744192 - GC: ensure there are no implicit post barriers in a Vector

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Terrence Cole [:terrence]]

Attachment: v0

If we store an implicitly post barriered type in a vector, we will fall over when the vector relocates our storage.  This patch simply asserts that we do not have any.  We still compile with this and grepping for "Vector<Heap" did not turn up any results, so I think we are in the clear with these.  This assertion will ensure that we stay in the clear going forward.

Comment 1

[Luke Wagner [:luke]]

Comment on attachment 613773 [details] [diff] [review]
v0

Review of attachment 613773 [details] [diff] [review]:
-----------------------------------------------------------------

::: js/public/Vector.h
@@ +284,5 @@
>      Vector &operator=(const Vector &) MOZ_DELETE;
>  
> +    void checkStaticInvarients() {
> +        JS_STATIC_ASSERT(!tl::IsPostBarrieredType<T>::result);
> +    }

I usually make these things 'static'

@@ +534,5 @@
>  #ifdef DEBUG
>    , mReserved(0), entered(false)
>  #endif
> +{
> +    checkStaticInvarients();

I don't think you need to call it to get the static checks.

Comment 2

[Terrence Cole [:terrence]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/a43eb4a2d2fd

With review comments _not_ applied, as per our IRC conversation.

Comment 3

[Terrence Cole [:terrence]]

And backed out in:

https://hg.mozilla.org/integration/mozilla-inbound/rev/4e05bd6470c8

Old and busted gcc says: "error: default template arguments may not be used in function templates".

Comment 4

[Jeff Walden [:Waldo]]

Actually gcc's right about that.  You have to have a pointless <> when calling a templatized function where all the template arguments are defaulted, in C++98.  (C++11 allows you to omit the <> when calling a function using entirely default template arguments.)  Clang should be warning/erroring on the same thing, not sure why it wouldn't be here.

Oh, and it's "invariants", not "invarients".

Comment 5

[Jeff Walden [:Waldo]]

Er, wait, that first paragraph of comment 4 is not actually correct, or at least I'm not sure it is as regards the situation here -- ignore it.

Comment 6

[Terrence Cole [:terrence]]

Attachment: v1: Carrying review forward, since Luke gave me the working solution. :-)

Using tl::StaticAssert works much better, and is cleaner to boot.

Comment 7

[Terrence Cole [:terrence]]

https://tbpl.mozilla.org/?tree=Mozilla-Inbound&rev=380e6f8bd681

Comment 8

[:Ms2ger (he/him; ⌚ UTC+1/+2)]

https://hg.mozilla.org/mozilla-central/rev/380e6f8bd681