[SR-1901] Linker error "hidden symbol" on subclassing Thread

[aciidgh]

Previous ID	SR-1901
Radar	None
Original Reporter	@aciidb0mb3r
Type	Bug
Status	Resolved
Resolution	Done

Environment

Linux

Additional Detail from JIRA

Votes	1
Component/s	Foundation, XCTest
Labels	Bug
Assignee	@eeckstein
Priority	Medium

md5: b317e664abb519336896529a6617e8d9

relates to:

• SR-1129 Linker step fails when subclassing a class with a 'public private(set) var'
• SR-2170 Linux Linker error when deriving a class from NSURL

Issue Description:

This code produces a linker error on Linux:

import class Foundation.Thread

class Thread: Foundation.Thread {
}

$ swiftc Thread.swift
/usr/bin/ld.gold: error: hidden symbol '_TFC10Foundation6Threadg5_mainFT_T_' is not defined locally
/usr/bin/ld.gold: error: hidden symbol '_TFC10Foundation6Threads5_mainFT_T_' is not defined locally
/usr/bin/ld.gold: error: hidden symbol '_TFC10Foundation6Threadm5_mainFT_T_' is not defined locally
/usr/bin/ld.gold: error: hidden symbol '_TFC10Foundation6ThreadgP33_513815EE0AA0753AFF631398622CF9397_threadSu' is not defined locally
/usr/bin/ld.gold: error: hidden symbol '_TFC10Foundation6ThreadsP33_513815EE0AA0753AFF631398622CF9397_threadSu' is not defined locally
/usr/bin/ld.gold: error: hidden symbol '_TFC10Foundation6ThreadmP33_513815EE0AA0753AFF631398622CF9397_threadSu' is not defined locally
/usr/bin/ld.gold: error: hidden symbol '_TFC10Foundation6Threadg5_attrVSC14pthread_attr_t' is not defined locally
/usr/bin/ld.gold: error: hidden symbol '_TFC10Foundation6Threads5_attrVSC14pthread_attr_t' is not defined locally
/usr/bin/ld.gold: error: hidden symbol '_TFC10Foundation6Threadm5_attrVSC14pthread_attr_t' is not defined locally
/usr/bin/ld.gold: error: hidden symbol '_TFC10Foundation6Threadg7_statusOS_15_NSThreadStatus' is not defined locally
/usr/bin/ld.gold: error: hidden symbol '_TFC10Foundation6Threads7_statusOS_15_NSThreadStatus' is not defined locally
/usr/bin/ld.gold: error: hidden symbol '_TFC10Foundation6Threadm7_statusOS_15_NSThreadStatus' is not defined locally
/usr/bin/ld.gold: error: hidden symbol '_TFC10Foundation6Threadg10_cancelledSb' is not defined locally
/usr/bin/ld.gold: error: hidden symbol '_TFC10Foundation6Threads10_cancelledSb' is not defined locally
/usr/bin/ld.gold: error: hidden symbol '_TFC10Foundation6Threadm10_cancelledSb' is not defined locally
clang: error: linker command failed with exit code 1 (use -v to see invocation)
<unknown>:0: error: link command failed with exit code 1 (use -v to see invocation)

However no error if ran as a script:
$ swift Thread.swift
<no error>

[ddunbar]

I'm not sure what is happening here – I think this could be a compiler issue or an issue with how Foundation is building itself.

/cc @jckarter @rjmccall

[modocache]

Thanks for linking https://bugs.swift.org/browse/SR-1129 to this report. I'd love to see this issue resolved – swift-corelibs-xctest is unable to deliver on its promise of API parity with Apple XCTest due to this.

Be sure to check out swiftlang/swift#2039 for a failing test demonstrating the problem.

[rjmccall]

Looks like some code is getting the SIL linkage wrong for the getters and setters in the v-table.

[modocache]

Another example of this affecting corelibs API: #651

[jckarter]

@rjmccall At least some of those symbols include private discriminators. It looks like we try to directly reference inherited private/internal vtable entries from the parent class in the subclass's vtable, which is of course totally unworkable. Foundation might be able to work around this by making the affected properties final, if possible.

[modocache]

Thanks for the workaround suggestion! I tried using it for XCTest here (still waiting on CI results): swiftlang/swift-corelibs-xctest#173

The workaround doesn't cover all cases, unfortunately. For example, XCTest has properties that have public getters, private setters, and (for the sake of API parity of Objective-C XCTest) can be overridden: https://github.com/apple/swift-corelibs-xctest/blob/3b6c476eccee86b92f215257147a5f8d0aed3ba4/Sources/XCTest/Public/XCAbstractTest.swift#L37-L42. Since these are open, they cannot also be marked final.

[eeckstein]

I'm working on it.

[eeckstein]

fixed in fd61338444ac42d8715fd9e637b238e035f17f8d

[modocache]

Awesome Submitting a fix for the public symbols in XCTest now.

[parkera]

Thanks Erik!

[swift-ci]

Comment by David Grove (JIRA)

Hi Erik

Can we get this fix into the Swift3 branch as well? I just tried against swift-3.0.1-PREVIEW-3-ubuntu16.04 and the bug is still there.

[eeckstein]

I cherry picked it into swift 3 a few days ago, so it should be on the way.
(Sorry for not doing it earlier)

[swift-ci]

Comment by David Grove (JIRA)

Great, thanks! Sorry for not looking more closely at the Swift3 branch; missed that it was done already.