Fix configure --llvm-root

[pnkfelix]

Rust currently uses a patched version of llvm. Some time ago, we added a --llvm-root option to configure (#1123), to allow the user to point the build at an LLVM outside the build tree.

Some recent discussion on #4259 and on wiki packaging leads me to conclude that the llvm-root switch is broken.

We may want to fix it, e.g. to test, once our patches have landed upstream, whether a new version of LLVM works.

(Also, I would be curious if there is a way to build the LLVM source once and share it amongst multiple clones of the Rust git repository. Doing that was the impetus for my interest in this matter, though in hindsight it is possible that --llvm-root never actually supported that use-case.)

[fabiand]

I'll be happy to test anything related to unbundling llvm.

[bblum]

nominating feature-complete milestone

[catamorphism]

Just a bug -- internal implementation issue.

[fabiand]

Fixing this would really help us to get rust into fedora. A bundled llvm is a major blocker.

Tim Chevalier notifications@github.com schrieb:

Just a bug -- internal implementation issue.

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[alexcrichton]

Sadly, until we get our patches into LLVM upstream we won't be able to do this.

[pnkfelix]

Well, I would think we could fix the --llvm-root switch, regardless of whether the patches are upstream. I.e. being able to make one checkout of our fork and share it among multiple clones of rust. (I'm just pointing out that #4259 does not actually block this.)

[fabiand]

Will the --llvm-root actually require all llvm source, or just the headers+libs?

[alexcrichton]

In theory all we need are the headers and libraries, the source shouldn't be necessary at all.

[dmski]

--llvm-root is actually working fine for me on macos and linux (though i last checked it on linux about 2 months ago).

I have llvm built with ./configure --enable-targets=x86,x86_64,arm,mips --enable-optimized --enable-assertions --disable-docs --enable-bindings=none --disable-terminfo --disable-zlib --disable-libffi --with-python=/usr/bin/python2.7 --prefix=/path/to/installed/llvm and installed to a separate directory.

Building rustc with configure --llvm-root=/path/to/installed/llvm then skips building and configuring llvm (though still retrieves its sources from git) and resultant rust binaries successfully pass make check.

[alexcrichton]

Indeed, we're using --llvm-root on travis today, and we're doing just fine.