898916 - Statically allocated classinfo objects are not properly aligned

Status: RESOLVED FIXED

(Core :: XPCOM, defect)

Description

[Mike Hommey [:glandium]]

Changeset 2ad039920033 added k${class}ClassInfoDataPlace buffers that are used as static allocation location for GenericClassInfo, but no effort is made to make the alignment correct. This causes unaligned read accesses on e.g. arm. I'm actually surprised this doesn't break our armv6 builds. It does, however, break Debian armel.

Comment 1

[Mike Hommey [:glandium]]

Attachment: Properly align statically allocated classinfo objects

Comment 2

[Mike Hommey [:glandium]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/7506c6ee2e8b

Comment 3

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/7506c6ee2e8b

Comment 4

[Mike Hommey [:glandium]]

Comment on attachment 782332 [details] [diff] [review]
Properly align statically allocated classinfo objects

[Approval Request Comment]
User impact if declined: Linux ARM builds don't work, and I suspect this also affects sparc and other architectures that don't like misaligned word accesses. It would be nice if this could land in the next ESR for linux distros.
Testing completed (on m-c, etc.): Landed on m-c a couple days ago.
Risk to taking this patch (and alternatives if risky): In practice, the patch only changes the alignment of a data buffer in the resulting binary. Risk of this breaking anything is really low.
String or IDL/UUID changes made by this patch: None.

Comment 5

[Lukas Blakk [:lsblakk] use ?needinfo]

Comment on attachment 782332 [details] [diff] [review]
Properly align statically allocated classinfo objects

low risk and useful for support of linux in the next ESR version, approving.

Comment 6

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/releases/mozilla-aurora/rev/4a2ea5f02321

Comment 7

[u279076]

Assuming no QA needed here. Please remove [qa-] from the whiteboard and add the verifyme keyword if this needs QA.