907489 - PresShell::HandleEvent() never initializes its "flags" variable

Status: RESOLVED FIXED

(Core :: Layout, defect)

Description

[Daniel Holbert [:dholbert]]

Newish build warning, with GCC 4.8 on Linux:
{
layout/base/nsPresShell.cpp:6185:48: warning: 'flags' may be used uninitialized in this function [-Wmaybe-uninitialized]
}

This is from this change:
> +      uint32_t flags;
>        if (aEvent->message == NS_TOUCH_START) {
> +        flags |= INPUT_IGNORE_ROOT_SCROLL_FRAME;
http://hg.mozilla.org/mozilla-central/rev/8a68e032ca51#l1.12

from bug 901962 , which kats landed last week.

And the warning is very right, AFAICT -- we're declaring "flags", uninitialized, and then we start orring in some bits.

Presumably we should be declaring it as "uint32_t flags = 0;" right?

Comment 1

[Bill McCloskey [inactive unless it's an emergency] (:billm)]

Attachment: uninit-flags

Oddly, this causes scrollbars not to work in e10s.

Comment 2

[Bill McCloskey [inactive unless it's an emergency] (:billm)]

https://hg.mozilla.org/integration/mozilla-inbound/rev/ce293f97be57

Comment 3

[Ed Morley [:emorley]]

https://hg.mozilla.org/mozilla-central/rev/ce293f97be57

Comment 4

[Kartikaya Gupta (email:[e-mail])]

Good catch, thanks for the fix!

Comment 5

[Aaron Train [:aaronmt]]

Uplift?

Comment 6

[Kartikaya Gupta (email:[e-mail])]

Comment on attachment 793241 [details] [diff] [review]
uninit-flags

[Approval Request Comment]
Bug caused by (feature/regressing bug #): bug 901962
User impact if declined: possibly random behaviour from an uninitialized variable
Testing completed (on m-c, etc.): on m-c
Risk to taking this patch (and alternatives if risky): very low risk
String or IDL/UUID changes made by this patch: none

Comment 7

[Alex Keybl [:akeybl]]

Comment on attachment 793241 [details] [diff] [review]
uninit-flags

We didn't end up approving bug 901962