Consider using different Docker tags for ARM and x86_64 platforms

[frol]

I have just noticed that the Dockerfile pulls Rust and GCC toolchains for ARM platform along with x86_64. There are a few points why I find it cumbersome:

• The image size is noticeably affected.
• The popular libraries are only built for x86_64, thus the ARM target is not on par with x86_64.

[emk]

Yeah, this is a bit of an open question still. The ARM code was submitted by a very kind user, and I have an actual use case for it myself. But we don't yet have a generalized mechanism to support all C libraries on both platforms yet—possibly because there's much less demand for most of those C libraries on ARM.

This will probably get redesigned at some point to be cleaner. But it's not at the top of my priority list.

[KEINOS]

I understand the priority and would like to respect that. Thanks for the effort of maintening it. On the other hand, I would like to +1 for this consideration.

On Mac:

$ docker pull ekidd/rust-musl-builder:stable
$ docker run --rm -it ekidd/rust-musl-builder:stable /bin/bash
rust@526deb2c064b:~/src$ 

The container boots straight with no problem. Then I was able to multi-stage-build the RipGrep to make it work on Alipine. And it worked like a charm.

Thanks for rust-musl-builder and the documentation. With this container, even for the rust begginer like I, it was amazingly easy to build the rust env and it's bin.

standard_init_linux.go:190: exec user process caused "exec format error" on RPi

Though on RPi3 Jessie:

$ docker pull ekidd/rust-musl-builder:stable
$ docker run --rm -it ekidd/rust-musl-builder:stable /bin/bash
standard_init_linux.go:190: exec user process caused "exec format error"

😭 I got the above error and drifted to this issue. I think this error comes from the same reason with this isse.

Env info

```shellsession $ cat /etc/os-release PRETTY_NAME="Raspbian GNU/Linux 8 (jessie)" NAME="Raspbian GNU/Linux" VERSION_ID="8" VERSION="8 (jessie)" ID=raspbian ID_LIKE=debian HOME_URL="http://www.raspbian.org/" SUPPORT_URL="http://www.raspbian.org/RaspbianForums" BUG_REPORT_URL="http://www.raspbian.org/RaspbianBugs" $ uname -a Linux RaspberryPi 4.14.41-v7+ #1113 SMP Thu May 17 16:29:48 BST 2018 armv7l GNU/Linux ```

[humb1t]

standard_init_linux.go:211: exec user process caused "exec format error"

The same thing with nightly on RPI4

[emk]

Ouch. I'm really sorry to hear about this, and I'd be happy to review a PR improving the ARM situation. ARM is a great architecture with lots of uses, and I'd love to have support for it. And I really appreciate the effort that everybody has put into bug reports.

But I don't see much chance of me getting to this in a reasonable amount of time. :-( My apologies.

[emk]

Due to a number of problems with the ARM support, including the fact that it provided very few libraries compared to the Intel toolchain—and the fact that I have neither the time nor an ARM system to maintain it properly—I've gone ahead and dropped ARM support.

I would consider adding it back if someone has a plan for (1) release it under a different tag, (2) supporting the same C libraries as the Intel version (more or less), and (3) automatically testing it for each release.