[swift-corelibs-dev] Encountering "Constant strings cannot be deallocated" in Linux foundation

Fri Dec 1 16:32:16 CST 2017

This isn’t it, because we always call through to swift_release in CFRelease on Linux, because the CFString is a swift type under the hood.

We may be able to change this to check for a CF specific hack of some kind, but in the meantime adding the retain works.

PR here:

https://github.com/apple/swift-corelibs-foundation/pull/1351

- Tony

> On Nov 29, 2017, at 8:31 PM, Philippe Hausler <phausler at apple.com> wrote:
> 
> I think that perhaps we have a problem with the retain count flags in the definition of CFSTR. Previously the pinned reference would prevent the deallocation. This may have gotten clobbered with the latest CF import.
> 
> Sent from my iPhone
> 
> On Nov 29, 2017, at 7:55 PM, Brandon Williams via swift-corelibs-dev <swift-corelibs-dev at swift.org <mailto:swift-corelibs-dev at swift.org>> wrote:
> 
>> Hey Tony,
>> 
>> We were able to fix our crashes by avoiding our uses of `URLQueryItem`s. In one place I had to completely remove the use of `URLQueryItem`:
>> 
>> https://github.com/pointfreeco/swift-web/pull/79/files#diff-293b73a926ba418bd9511ef735fc947cL147 <https://github.com/pointfreeco/swift-web/pull/79/files#diff-293b73a926ba418bd9511ef735fc947cL147>
>> 
>> And in another my colleague Stephen Celis discovered that duplicate keys in a query string can cause this to crash:
>> 
>> https://github.com/pointfreeco/swift-web/pull/80 <https://github.com/pointfreeco/swift-web/pull/80>
>> 
>> He was able to come up with a minimal test case to demonstrate this:
>> 
>> https://github.com/pointfreeco/swift-web/commit/cfa9b519a829f1c1627620521326f0877c2d023a <https://github.com/pointfreeco/swift-web/commit/cfa9b519a829f1c1627620521326f0877c2d023a>
>> 
>> And you can see the failure in this Travis CI report:
>> 
>> https://travis-ci.org/pointfreeco/swift-web/builds/309316418 <https://travis-ci.org/pointfreeco/swift-web/builds/309316418?utm_source=email&utm_medium=notification>
>> 
>> At the bottom you’ll find:
>> 
>> ```fatal error: Constant strings cannot be deallocated: file Foundation/NSCFString.swift, line 118```
>> 
>> So definitely seems to be in that area!
>> 
>> Now, as far as rebuilding swift-corelibs-foundation, I’m down to try but I dont really know much about how to do that. With some instructions I could give it a shot.
>> 
>> Thanks for the help!
>> 
>> 
>> 
>> 
>> On Wed, Nov 29, 2017 at 5:59 PM Tony Parker <anthony.parker at apple.com <mailto:anthony.parker at apple.com>> wrote:
>> I see a couple of places that are suspicious there:
>> 
>> Description:
>> 
>> https://github.com/apple/swift-corelibs-foundation/blob/master/CoreFoundation/URL.subproj/CFURLComponents.c#L66 <https://github.com/apple/swift-corelibs-foundation/blob/master/CoreFoundation/URL.subproj/CFURLComponents.c#L66>
>> 
>> And the nameString / valueString constants in the copy query items function:
>> 
>> https://github.com/apple/swift-corelibs-foundation/blob/master/CoreFoundation/URL.subproj/CFURLComponents.c#L1057 <https://github.com/apple/swift-corelibs-foundation/blob/master/CoreFoundation/URL.subproj/CFURLComponents.c#L1057>
>> https://github.com/apple/swift-corelibs-foundation/blob/master/CoreFoundation/URL.subproj/CFURLComponents.c#L1079 <https://github.com/apple/swift-corelibs-foundation/blob/master/CoreFoundation/URL.subproj/CFURLComponents.c#L1079>
>> https://github.com/apple/swift-corelibs-foundation/blob/master/CoreFoundation/URL.subproj/CFURLComponents.c#L1104 <https://github.com/apple/swift-corelibs-foundation/blob/master/CoreFoundation/URL.subproj/CFURLComponents.c#L1104>
