1430729 - '*<unknown>.mozilla::StaticAutoPtr<mozilla::SandboxReporter>::mRawPtr' is used uninitialized in this function [-Werror=uninitialized]

Status: RESOLVED FIXED

(Core :: XPCOM, defect)

Description

[Sylvestre Ledru [:Sylvestre]]

with gcc 8-20180110-1
 In file included from /root/firefox-gcc-last/security/sandbox/linux/reporter/SandboxReporter.h:13,
                  from /root/firefox-gcc-last/security/sandbox/linux/reporter/SandboxReporter.cpp:7:
 /root/firefox-gcc-last/obj-x86_64-pc-linux-gnu/dist/include/mozilla/StaticPtr.h: In constructor 'mozilla::StaticAutoPtr<T>::StaticAutoPtr() [with T = mozilla::SandboxReporter]':
 /root/firefox-gcc-last/obj-x86_64-pc-linux-gnu/dist/include/mozilla/StaticPtr.h:48:17: error: '*<unknown>.mozilla::StaticAutoPtr<mozilla::SandboxReporter>::mRawPtr' is used uninitialized in this function [-Werror=uninitialized]
      MOZ_ASSERT(!mRawPtr);
                  ^~~~~~~
 cc1plus: all warnings being treated as errors

Not sure if this is a bug in the compiler false positive or not.

Comment 1

[James Cheng[:JamesCheng]]

I think we intended not to assign the value for

https://searchfox.org/mozilla-central/rev/41925c0b6c6d58578690121de439d2a8d3d690f3/xpcom/base/StaticPtr.h#48

we assume client should use this object as a global object that means it will be located in BSS section with auto zero initialization.

How could we work around for this warning?

Comment 2

[Nathan Froyd [:froydnj]]

Comment 1 is correct; mRawPtr will always be zero-initialized by the runtime system.  But the compiler can't know that we're always going to use these objects at file scope, so it complains.

#pragma GCC warning disable seems like a reasonable workaround.  Want to try that, Sylvestre?

Comment 3

[Sylvestre Ledru [:Sylvestre]]

Attachment: Bug 1430729 - Ignore an incorrect warning with gcc (-Wuninitialized)

Review commit: https://reviewboard.mozilla.org/r/213182/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/213182/

Comment 4

[Sylvestre Ledru [:Sylvestre]]

Is that what you are expecting? Thanks!

Comment 5

[Nathan Froyd [:froydnj]]

Comment on attachment 8942913 [details]
Bug 1430729 - Ignore an incorrect warning with gcc (-Wuninitialized)

https://reviewboard.mozilla.org/r/213182/#review218858

Thank you!

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/55b7690ea8c5
Ignore an incorrect warning with gcc (-Wuninitialized) r=froydnj

Comment 7

[Andreea Pavel [:apavel]]

Backed out for build bustage z:\build\build\src\obj-firefox\dist\include\mozilla/StaticPtr.h(107): error C2220 on a CLOSED TREE

Push that cause the bustages: https://treeherder.mozilla.org/#/jobs?repo=autoland&revision=55b7690ea8c554e12d11ea015c90a0e2bd115389

Failure log: https://treeherder.mozilla.org/logviewer.html#?job_id=156599549&repo=autoland&lineNumber=7094

Backout: https://hg.mozilla.org/integration/autoland/rev/b2588a5584c200b9dac8a6a0b0500f043cd335fe

Comment 8

[Sylvestre Ledru [:Sylvestre]]

Comment on attachment 8942913 [details]
Bug 1430729 - Ignore an incorrect warning with gcc (-Wuninitialized)

Review request updated; see interdiff: https://reviewboard.mozilla.org/r/213182/diff/1-2/

Comment 9

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/263b74db7a7c
Ignore an incorrect warning with gcc (-Wuninitialized) r=froydnj

Comment 10

[Sylvestre Ledru [:Sylvestre]]

According to the autoland CI, we are much better now!

Comment 11

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/263b74db7a7c