Swift 5.5 has serious stack corruption bugs!

Panajev · 2021-10-02T06:30:00.489Z

Hello Doug, one quick followup to your welcomed and very detailed explanation. Will this require iOS 15.1 as minimum SDK target or is it something that can be fixed in a compiler / Xcode update only?

taylorswift · 2021-10-02T21:45:12.037Z

Douglas_Gregor:

We greatly appreciate the bug reports provided here by @taylorswift, which have helped us track down a previously-unknown miscompile with asynchronous calls. We have a fix that addresses all of the bugs reported at the beginning of this thread, and we'll look to roll it out as soon as it is feasible.

this is incredible news! kudos to the compiler team for the fast turnaround once these issues were brought to light.

Douglas_Gregor:

There is a lot of unhelpful hyperbole here in this thread. Bugs happen, even in compilers, and regardless of how long a feature has been in production you will still eventually be shocked to find that there's a carefully-crafted 5-line program that triggers a problem.

i apologize for my part in contributing to the excessively heated rhetoric in this thread. and having been told of the spillover on twitter from thursday, i completely agree that the discourse there devolved into a lot of unhelpful dunking. at the same time, i don’t really think it’s necessary to go back and downplay or minimize the issues people faced in the beginning, especially now that we have a fix on hand.

vine:

If it is fixed in version 5.5.1, will it affect performance?

i for one, would rather have slow, but correct code, than fast but buggy code.

johnburkey · 2021-10-06T17:26:00.771Z

Let's be careful here- we know this particular bug escaped into the wilds - and we know that async await is new, and that means there aren't alot of codebases available to test it. Lets get these fixes into Xcode betas and iterate. Given the scope of this work, and the speed with which it caused problems in the wild, there are probably more bugs hiding behind this one.

And all of us who can in the community, try it out and test.

Douglas_Gregor · 2021-10-06T20:01:53.259Z

Panajev:

Hello Doug, one quick followup to your welcomed and very detailed explanation. Will this require iOS 15.1 as minimum SDK target or is it something that can be fixed in a compiler / Xcode update only?

It's a compiler-only change with no impact on any OS.

Doug

taylorswift · 2021-10-06T20:26:46.423Z

Douglas_Gregor:

We have a fix that addresses all of the bugs reported at the beginning of this thread, and we'll look to roll it out as soon as it is feasible.

hi, i just tested with the Oct 5 nightly snapshot, which is the first since that PR was merged, and the issues are still present. the commit hashes are

$ swiftc --version
Swift version 5.6-dev (LLVM 7aef0efea99e2c6, Swift e4f71c8e118fc09)
Target: x86_64-unknown-linux-gnu

i’m not sure if the LLVM hash 7aef0efea99e2c6 is before or after the fix was merged

Douglas_Gregor · 2021-10-06T20:29:02.604Z

taylorswift:

$ swiftc --version
Swift version 5.6-dev (LLVM 7aef0efea99e2c6, Swift e4f71c8e118fc09)
Target: x86_64-unknown-linux-gnu
i’m not sure if the LLVM hash 7aef0efea99e2c6 is before or after the fix was merged

This snapshot did not have the fix.

Doug

taylorswift · 2021-10-06T20:31:13.758Z

okay! thanks for clarifying!

bowman_on_jupiter · 2021-10-10T09:57:21.771Z

Tested on M1 with Xcode 13/ iOS 15 with below Swift 5.5 version seems doesn't hit the 1st issue
swift-driver version: 1.26.9 Apple Swift version 5.5 (swiftlang-1300.0.31.1 clang-1300.0.29.1)
Target: arm64-apple-macosx11.0

taylorswift · 2021-10-14T19:38:23.554Z

hi, i’ve successfully built an updated toolchain against llvm stable/20210726, and i can confirm that 3 out of 4 of the bugs listed in the beginning of this thread are no longer present.

~~SR-15225~~
~~SR-15241~~
~~SR-15240~~

i’ve gone ahead and closed those three issues on the bug tracker.

it appears that SR-15266, the SIMD segfault, is still present, even with the LLVM fix. (@timdecode)

i do not know if the bugs discovered by @mickeyl are still present.

mickeyl · 2021-10-15T10:23:47.662Z

Good news! Do you perhaps have webspace to upload the toolchain somewhere? I'd like to verify my issues.

taylorswift · 2021-10-15T16:49:44.037Z

mickeyl:

Good news! Do you perhaps have webspace to upload the toolchain somewhere? I'd like to verify my issues.

what platform are you on? i only have binaries for Ubuntu 20.04

George · 2021-10-15T17:11:23.197Z

I'd appreciate Ubuntu 20.04 binaries... any chance you can push a docker image to docker hub? (May not be a huge deal... I assume swiftlang/swift:nightly-focal-main won't be stuck at 10-5 forever...)

taylorswift · 2021-10-16T22:39:21.077Z

i don’t know how to create a docker image, but here is zip file with the 20.04 toolchain i am using:

drive.google.com

swift-LOCAL-2021-10-14-a-linux.tar.gz

Google Drive file.

johnburkey · 2021-10-18T23:52:51.730Z

Xcode 13.1 RC have the fixes you mentioned above?

Douglas_Gregor · 2021-10-19T00:10:53.952Z

johnburkey:

Xcode 13.1 RC have the fixes you mentioned above?

Yes.

Doug

johnburkey · 2021-10-19T00:12:29.920Z

cool, will test.

johnburkey · 2021-10-19T00:14:21.220Z

Any idea which linux build we can test with as well?

timdecode · 2021-10-19T01:12:27.876Z

I can confirm the SIMD bug is still there (expectedly) in Xcode 13.1 RC. Thanks for checking it out on llvm stable.

Finagolfin · 2021-10-19T09:02:05.621Z

I assume Xcode 13.1 has a recent snapshot from the 5.5 branch: there have been regular 5.5 snapshot builds available for linux, most recently a couple days ago.

timdecode · 2021-10-26T18:33:46.419Z

I just checked the new release version of Xcode 13.1 (13A1030d) and it still has the SIMD bug.