>> https://github.com/apple/swift-corelibs-foundation/blob/master/CoreFoundation/URL.subproj/CFURLComponents.c#L1134 <https://github.com/apple/swift-corelibs-foundation/blob/master/CoreFoundation/URL.subproj/CFURLComponents.c#L1134>
>> https://github.com/apple/swift-corelibs-foundation/blob/master/CoreFoundation/URL.subproj/CFURLComponents.c#L1158 <https://github.com/apple/swift-corelibs-foundation/blob/master/CoreFoundation/URL.subproj/CFURLComponents.c#L1158>
>> 
>> Do you have the ability to re-build swift-corelibs-foundation and run a test? I suspect if you replace those with CFRetain(CFSTR(…)) then it will fix your crash.
>> 
>> - Tony
>> 
>> 
>>> On Nov 29, 2017, at 2:06 PM, Brandon Williams <mbw234 at gmail.com <mailto:mbw234 at gmail.com>> wrote:
>>> 
>>> Thanks for the info!
>>> 
>>> FWIW, most of the places I have encountered this so far have made use of `URLComponents`, and have even been able to eliminate the crash by getting rid of that code in a few places. The other JIRA bug on this topic also mentions URLComponents in their repro case. Seems to be the culprit.
>>> 
>>> Also worth noting that in the above cases dealing with URLComponents the crash only happens in DEBUG compilations, not RELEASE.
>>> 
>>> However, I do have another one of these crashes that _does_ happen on RELEASE builds that I haven’t yet been able to reduce.
>>> 
>>> 
>>> On Wed, Nov 29, 2017 at 4:43 PM Tony Parker <anthony.parker at apple.com <mailto:anthony.parker at apple.com>> wrote:
>>> Hi Brandon,
>>> 
>>> This is probably a bug in the CoreFoundation C sources part of swift-corelibs-foundation. Unlike Darwin platforms, we can’t make the CFSTR(“”) macro produce a CFStringRef that cannot be overreleased. Probably there is a constant string returned from CF function, then the Swift runtime assumes it can release it, and bam we wind up with an overrelease.
>>> 
>>> We’ll have to track down which function is getting called, which probably just requires stepping through that test case with a debugger…
>>> 
>>> - Tony
>>>> On Nov 29, 2017, at 1:34 PM, Brandon Williams via swift-corelibs-dev <swift-corelibs-dev at swift.org <mailto:swift-corelibs-dev at swift.org>> wrote:
>>>> 
>>> 
>>>> Hello all!
>>>> 
>>>> We’ve been encountering this runtime error quite a bit recently, and we have no idea why. We’ve filed a bug and there’s one other on JIRA related to this, but both without any comments:
>>>> 
>>>> https://bugs.swift.org/browse/SR-6422 <https://bugs.swift.org/browse/SR-6422>
>>>> https://bugs.swift.org/browse/SR-6398 <https://bugs.swift.org/browse/SR-6398>
>>>> 
>>>> We’re curious if others are aware of this and or has more info? Is it a red herring for some other problem?
>>>> 
>>>> Any info would be helpful!
>>> 
>>>> _______________________________________________
>>>> swift-corelibs-dev mailing list
>>>> swift-corelibs-dev at swift.org <mailto:swift-corelibs-dev at swift.org>
>>>> https://lists.swift.org/mailman/listinfo/swift-corelibs-dev <https://lists.swift.org/mailman/listinfo/swift-corelibs-dev>
>> 
>> _______________________________________________
>> swift-corelibs-dev mailing list
>> swift-corelibs-dev at swift.org <mailto:swift-corelibs-dev at swift.org>
>> https://lists.swift.org/mailman/listinfo/swift-corelibs-dev <https://lists.swift.org/mailman/listinfo/swift-corelibs-dev>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-corelibs-dev/attachments/20171201/f80c6ef7/attachment.html>