitstring that IEEE calls a number or an infinity represents that
+#   ECMAScript number.
+#
+# - Any bitstring that IEEE calls a NaN represents either an ECMAScript NaN
+#   or a non-number ECMAScript value, as determined by a tag field stored
+#   towards the most significant end of the fraction field (exactly where
+#   depends on the address size). If the tag field indicates that this
+#   JS::Value is an object, the fraction field's least significant end
+#   holds the address of a JSObject; if a string, the address of a
+#   JSString; and so on.
+#
+# On x86_64 only the lower 48 bits of an address are significant, and only
+# those values whose top bit is zero are used for user-space addresses. Thus
+# x86_64 addresses are effectively 47 bits long and fit nicely in the available
+# portion of the fraction field.
+#
+# See Value.h for full details.
+
+
+class Box(object):
+    def __init__(self, asBits, jtc):
+        self.asBits = asBits
+        self.jtc = jtc
+        # Value::asBits is uint64_t, but somehow the sign bit can be botched
+        # here, even though Python integers are arbitrary precision.
+        if self.asBits < 0:
+            self.asBits = self.asBits + (1 << 64)
+
+    # Return this value's type tag.
+    def tag(self):
+        raise NotImplementedError
+
+    # Return this value as a 32-bit integer, double, or address.
+    def as_uint32(self):
+        raise NotImplementedError
+
+    def as_double(self):
+        packed = struct.pack("q", self.asBits)
+        (unpacked,) = struct.unpack("d", packed)
+        return unpacked
+
+    def as_address(self):
+        raise NotImplementedError
+
+
+class Punbox(Box):
+    # Packed non-number boxing --- the format used on x86_64. It would be nice to
+    # simply call Value::toInt32, etc. here, but the debugger is likely to see many
+    # Values, and doing several inferior calls for each one seems like a bad idea.
+
+    FULL_WIDTH = 64
+    TAG_SHIFT = 47
+    PAYLOAD_MASK = (1 << TAG_SHIFT) - 1
+    TAG_MASK = (1 << (FULL_WIDTH - TAG_SHIFT)) - 1
+    TAG_MAX_DOUBLE = 0x1FFF0
+    TAG_TYPE_MASK = 0x0000F
+
+    def tag(self):
+        tag = self.asBits >> Punbox.TAG_SHIFT
+        if tag <= Punbox.TAG_MAX_DOUBLE:
+            return self.jtc.DOUBLE
+        else:
+            return tag & Punbox.TAG_TYPE_MASK
+
+    def as_uint32(self):
+        return int(self.asBits & ((1 << 32) - 1))
+
+    def as_address(self):
+        return gdb.Value(self.asBits & Punbox.PAYLOAD_MASK)
+
+
+class Nunbox(Box):
+    TAG_SHIFT = 32
+    TAG_CLEAR = 0xFFFF0000
+    PAYLOAD_MASK = 0xFFFFFFFF
+    TAG_TYPE_MASK = 0x0000000F
+
+    def tag(self):
+        tag = self.asBits >> Nunbox.TAG_SHIFT
+        if tag < Nunbox.TAG_CLEAR:
+            return self.jtc.DOUBLE
+        return tag & Nunbox.TAG_TYPE_MASK
+
+    def as_uint32(self):
+        return int(self.asBits & Nunbox.PAYLOAD_MASK)
+
+    def as_address(self):
+        return gdb.Value(self.asBits & Nunbox.PAYLOAD_MASK)
+
+
+class JSValueTypeCache(object):
+    # Cache information about the Value type for this objfile.
+
+    def __init__(self, cache):
+        # Capture the tag values.
+        d = gdb.types.make_enum_dict(gdb.lookup_type("JSValueType"))
+
+        # The enum keys are prefixed when building with some compilers (clang at
+        # a minimum), so use a helper function to handle either key format.
+        def get(key):
+            val = d.get(key)
+            if val is not None:
+                return val
+            return d["JSValueType::" + key]
+
+        self.DOUBLE = get("JSVAL_TYPE_DOUBLE")
+        self.INT32 = get("JSVAL_TYPE_INT32")
+        self.UNDEFINED = get("JSVAL_TYPE_UNDEFINED")
+        self.BOOLEAN = get("JSVAL_TYPE_BOOLEAN")
+        self.MAGIC = get("JSVAL_TYPE_MAGIC")
+        self.STRING = get("JSVAL_TYPE_STRING")
+        self.SYMBOL = get("JSVAL_TYPE_SYMBOL")
+        self.BIGINT = get("JSVAL_TYPE_BIGINT")
+        self.NULL = get("JSVAL_TYPE_NULL")
+        self.OBJECT = get("JSVAL_TYPE_OBJECT")
+
+        # Let self.magic_names be an array whose i'th element is the name of
+        # the i'th magic value.
+        d = gdb.types.make_enum_dict(gdb.lookup_type("JSWhyMagic"))
+        self.magic_names = list(range(max(d.values()) + 1))
+        for (k, v) in d.items():
+            self.magic_names[v] = k
+
+        # Choose an unboxing scheme for this architecture.
+        self.boxer = Punbox if cache.void_ptr_t.sizeof == 8 else Nunbox
+
+
+@pretty_printer("JS::Value")
+class JSValue(object):
+    def __init__(self, value, cache):
+        # Save the generic typecache, and create our own, if we haven't already.
+        self.cache = cache
+        if not cache.mod_JS_Value:
+            cache.mod_JS_Value = JSValueTypeCache(cache)
+        self.jtc = cache.mod_JS_Value
+
+        self.value = value
+        self.box = self.jtc.boxer(value["asBits_"], self.jtc)
+
+    def to_string(self):
+        tag = self.box.tag()
+
+        if tag == self.jtc.UNDEFINED:
+            return "$JS::UndefinedValue()"
+        if tag == self.jtc.NULL:
+            return "$JS::NullValue()"
+        if tag == self.jtc.BOOLEAN:
+            return "$JS::BooleanValue(%s)" % str(self.box.as_uint32() != 0).lower()
+        if tag == self.jtc.MAGIC:
+            value = self.box.as_uint32()
+            if 0 <= value and value < len(self.jtc.magic_names):
+                return "$JS::MagicValue(%s)" % (self.jtc.magic_names[value],)
+            else:
+                return "$JS::MagicValue(%d)" % (value,)
+
+        if tag == self.jtc.INT32:
+            value = self.box.as_uint32()
+            signbit = 1 << 31
+            value = (value ^ signbit) - signbit
+            return "$JS::Int32Value(%s)" % value
+
+        if tag == self.jtc.DOUBLE:
+            return "$JS::DoubleValue(%s)" % self.box.as_double()
+
+        if tag == self.jtc.STRING:
+            value = self.box.as_address().cast(self.cache.JSString_ptr_t)
+        elif tag == self.jtc.OBJECT:
+            value = self.box.as_address().cast(self.cache.JSObject_ptr_t)
+        elif tag == self.jtc.SYMBOL:
+            value = self.box.as_address().cast(self.cache.JSSymbol_ptr_t)
+        elif tag == self.jtc.BIGINT:
+            return "$JS::BigIntValue()"
+        else:
+            value = "unrecognized!"
+        return "$JS::Value(%s)" % (value,)