Add linux-musl build leg

[weshaggard]

cc @eerhardt @janvorli

fyi @RussKeldorph

[sdmaclea]

Any comment on this ? Is this intended to be experimental ? New direction ?

[ghost]

@sdmaclea, trivia: it started at dotnet/core#1331, moved to https://github.com/dotnet/core-setup/issues/3817, assembly names discussion https://github.com/dotnet/corefx/issues/28554, RIDs updated with linux-musl PR dotnet/corefx#28560 and corresponding corefx PR to this change: dotnet/corefx#29168.

In short:

• linux-x64 continues to mean "linux x64 with glibc-ism", no change there
• linux-musl-x64 triplet, which does not inherit from linux-x64 but instead is its sibling, means "linux x64 with muscle libc"

In future, we can add dietlibc, uclibc, bionic-libc etc. to give some room for non-gnu-ism, other POSIX candidates: busybox, toybox etc.

[eerhardt]

@kasper3 - that is a pretty good summary of the activity. However, one piece was incorrect:

linux-musl-x64 triplet, which does not inherit from linux-x64 but instead is its sibling,

Actually, linux-musl-x64 does inherit from linux-x64. See the RID hierarchy here and the reasoning/justification in the discussion starting here.

[eerhardt]

Note - the over-arching idea here is to not produce "alpine" branded packages/tarballs. Instead these binaries and packages are intended to work across any musl based Linux. So we are in the process of renaming "alpine" in the packages to "linux-musl". The steps are:

1. Add the new linux-musl packages.
2. Do this throughout the stack to keep it building. (coreclr -> corefx -> core-setup -> CLI)
3. Remove the "alpine" packages in the reverse order. (CLI -> core-setup -> corefx -> coreclr)

This way nothing breaks during the rename process.

[ghost]

While building CoreCLR, should we expect output directory to be bin/Product/Linux.musl.arm.Debug/ or bin/Product/Linux.arm.Debug/? If former is expected than I am getting latter with current master.

[weshaggard]

@kasper3 what command are you building with? Also it looks like you are trying to build linux-musl for arm which currently we are only building it for x64.

[ghost]

@weshaggard, I noticed when working on #17730. Using build steps from https://github.com/dotnet/coreclr/issues/17468#issuecomment-382831060 on troyfontaine/armhf-alpinelinux docker (it's pure alpine 3.7 arm32 with additional qemu layer for x64), and changes from my branch; coreclr built successfully.
Was just wondering if OutputDir should also have a different name on alpine (as in on x64; Linux.musl.x64.Debug)?

[weshaggard]

I'd expect it to be Linux.arm.Debug as we only take into account the general OS name in the output directory not the full RID so it would just be "Linux"

[AddRemover]

I am looking for a dotnet runtime compliled to run on arm32 bin with musl.
The target is to run one .net app on my OpenWRT router Linksys WRT3200ACM which is arm32.
So, I can't use musl-arm64, I need musl-arm32.