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[SR-6718] Linux Interoperability: Eliminate items in class metadata layout that aren't relevant to non-objc builds #49267

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AnnaZaks mannequin opened this issue Jan 8, 2018 · 4 comments
Closed

[SR-6718] Linux Interoperability: Eliminate items in class metadata layout that aren't relevant to non-objc builds #49267

AnnaZaks mannequin opened this issue Jan 8, 2018 · 4 comments
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself Linux Platform: Linux runtime The Swift Runtime

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@AnnaZaks
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AnnaZaks mannequin commented Jan 8, 2018

Previous ID SR-6718
Radar rdar://problem/18801263
Original Reporter @AnnaZaks
Type Bug
Status Resolved
Resolution Done
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, Linux, Runtime
Assignee None
Priority Medium

md5: 1801085f2cc5dfb398494cbf214ff76d

Issue Description:

There are various places in the metadata generation where NULL values are being injected simply because there’s some objective-c related field that isn’t important on a non-objc platform. We should remove these and make sure that things still work. (Note that the debugger wants to preserve some sort of magic number that can be used to identify classes. On ObjC platforms the debugger uses the Swift class's ObjC data to do that.)
@belkadan
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Reminded of this again today. I don't think it would be too difficult, so maybe a good task to assign to someone who's already familiar with the compiler a bit and wants to dive into IRGen and the runtime?

As for a "magic number to identify classes", the value witness table for every class is the same (since it's "just" for native-object references), so we can probably use that: $sBoWV

@belkadan
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belkadan commented Oct 1, 2020

Apparently @davezarzycki got around to this in #31811 so it'll make it into 5.4 (or 6, whatever's next).

@belkadan
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belkadan commented Oct 1, 2020

Tagging @mikeash to make sure the Radar gets closed too.

@mikeash
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mikeash commented Oct 1, 2020

Thanks Jordan, you have pleased the Lords of Radar.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself Linux Platform: Linux runtime The Swift Runtime
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@mikeash @belkadan