libcxxrt: add padding in __cxa_allocate_* to fix alignment
ClosedPublic
Actions

Authored by emaste on Jul 21 2016, 2:31 PM.

Details

Reviewers

dim
theraven
ed

Commits

rS316356: Synchronize libcxxrt in stable/9 with stable/{10,11} and head.
rS315965: Synchronize libcxxrt in stable/10 with stable/11.
rS303157: libcxxrt: add padding in __cxa_allocate_* to fix alignment

Summary

Prior to the addition of the referenceCount in __cxa_exception the unwindHeader was at offset 0x50, and it requires 16-byte alignment. Add padding in the same location that it will appear in libstdc++.

Diff Detail

Repository

rS FreeBSD src repository - subversion

Lint

Lint Not Applicable

Unit

Tests Not Applicable

Event Timeline

emaste updated this revision to Diff 18631.Jul 21 2016, 2:31 PM

emaste retitled this revision from to libcxxrt: add padding to __cxa_exception to fix alignment.

emaste updated this object.

emaste edited the test plan for this revision. (Show Details)

emaste added reviewers: dim, theraven, ed.

emaste added a subscriber: gjb.

Here's a libstdc++ bug for a nearly identical issue issue: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=38732
See specifically comment 13: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=38732#c13

Avoid changing the __cxa_exception ABI in 11.

The addition of the referenceCount to __cxa_allocate_exception put the unwindHeader at offset 0x58, but it requires 16-byte alignment. In order to avoid changing the broken __cxa_exception ABI (and thus breaking its consumers), add explicit padding in the allocation routins (and account for it when freeing).

emaste added inline comments.Jul 21 2016, 5:43 PM

contrib/libcxxrt/exception.cc
576–582 ↗	(On Diff #18633)	Should this be `//` comments instead?

LGTM. This looks like the least intrusive solution.

contrib/libcxxrt/exception.cc
576–582 ↗	(On Diff #18633)	Not necessary, for instance the block below it uses `/**`, which appears to be used for longer comments (though not very consistently).