s390x toolchain generates binaries for GLIBC 2.18 which is incompatible with RHEL 7

[ancwrd1]

In the zLinux world the Red Hat Interprise Linux 7 is a very common distro. Unfortunately it comes with GLIBC 2.17 so the binaries created with the cross tool cannot be run due to some missing symbols.

[Hoverbear]

Seems similar to #455

[Alexhuszagh]

This might be an issue for a few reasons:

1. Need to change package management for s390x-unknown-linux-gnu to CentOS 7.
2. There are no provided packages for glibc-s390x-linux-gnu in any official repository, and gcc-c++-s390x-linux-gnu only exists (without the shared libraries) in EPEL.

This means compiling glibc from source, which means we'd probably be better off using crosstool-ng entirely, which is quite a lot of work. It's definitely not impossible, and I'll add a section to the wiki about how to use older toolchain versions, but I don't think we can support this out-of-the-box: it's too much new code, a new dependency, and too much maintenance long term.

[Alexhuszagh]

This is relatively more complex than desired, because there's a lot of bugs in crosstool-ng due to a lack of maintenance (such as old isl and expat versions), and would require essentially all the patches I've made for my C++ analog of cross (which patch numerous version dependencies and other bugs) Simply put, unless there's a lot of demand, it's probably not worth documenting since it requires a lot of effort, manual fixes to upstream tools, and debugging.

[Alexhuszagh]

Update: we're going to be using crosstool-ng anyway to fix other issues (see #426), so although we won't support it, I can get some sample files showing how to build this with ct-ng 1.24.0. This will allow you to create a custom docker image with minimal work for this purpose, which will be documented on the wiki.

[ancwrd1]

Thanks for the feedback. With docker and cargo cross it's certainly easier; we are currently using a custom crosstool-ng toolchain for s390x which implies some additional setup with cargo config, environment variables, etc.

[Alexhuszagh]

Sounds perfect, I'll document it in the wiki and create my own repository with config and Dockerfiles for these, so others can plug-and-play to use them. It'd slow down our CI by a lot, and also it's a lot of maintenance for so many builds long term, but I think it's a good idea since most of our infra is already done here.

EDIT: I've gotten approval to make it on cross-rs proper in a separate repo, so this should be a little more official.

[Alexhuszagh]

Sorry for the large number of notifications.

I've tried this build and there's issues compiling for glibc versions <= 2.19, due to missing definitions for dtv_t and others, presumably because __ASSEMBLER__ is erroneously defined, in nptl/sysdeps/s390/tls.h. This file was removed in glibc 2.20, and the builds work starting there.

I really don't have time to patch glibc to do this, or find a way to fix this preprocessor definition, so if you have a working config file or patch, I'd be happy to use it. In the meantime, we'll show how to support newer glibc versions, but older ones like 2.17 can't be easily supported right now.

[ancwrd1]

No problem, thanks for your efforts and help.