using rustbuild breaks compiling against system llvm when linked against libffi

[hussamT]

I get the following error:
rust undefined reference to `ffi_type_double'

There was a workaround that helped in the past but it doesn't anymore.

[nagisa]

That’s most likely because your system llvm-config does not print -lffi in

$ llvm-config --system-libs
-lrt -ldl -lcurses -lpthread -lz -lm -lffi

That’s a bug in your system LLVM. Workaround is to put something like

#!/usr/bin/bash
/usr/bin/llvm-config "$@" | sed 's/-lm/-lm -lffi/'

in your path (so the script would execute instead of the actual llvm-config, when llvm-config is invoked)

[hussamT]

I will try that now. Than you.
Edit: It didn't help. Maybe I need to patch llvm instead?

[kyrias]

Yeah, I'm currently trying to build rust 1.15.1 for Arch, and I've tried both the old setting RUSTFLAGS to -C link-args=-lffi approach, and making llvm-config a wrapper script that adds it, but neither works anymore. Not sure how it decides the CFLAGS it uses now.

[hussamT]

I noticed Fedora is using --disable-rustbuild http://pkgs.fedoraproject.org/cgit/rpms/rust.git/tree/rust.spec#n260 which retains the old behavior.

[kyrias]

Just discovered that it's a regression in llvm(-config). On e.g. debian it is included in llvm-config, and if I download the Arch package for the same llvm version it also outputs -lffi there, so seems to have been a regression between LLVM 3.5 and 3.9. Would need help from some LLVM people to figure out what changed though.

[cuviper]

I noticed Fedora is using --disable-rustbuild http://pkgs.fedoraproject.org/cgit/rpms/rust.git/tree/rust.spec#n260 which retains the old behavior.

For 1.15, yes, as I haven't transitioned yet. I hope to use rustbuild for 1.16.

Fedora doesn't normally use static linking, but it's an option, and you can see my ffi workaround here:
http://pkgs.fedoraproject.org/cgit/rpms/rust.git/tree/rust.spec#n233

I still think llvm-config --link-static --system-libs ought to output -lffi itself though. It was mentioned in #34486 (comment) that llvm-config has a FIXME about this, which is still there in the latest sources.

[Mark-Simulacrum]

I take it this isn't a problem on Rust's side, so closing. If I'm wrong please let us know!

[tmccombs]

is there an llvm issue open for this?