Test statically linked clang outside of Alpine Linux

[nathanchance]

We should verify that we can use the toolchain produced in Alpine Linux
on other distributions as part of the continuous integration pipeline.

We download the toolchain out of the container, mount it into the
containers that we want to test it in, and test dynamically and
statically linking hello.{c,cpp} with musl. Eventually, glibc should be
tested but there are issues during the link phase.

Initially, the only container that is being tested is Fedora. However, I
intentionally wrote this in such a way that we should be able to use
this across multiple distributions and test more than just
hello.{c,cpp}.

This was tested on a self-hosted GitHub Actions runner:

https://github.com/nathanchance/containers/actions/runs/2387476728

[nickdesaulniers]

wow thanks! Looks good. doesn't matter to me if my feedback is handled in this PR or follow ups.

Feel free to re-kick the build once this is merged, too!

[nathanchance]

Alright, I should have addressed all outstanding comments. Please take a look.

[nathanchance]

a6a0b02 addresses an issue I noticed while bringing up arm64 support on a self-hosted runner. It looks like it is not possible to use the Docker action just to push and they appear to have no intention of supporting that but this is an easy enough workaround.

[nickdesaulniers]

What about --sysroot? Can --sysroot=/usr/lib/musl subsume all of -B, -I, -L?

[nathanchance]

I'll test.

[nathanchance]

--sysroot works for Arch Linux:

https://github.com/nathanchance/containers/runs/6630314825?check_suite_focus=true

But not Fedora, likely due to lib64 instead of lib?

https://github.com/nathanchance/containers/runs/6630479212?check_suite_focus=true

[nickdesaulniers]

I'll file a todo to see what we can do to simplify this. Basically, if we want to support kernel builds for make LLVM=1 and not just make CC=clang with this (i.e. HOSTCC=clang) we might have to add these somehow.

Though perhaps I'm getting ahead of myself, and they can simply just use --target=x86_64-linux-gnu and it will work just fine.

Perhaps we need to find the most portable way of finding the expected target triple for a given system. Is it glibc based or musl based? Is $(CC) -print-target-triple the most portable way to find out? Is there a way to find out without a compiler installed? IDK

example
$ clang --target=$($(CC) -print-target-triple

so that our default implicit target doesn't matter.

[nathanchance]

Perhaps we need to find the most portable way of finding the expected target triple for a given system.

Right, I think this is the root of the problem: for HOSTCC=clang, we don't set a triple, we rely on the implicit default, which is not going to work if we want to support both glibc and musl with this toolchain.

Is it glibc based or musl based?

I suppose one option would be trying to look at a binary for GLIBC symbols but that feels like a massive hack...

We could potentially make this work with a wrapper like musl ships? On my host:

$ cat $(which musl-clang)
#!/bin/sh
cc="clang"
libc="/usr/lib/musl"
libc_inc="/usr/lib/musl/include"
libc_lib="/usr/lib/musl/lib"
thisdir="`cd "$(dirname "$0")"; pwd`"

# prevent clang from running the linker (and erroring) on no input.
sflags=
eflags=
for x ; do
    case "$x" in
        -l*) input=1 ;;
        *) input= ;;
    esac
    if test "$input" ; then
        sflags="-l-user-start"
        eflags="-l-user-end"
        break
    fi
done

exec $cc \
    -B"$thisdir" \
    -fuse-ld=musl-clang \
    -static-libgcc \
    -nostdinc \
    --sysroot "$libc" \
    -isystem "$libc_inc" \
    -L-user-start \
    $sflags \
    "$@" \
    $eflags \
    -L"$libc_lib" \
    -L-user-end

I suspect that might make the regular kernel build unhappy but maybe not?

[nickdesaulniers]

LGTM 🌳 🌲

[nickdesaulniers]

@nathanchance do you want to manually kick the workflow to trigger a run of this?

[nickdesaulniers]

ah, I see you did!
https://github.com/ClangBuiltLinux/containers/actions/runs/2398394189
👍

[nathanchance]

I'll keep an eye on it to make sure everything works!