700501 - [ObjShrink] "Assertion failure: [infer failure] Missing type for arg 0: <0xf6b0aaa0>," or "Assertion failure: [infer failure] Missing type for arg 0: [0xf6c001c0],"

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Gary Kwong [:gkw] [:nth10sd] (NOT official MoCo now)]

Function.prototype.__proto__["p"] = 3
c = [].__proto__
c[5] = 3
Namespace.prototype.__proto__[4] = function() {}
gc()
Function("\
    {\
    function f(d) {}\
    for each(let z in[0]) {\
        f(z)\
    }\
    }\
")()

asserts js debug shell on JM changeset 1210706b4576 with -m, -a and -n at Assertion failure: [infer failure] Missing type for arg 0: <0xf6b0aaa0>,

This was found using a combination of jsfunfuzz and jandem's method fuzzer.

Comment 1

[Gary Kwong [:gkw] [:nth10sd] (NOT official MoCo now)]

This may be related:

gc()
Function("\
    {\
    function g(f){}\
    for each(let w in[0,0,0,[]]) {\
        g(w)\
    }\
    }\
")()

Assertion failure: [infer failure] Missing type for arg 0: [0xf6c001c0],

Comment 2

[Brian Hackett [Laid off!]]

Attachment: patch

The default 'new' types of certain objects (Object.prototype, Array.prototype, Function.prototype) are required in several places to have unknown property types.  This broke with the object newType changes --- the object's new type is no longer a strong reference, and if it goes away and is recreated then the recreated type did not have unknown property types.  The fix adds a bit to the flags in the prototype's base shape to indicate whether default 'new' types created off the object need unknown properties.

https://hg.mozilla.org/projects/jaegermonkey/rev/493d52c0a104

Comment 7

[Luke Wagner [:luke]]

Comment on attachment 573059 [details] [diff] [review]
patch

Review of attachment 573059 [details] [diff] [review]:
-----------------------------------------------------------------

::: js/src/jsinfer.cpp
@@ +5740,5 @@
> +    JSCompartment::NewTypeObjectSet &table = compartment()->newTypeObjects;
> +    if (table.initialized()) {
> +        JSCompartment::NewTypeObjectSet::Ptr p = table.lookup(this);
> +        if (p)
> +            MarkTypeObjectUnknownProperties(cx, *p);

if (JSCompartment::NewTypeObjectSet::Ptr p = ...)

::: js/src/jsobj.h
@@ +833,5 @@
> +    /*
> +     * Mark an object as requiring its default 'new' type to have unknown
> +     * properties. This is set for a few builtins like Object.prototype and
> +     * Array.prototype; several places in the VM require that the default
> +     * type for these objects have unknown contents.

Could you explain in more detail why some places in the VM requires this?  If its a dirty hack, you could point to the dependent sites which should have explanatory comments; if its a general invariant, you could describe it.

Comment 8

[Christian Holler (:decoder)]

A testcase for this bug was automatically identified at js/src/jit-test/tests/basic/bug700501.js.