lldb fails to run properly on macOS

[tromey]

I installed the rust-enabled lldb from rustup and tried to run it. It crashes with the mysterious:

(lldb) command script import "/Users/ttromey/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/etc/lldb_rust_formatters.py"
: CommandLine Error: Option 'limited-coverage-experimental' registered more than once!
LLVM ERROR: inconsistency in registered CommandLine options
Assertion failed: (e == 0), function ~recursive_mutex, file /BuildRoot/Library/Caches/com.apple.xbs/Sources/libcxx/libcxx-400.9/src/mutex.cpp, line 64.
libc++abi.dylib: Pure virtual function called!

This seems to be a known LLVM bug: https://bugs.llvm.org/show_bug.cgi?id=22952. See also https://bugs.llvm.org/show_bug.cgi?id=30587. This is fallout from the switch to a dynamic LLVM, #53245.

I can't reproduce in my Linux build; not sure what is different there.

I'm looking into workarounds. One option might be to hack our clang and lldb builds so that all libraries are marked DISABLE_LLVM_LINK_LLVM_DYLIB.

[tromey]

Can't reproduce with a local macOS build either. I'm still investigating.

I wonder if it's possible to build clang and lldb out-of-tree as is done for lld.

[tromey]

If I run the rustup-installed lldb without going through rust-lldb, it works.

[tromey]

Aha, invoking the command script import ... command that rust-lldb provides is what causes the crash. Which I guess could be apparent from the original failure.

[tromey]

Just a simple Python file with import lldb makes it crash, so my theory is that something is wrong with our lldb build, causing this to try to load some other liblldb.dylib.

[tromey]

The bug is that rustup does not preserve symlinks when installing lldb.

[tromey]

This is strange, though, because rustup and tar seem to have symlink logic.

[tromey]

The package manifest contains file:.../_lldb.so, so maybe this needs to be extended to allow a symlink somehow.

[tromey]

I think the answer ends up being that rustup-utils/src/utils.rs should understand how to copy a symlink.

[tromey]

I have a rustup patch I will test out tomorrow.

[tromey]

rust-lang/rustup.rs#1504

[michaelwoerister]

Do you think this can be solved without going back to linking to LLVM statically?

[tromey]

Yes, see the PR -- once rustup can handle symlinks it should work.

I'm waiting for a new rustup release; then I'll test it again; and then if there aren't any more failures I'll write an announcement.

[michaelwoerister]

OK, great! So we don't need to revert that.

[vadimcn]

I wonder if this would fix it.

[tromey]

Thanks, that does seem promising. I've been waiting for a new rustup release, though, since I was able to fix it locally using rust-lang/rustup.rs#1504. But maybe landing that lldb patch would be faster.

[tromey]

This is fixed by rustup 1.14.0, which shipped yesterday.