[gentoo-musl] Proposal for official "native clang" support

[Bjorn Pagen]

Dear everyone,

A few months ago, I had embarked on a quest to find (or create!) a
reasonable linux distribution that was completely based on clang, with no
dependence on gcc whatsoever. My search turned up empty, but there were the
seeds of hope in Gentoo. Previous developers had brought native clang
support to gentoo, and there were ways to make clang the native toolchain,
thanks to the clang native GSoC.

The problem is that despite all this, gentoo's support for a clang-native
toolchain in currently distributed stages is still very bad. It is
impossible to change the toolchain to a clang based one without some major
hacking and bootstrapping, which is something that I'm sure no one wants to
do. This is because is not possible to compile a self-hosting clang
toolchain with gcc, which means that an average gentoo user could never use
clang as system default without still depending on gcc.

As a consequence, if a gentoo user wanted to use clang native, they would
have to stumble across a reddit post, made either by me or stalmannen,
distributing experimental stages.

Over these past few months, I have spent much time troubleshooting and
bug-fixing to create a fully clang-native gentoo stageball, based on a
clang/LLVM/musl/lld toolchain. I have gotten it to the point where I
believe it can now be officially supported by gentoo, at least as an
"experimental stage".

   - It is self hosting, via a bootstrap.sh script I have made. I am hoping
   to eventually change this into a GRS script, but I am still working on it.
   - I use my own profiles, which are located in /usr/portage/profiles, and
   inherit from amd64/default/musl. They remove gcc, binutils, and others from
   the system set, and replace them with llvm/clang/lld, etc. I'm hoping they
   can be moved into the main portage tree eventually.
   - There is really no "hacking" neccessary to make the stage work. Out of
   the box, it can compile stuff, and otherwise behave exactly like a regular
   musl stage.
   - The whole system set compiles except for 2 packages: sandbox and
   pambase. The sandbox bug is trivial (#643740), and is just a problem in a
   configure script detecting libc path. The pambase bug is less trivial (no
   open bug), and I have no idea how to fix it.
   - There are some "hacks" in /etc/portage, such PIE/SSP patches for
   clang, and symlinks from nm -> llvm-nm, ar -> llvm-ar,
   /usr/lib/clang/libclang_rt.a -> /usr/lib/libcompiler_rt.a, but all of these
   hacks will go away with some more bug fixing and upstream changes.

The biggest reason I propose native clang stages to be hosted by gentoo is
so it can gain more publicity, and attract the attension of more
developers. I really want clang linux to become a reality, but I am only
one guy, and can torture myself over so many bugs.

Link to my reddit post for details:
https://www.reddit.com/r/Gentoo/comments/7qdrun/update_to_clangmusl_experimental_stage4/

Link to GSoC by zlei:
https://blogs.gentoo.org/gsoc2016-native-clang/

Here's a link to a google drive folder containing a few stages and the
bootstrap script.
https://drive.google.com/drive/folders/1Hv8obFaiKf9iNOFqLhOcFh69nEWRFMWJ?usp=sharing

Here's a link to the bootstrap script.
https://drive.google.com/file/d/1jV0D4W-pB7cV2Q1yztL5ysRt8rzqzaxe/view?usp=sharing

Here's a link to my latest build (Jan 28):
https://drive.google.com/file/d/1RyB1sLgeBsfc8_RwsJJ0V29bAq34frbJ/view?usp=sharing

SHA512 for latest build (Jan 28):
51a3ca5547f221b7ceea7691d4f4a3d20ba6aa50fac3c95bb67fd2e5aeb331d2d50fce173e579b5e
cfa05aa4b410f22e9b6fa4cd7edeefefb0c697f5128d61e1

-- 
Thanks a ton,
Bjorn Pagen