Gentoo Archives: gentoo-alt

From: Fabian Groffen <grobian@g.o>
To: gentoo-alt@l.g.o
Subject: [gentoo-alt] [PREFIX] the road ahead for Darwin/macOS
Date: Fri, 27 Dec 2019 10:45:58
1 To all interested in Gentoo Prefix on recent macOS.
3 In the past few releases of macOS, /usr/include has disappeared. While
4 this previously was remedied by performing some commands, Apple has made
5 this more strict, and it appears the way forwards, is by no longer
6 relying on /usr/include.
8 To deal with this, the packages sys-kernel/xnu-headers and
9 sys-libs/darwin-libc-headers were added to @system for newer macOS
10 profiles. While you may have seen these packages coming in, getting
11 some updates here and there, they may still not be perfect, yet I think
12 we're getting somewhere. The purpose of these packages obviously is to
13 provide system headers and frameworks without relying on Xcode.
15 Next I've modified the bootstrap script to unpack a Prefix-built clang
16 compiler, and use it to bootstrap. This, in addition to the headers,
17 allowed me to progress until stage2 where a compiler is built. This
18 failed, for a number of reasons. 1) requirement of cmake, which is
19 horrible. It requires way too much in terms of dependencies, so I
20 resorted to an unpacked Prefix-built version to provide it. Can't use
21 upstream's binaries for cmake, because they insist on using Xcode SDKs.
22 Next, 2) clang fails to build halfway because it throws away CXXFLAGS
23 pointing to the headers provided. I seem to remember that this is what
24 GCC build does as well, so not that surprising, but it basically renders
25 the approach useless.
27 This lead me to investigating how to tell the bootstrap compiler to keep
28 looking for the headers we provided. Turns out the compiler is
29 hard-wired to add c++ headers (stdinc) to its search-path, and this is
30 necessary (at least on Darwin) because the math.h header appears twice,
31 and only one of them is compatible with c++ code. Anyway. Apple seems
32 to use -isysroot to point to an SDK that's selected/targetted. It seems
33 to me, at this point we should follow that lead, and simply turn the
34 Prefix into such sysroot. Experimenting with this option on our
35 Prefix-build clang, results in not exactly desirable behaviour. Because
36 the offset prefix is added to the compiler's search paths, nothing ends
37 up right.
38 So I downloaded clang binary from, and tried the same. That
39 made more sense, and it seems the search path is correct there.
41 What I want to try now, is if I can set CC/CXX to "clang -isysroot
42 /path/to/prefix", and if that will get me through compiler building of
43 stage2 during bootstrap.
45 If that works, it seems the first step towards Xcode free bootstrapping
46 on macOS. There will be some questions towards how we build our clang,
47 if we should step away from patching it and using isysroot instead.
48 Finally, how we're going to provide the binaries that we want to use
49 during bootstraps. Ideally we can provide stage1/stage2 by simply
50 installing form binpkgs, for instance using q/portage-utils.
52 End of update, hopefully bootstrapping can be working again soon.
54 Thanks,
55 Fabian
57 --
58 Fabian Groffen
59 Gentoo on a different level


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Subject Author
Re: [gentoo-alt] [PREFIX] the road ahead for Darwin/macOS Fabian Groffen <grobian@g.o>