This patch adds two macros to declare per-type allocators:
- JS_DECLARE_ALLOCATOR(TypeName)
- JS_DEFINE_ALLOCATOR(TypeName)
When used, they add a type-specific CellAllocator that the Heap will
delegate allocation requests to.
The result of this is that GC objects of the same type always end up
within the same HeapBlock, drastically reducing the ability to perform
type confusion attacks.
It also improves HeapBlock utilization, since each block now has cells
sized exactly to the type used within that block. (Previously we only
had a handful of block sizes available, and most GC allocations ended
up with a large amount of slack in their tails.)
There is a small performance hit from this, but I'm sure we can make
up for it elsewhere.
Note that the old size-based allocators still exist, and we fall back
to them for any type that doesn't have its own CellAllocator.
Note that as of this commit, there aren't any such throwers, and the
call site in Heap::allocate will drop exceptions on the floor. This
commit only serves to change the declaration of the overrides, make sure
they return an empty value, and to propagate OOM errors frm their base
initialize invocations.
Instead of hardcoding all the property definitions in GlobalObject's
initialize() function, make it the standalone AO it is supposed to be
that can then be used by other global objects that don't inherit from
JS::GlobalObject.
This will later allow global objects not inheriting from the regular
JS::GlobalObject to pull in these functions without having to implement
them from scratch. The primary use case here is, again, a wrapper-less
HTML::Window in LibWeb :^)
Allocating these upfront now allows us to get rid of two hacks:
- The GlobalObject assigning Intrinsics private members after finishing
its initialization
- The GlobalObject defining the parseInt and parseFloat properties of
the NumberConstructor object, as they are supposed to be identical
with the global functions of the same name
Intrinsics, i.e. mostly constructor and prototype objects, but also
things like empty and new object shape now live on a new heap-allocated
JS::Intrinsics object, thus completing the long journey of taking all
the magic away from the global object.
This represents the Realm's [[Intrinsics]] slot in the spec and matches
its existing [[GlobalObject]] / [[GlobalEnv]] slots in terms of
architecture.
In the majority of cases it should now be possibly to fully allocate a
regular object without the global object existing, and in fact that's
what we do now - the realm is allocated before the global object, and
the intrinsics between both :^)
Global object initialization is tightly coupled to realm creation, so
simply pass it to the function instead of relying on the non-standard
'associated realm' concept, which I'd like to remove later.
This works essentially the same way as regular Object::initialize() now.
Additionally this allows us to forward the realm to GlobalObject's
add_constructor() / initialize_constructor() helpers, so they set the
correct realm on the allocated constructor function object.
This is a continuation of the previous three commits.
Now that create() receives the allocating realm, we can simply forward
that to allocate(), which accounts for the majority of these changes.
Additionally, we can get rid of the realm_from_global_object() in one
place, with one more remaining in VM::throw_completion().
No functional changes - we can still very easily get to the global
object via `Realm::global_object()`. This is in preparation of moving
the intrinsics to the realm and no longer having to pass a global
object when allocating any object.
In a few (now, and many more in subsequent commits) places we get a
realm using `GlobalObject::associated_realm()`, this is intended to be
temporary. For example, create() functions will later receive the same
treatment and are passed a realm instead of a global object.
The existing code looks innocently correct, implementing the following
step:
3. If IsCallable(func) is false, set func to the intrinsic function
%Object.prototype.toString%.
as
return ObjectPrototype::to_string(vm, global_object);
However, this misses the fact that the next step calls the function with
the previously ToObject()'d this value (`array`):
4. Return ? Call(func, array).
This doesn't happen in the current implementation, which will use the
unaltered this value from the Array.prototype.toString() call, and make
another, unequal object in %Object.prototype.toString%. Since both that
and Array.prototype.toString() do a Get() call on said object, this
behavior is observable (see newly added test).
Fix this by actually doing what the spec says and calling the fallback
function the regular way.
We were previously manually initializing them instead of just calling
GlobalObject::initialize_constructor, which aside from duplicating code
also meant we didn't set the required name property.
Given we usually call objects Foo{Object,Constructor,Prototype} or
Foo{,Constructor,Prototype}, this name was an odd choice.
The new one matches the spec better, which calls it the "Generator
Prototype Object", so we simply omit the Object suffix as usual as it's
implied.
The old versions were renamed to JS_DECLARE_OLD_NATIVE_FUNCTION and
JS_DEFINE_OLD_NATIVE_FUNCTION, and will be eventually removed once all
native functions were converted to the new format.
This is just another workaround, but it should be much more reliable
than Interpreter::realm(), especially when allocating NativeFunctions
and ECMAScriptFunctionObjects: we're guaranteed to have a GlobalObject
at that point, and it likely was set as the GlobalObject of a Realm and
can lead us back to it. We're however not guaranteed that the VM can
give us an Interpreter, which is why functions in LibWeb can be a bit
crashy at the moment.
We use a WeakPtr<Realm> to properly handle the unlikely case where the
Realm goes away after associating a GlobalObject to it.
We'll always need _something_ of this sort if we want to support
OrdinaryFunctionCreate and CreateBuiltinFunction without the explicit
realm argument while no JS is running, because they want to use the
current Realm Record (always in the first and as fallback in the second
case).
The way that transition avoidance (foo_without_transition) was
implemented led to shapes being unshareable and caused shape explosion
instead, precisely what we were trying to avoid.
This patch removes all the attempts to avoid transitioning shapes, and
instead *adds* transitions when changing an object's prototype.
This makes transitions flow naturally, and as a result we end up with
way fewer shape objects in real-world situations.
When we run out of big problems, we can get back to avoiding transitions
as an optimization, but for now, let's avoid ballooning our processes
with a unique shape for every object.
This is where the spec wants to have it. Requires a couple of hacks as
currently everything that needs a Realm actually has a GlobalObject, so
we need to go via the Interpreter.
We don't need transitions for either of these:
- Adding the 'name' property to a constructor object
- Adding the 'constructor' property to its prototype object
This is a tiny difference and only changes anything for primitives in
strict mode. However this is tested in test262 and can be noticed by
overriding toString of primitive values.
This does now require one to wrap an object in a Value to call invoke
but all code using invoke has been migrated.
Add a JS_ENUMERATE_INTL_OBJECTS macro and use it to generate:
- Forward declarations
- CommonPropertyNames class name members
- Constructor and prototype GlobalObject members, getters, visitors,
and initialize_constructor() calls
Add a JS_ENUMERATE_TEMPORAL_OBJECTS macro and use it to generate:
- Forward declarations
- CommonPropertyNames class name members
- Constructor and prototype GlobalObject members, getters, visitors,
and initialize_constructor() calls
This removes all usages of the non-standard define_property helper
method and replaces all it's usages with the specification required
alternative or with define_direct_property where appropriate.
These represent the outermost scope in the environment record
hierarchy. The spec says they should be a "composite" of two things:
- An ObjectEnvironmentRecord wrapping the global object
- A DeclarativeEnvironmentRecord for other declarations
It's not yet clear to me how this should work, so this patch only
implements the first part, an object record wrapping the global object.
