Segfault of __thread varaible in Linux/ARM due to bug of LLVM ARM code generation

[Geunsik Lim]

There are four thread local storage (TLS) models in Clang/LLVM as following:
1) global-dynamic TLS model
2) local-dynamic TLS model
3) local-exec TLS model
4) initial-exec TLS model
and emulated-TLS (for Android S/W platform)??

Even though, We can build run normally with the static relocation method by selecting the initial-exec TLS model instead of global-dynamic TLS model (by default) , We need to run the clang application code with global-dynamic (or local-dynamic) TLS model in order that we support some applications is working with dlopen(3) library call.

We have found the appropriate solution for some clang/LLVM applications including 1) __thread variables and 2) -O2/-O3 of the clang language. Could you apply this patch to Ubuntu 14.04 LTS and Ubuntu 16.04 LTS repository?

* LLVM: Revision 268662 (ARM: don't attempt to merge litpools referencing different PC-anchors.)
http://llvm.org/viewvc/llvm-project?view=revision&revision=268662
https://llvm.org/bugs/show_bug.cgi?id=27836
https://llvm.org/bugs/show_bug.cgi?id=28035

Below is the mailing list discussed to fix this issue.
http://lists.llvm.org/pipermail/llvm-dev/2016-May/098974.html
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20160502/353476.html
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20160509/355091.html
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20160516/356679.html

* Before r268662:
  ubuntu@raspberrypi2#> ./corerun ./hello.exe (with -O2/-O3)
  Segmentation Fault

* After r268662:
  ubuntu@raspberrypi2#> ./corerun ./hello.exe (with -O2/-O3)
  Hello!!! Welcome to .NET Core (CoreCLR) world.!!!

[Geunsik Lim (leemgs)]

Here is additional information.

Runtime (CoreCLR) of .NET Core is available at https://github.com/dotnet/coreclr.

Clang/LLVM3.6.2 (for Ubuntu 14.04 X64) binary that I re-compiled the existing Clang/LLVM is available at https://onedrive.live.com/redir?resid=C93799B86B006829!191&authkey=!AKb-qFmpFRUGDtM&ithint=file%2cbz

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "[LLVM] Linux/ARM: don't attempt to merge litpools referencing different PC-anchors." seems to be a patch. If it isn't, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are a member of the ~ubuntu-reviewers, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issues please contact him.]

[Geunsik Lim (leemgs)]

This patch is to fix the incorrect __thread variable operation of Clang/LLVM for Linux/ARM.

[Geunsik Lim (leemgs)]

Created attachment 16399
ARM: don't attempt to merge litpools referencing different PC-anchors.

There are four thread local storage (TLS) models in Clang/LLVM as following:
1) global-dynamic TLS model
2) local-dynamic TLS model
3) local-exec TLS model
4) initial-exec TLS model
and emulated-TLS (for Android S/W platform)??

Even though, We can build run normally with the static relocation method by selecting the initial-exec TLS model instead of global-dynamic TLS model (by default) , We need to run the clang application code with global-dynamic (or local-dynamic) TLS model in order that we support some applications is working with dlopen(3) library call.

We have found the appropriate solution for some clang/LLVM applications including 1) __thread variables and 2) -O2/-O3 of the clang language. Could you apply this patch to Ubuntu 14.04 LTS and Ubuntu 16.04 LTS repository?

* LLVM: Revision 268662 (ARM: don't attempt to merge litpools referencing different PC-anchors.)
http://llvm.org/viewvc/llvm-project?view=revision&revision=268662

Below is the mailing list discussed to fix this issue.
http://lists.llvm.org/pipermail/llvm-dev/2016-May/098974.html
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20160502/353476.html
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20160509/355091.html
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20160516/356679.html

* Before r268662:
  ubuntu@raspberrypi2#> ./corerun ./hello.exe (with -O2/-O3)
  Segmentation Fault

* After r268662:
  ubuntu@raspberrypi2#> ./corerun ./hello.exe (with -O2/-O3)
  Hello!!! Welcome to .NET Core (CoreCLR) world.!!!

[Geunsik Lim (leemgs)]

We have posted this issue and patch to Ubuntu's launchpad bug system (e.g. llvm-defaults package) as following:
* https://bugs.launchpad.net/ubuntu/+source/llvm-defaults/+bug/1584089

[Geunsik Lim (leemgs)]

https://llvm.org/bugs/show_bug.cgi?id=27836

[Geunsik Lim (leemgs)]

Adding: Tim Northover <email address hidden>

[Tim Northover (t-p-northover)]

As noted, this was fixed by r268662.

[Geunsik Lim (leemgs)]

I have added "Ubuntu Toolchain Hackers".

[Geunsik Lim (leemgs)]

I have evaluated the effect the patch after uploading the updated packages to my PPA.
The evauation result was Okay.
* https://launchpad.net/~leemgs/+archive/ubuntu/dotnet/+packages