intermittent sigsegv in text_util unit tests

[jdm]

http://build.servo.org/builders/mac-dev-unit/builds/11840/steps/test/logs/stdio

I've run the binary under a debugger and it appears to be a rustc problem, since it crashes in standard library code before actually running any test code.

[jdm]

FYI @KiChjang

[jdm]

This is https://github.com/servo/servo/blob/master/components/gfx/tests/text_util.rs

[mbrubeck]

This has happened at least four times (in builds from both #20754 and #20615). All the instances I've seen are from the same machine, servo-mac2. cc @edunham

[jdm]

I pulled the binary off of the machine and it continued to segfault. I'm not sure if that means anything.

[mbrubeck]

Maybe the rlib for one of the standard libraries on this machine is corrupt. Since it's statically linked to the binary, that would make the binary fail everywhere. We could try rustup toolchain uninstall nightly-2018-05-03 to force a re-install of the maybe-corrupt files.

[nox]

Seems like a perma failure to me.

[jdm]

This has now been observed on servo-mac4 as well (#20766 (comment)).

[highfive]

cc @aneeshusa

[jdm]

One possibility to work around this and allow merges to continue would be removing servo-mac2 and servo-mac4 from the pool of builders for mac-dev-unit at https://github.com/servo/saltfs/blob/master/buildbot/master/files/config/master.cfg#L178.

[jdm]

If the issue is nondeterministic codegen in rustc, we could try disabling codegen-units to see if it affects the output.

[jdm]

Observed on servo-mac7 as well (http://build.servo.org/builders/mac-dev-unit/builds/11897/steps/test/logs/stdio).

[jdm]

I can reproduce the exact same issue on servo-mac2 with the following testcase:

#[test]
fn foo() {}

and running rustc --test foo.rs. This appears with the 2018-05-14 nightly; it does not appear with the 2018-04-14 (our previous pinned rust version). I'm going to get a regression range and file a bug upstream; we should revert our last rustc update to allow our CI to make progress.

[jdm]

rust-lang/rust#50867