[gentoo-musl] [GSoC] native-clang: daily report 07/18

[Lei Zhang]

Plan for today:
- build a stage4

Progress:
- (thanks to jmbsvicetto's advice on #gentoo-releng) install clang and
related libs in a vanilla musl stage3, make clang the default
compiler, try to rebuild @world, fix packages that fail, and build a
stage4 based on that customized stage3

Surprisingly, when rebuilding @world with the native clang, only two
packages failed: iproute2 and llvm itself, which are not hard to fix
:)

iproute2 depends on libmnl, which is mis-compiled by clang. This is a
known issue, and easy to fix: just compile libmnl with gcc. Or
alternatively, apply USE=minimal on iproute2 so it doesn't depend on
libmnl. For more info:
https://bugs.chromium.org/p/chromium/issues/detail?id=548786

As for llvm, certain components of it depend some symbols provided by
libgcc_s, but unavailable in libunwind, including __regsiter_frame and
__deregister_frame. Interestingly, these symbols are provided by
llvm's version of libunwind. Anyway, I'm using the non-llvm libunwind
now just for convenience, and this problem is easy to fix: build all
llvm libs as static libs, and disable the llvm bitcode interpreter
(lli). This fix doesn't affect the functionality of clang. I may
revisit this issue later and see how llvm's libunwind work.

The building of stage4 went quite smoothly as well. It seems stage4
doesn't require rebuilding of the kernel, so using clang as the
default compiler causes no problem so far.

Plan for tomorrow:
- test the stage4
- submit my ebuilds to the GitHub repo


Lei