1530296 - Fix undefined behavior in WebIDL cast

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement)

Description

[Andy Wingo [:wingo]]

This cast would seem to have undefined behavior, which we should fix:

https://searchfox.org/mozilla-central/source/js/src/builtin/DataViewObject.cpp#414-418

Comment 1

[Jeff Walden [:Waldo]]

Attachment: Be more careful about converting int32_t to DataView element type

On second look, I don't think this comment is really right.  Casting out-of-range value to signed isn't UB, it's *implementation-defined*, which isn't necessarily unsafe.

But it's easy enough to make this all be wholly-defined operations -- cast to unsigned type is defined as modulus, WrapToSigned was written carefully to avoid any UB itself -- so we should just do that.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/5ea654f841a4
Be more careful about converting int32_t to DataView element type.  r=froydnj

Comment 3

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/5ea654f841a4