rustc should attempt to use the gold linker by default, but this breaks Debian Wheezy because of obsolete gcc

[brson]

Original report.

Rust nightly uses the gold linker where it can by passing -fuse-ld=gold to gcc when it sees that ld.gold exists. Unfortunately, even if ld.gold exists gcc may not understand -fuse-ld=gold.

This distro came out in May 2013, so it's not that old.

[brson]

If this can't be fixed in the next week it should probably be reverted to rethink the migration strategy.

[alexcrichton]

Aw man this is unfortunate. Agree on reverting if we can't figure anything else out.

I guess an "ideal solution" would be if gcc/clang read an environment variable as well as an argument, but I unfortunately don't see such an environment variable in clang at least. We can maybe try to parse something like /etc/issue but that seems pretty sketchy.

I wonder, how is one supposed to tell gcc on wheezy to use gold?

[brson]

@xitep suggested how to detect gcc's support for this. Unfortunately it involves running gcc an extra time. I can't think of anything better.

[alexcrichton]

It's true that's a possibility, I would likely prefer to see that as the compiler attempts to run the entire linker and then parses the error message if one shows up, and only then is gold removed if the entire linker fails. That way we'd only run gcc once if possible, and twice in the worst case.

That being said that's still a pretty big hit for distros because it's 2 times on all compiles, which is pretty unfortunate :(

[xitep]

I actually like the idea of environment variables from a user perspective. If I'd be able to set RUSTC_DISABLE_GOLD=1 (or similar) in one of my login scripts to the system I'd be totally happy (right now my solution is quite ugly with wrapping rustc with custom scripts). So far, I think, rustc itself doesn't interpret any envs, does it? So it'd be new territory with its own set of problems I guess.

[alexcrichton]

Oh sorry I meant moreso the compiler sets an environment variable which gcc then interprets rather than the other way around. I'd personally prefer to avoid too many environment variables for the rustc compiler.

[xitep]

"I wonder, how is one supposed to tell gcc on wheezy to use gold?": it seems just by installing binutils-gold. /usr/bin/ld becomes a symlink to /usr/bin/ld.gold.

[xitep]

An alternative to /etc/issue might also be /etc/debian_version. But using these files seems very fragile to me :/ And adding dependencies on such external files will probably make the code in rustc unmaintainable in some future.

[alexcrichton]

Hm detecting whether ld is a symlink and whether it points to ld.gold seems reasonable, but there's still a possibility that the symlink isn't there, ld.gold exists, and -fuse-ld=gold isn't accepted unfortunately

[pnkfelix]

@alexcrichton

That being said that's still a pretty big hit for distros because it's 2 times on all compiles, which is pretty unfortunate

Assuming we add some way for the user to specify "disable gold", we could issue a warning when we run gcc twice, recommending that the user change their rustc invocation (or host configuration) accordingly

[pnkfelix]

(that way it's only "2 times until user changes host configuration to disable gold usage on rustc " Which is better than 2 times always

[alexcrichton]

@pnkfelix perhaps yeah, but at that point I'd probably be more in favor of just disabling by default.