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[lld][ELF] Support for zero flag section groups

Authored by phosek on Feb 12 2021, 2:31 PM.



This change introduces support for zero flag ELF section groups to lld.
lld already supports COMDAT sections, which in ELF are a special type of
ELF section groups. These are generally useful to enable linker GC where
you want a group of sections to always travel together, that is to be
either retained or discarded as a whole, but without the COMDAT
semantics. Other ELF linkers already support zero flag ELF section
groups and this change helps us reach feature parity.

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Event Timeline

phosek created this revision.Feb 12 2021, 2:31 PM
phosek requested review of this revision.Feb 12 2021, 2:31 PM
Herald added a project: Restricted Project. · View Herald TranscriptFeb 12 2021, 2:31 PM
MaskRay added inline comments.Feb 13 2021, 3:01 PM
11 ↗(On Diff #323482)

This tests a real world use case, .debug_types which has the GRP_COMDAT flag.

You can add another section to gc-sections-group.s

phosek updated this revision to Diff 323578.Feb 13 2021, 3:41 PM
phosek marked an inline comment as done.
phosek updated this revision to Diff 323579.Feb 13 2021, 3:43 PM
phosek updated this revision to Diff 323580.Feb 13 2021, 4:02 PM
MaskRay accepted this revision.Feb 13 2021, 4:57 PM


This revision is now accepted and ready to land.Feb 13 2021, 4:57 PM
jhenderson accepted this revision.Feb 15 2021, 2:08 AM

Looks good, with a couple of small comments.


I wonder whether isNew is a bit misnamed nowadays. Perhaps it should be renamed to keepGroup or something like that. Waht do you think?

phosek updated this revision to Diff 324054.Feb 16 2021, 11:01 AM
phosek marked 2 inline comments as done.
phosek added inline comments.

That makes sense, I've renamed this to keepGroup.

This revision was landed with ongoing or failed builds.Feb 16 2021, 2:34 PM
This revision was automatically updated to reflect the committed changes.