1020414 - gcc -Wuninitialized warning (uninitialized memory copy) in Nullable's copy ctor when copying default constructed Nullable

Status: RESOLVED DUPLICATE of bug 1025173

(Core :: DOM: Core & HTML, defect)

Description

[Chris Peterson [:cpeterson]]

I see the following gcc -Wuninitialized warning about an uninitialized memory copy from this code:

https://hg.mozilla.org/mozilla-central/annotate/c7fdd7e755cd/dom/quota/QuotaManager.cpp#l2812

Here is a simplified example:

> Nullable a;
> Nullable b(a); // b's copy ctor copying a's uninitialized mValue


In file included from ../../dist/include/nsIDOMEventTarget.h:18:0,
                 from ../../dist/include/mozilla/dom/EventTarget.h:9,
                 from ../../dist/include/nsPIDOMWindow.h:16,
                 from /builds/slave/try-l64-d-00000000000000000000/build/dom/quota/CheckQuotaHelper.cpp:15,
                 from /builds/slave/try-l64-d-00000000000000000000/build/obj-firefox/dom/quota/Unified_cpp_dom_quota0.cpp:2:
../../dist/include/mozilla/dom/Nullable.h: In member function 'nsresult mozilla::dom::quota::QuotaManager::ClearStoragesForApp(uint32_t, bool)':
../../dist/include/mozilla/dom/Nullable.h:44:27: warning: '*((void*)& persistenceType +4)' may be used uninitialized in this function [-Wuninitialized]
In file included from /builds/slave/try-l64-d-00000000000000000000/build/obj-firefox/dom/quota/Unified_cpp_dom_quota0.cpp:28:0:
/builds/slave/try-l64-d-00000000000000000000/build/dom/quota/QuotaManager.cpp:2808:29: note: '*((void*)& persistenceType +4)' was declared here