Fix link error with #[thread_local] introduced by #71192

[Amanieu]

r? @oli-obk

[oli-obk]

@bors r+

Nominating for beta backport because the bug carried over to beta and while I'm not sure if it's exploitable without feature gates, I'd rather not take the risk.

[bors]

📌 Commit e9b67d2 has been approved by oli-obk

[RalfJung]

So what was the problem here? Did some component "forget" to look into usize to check for things to link against? The fix doesn't have anything to do with usize though so I must be missing something.

[oli-obk]

@bors r-

I just noticed that the regression test also passes on nightly, so it's not really testing the problem being fixed here.

[Amanieu]

It still fails on the latest nightly for me. Make sure you're compiling with optimizations enabled and with multiple codegen units.

[oli-obk]

Since the test neither specifies optimizations nor CGU, it won't test this in CI. Just turning on optimizations in the playground doesn't work: https://play.rust-lang.org/?version=nightly&mode=release&edition=2018&gist=95fdf2822783b106f65757321e6ce187

Can you add your command line flags to the test via a // compile-flags: foo comment?

[Amanieu]

I can reproduce the error with just rustc tls.rs -O.

[oli-obk]

@bors r+

[bors]

📌 Commit 2af53e9 has been approved by oli-obk

[oli-obk]

So what was the problem here? Did some component "forget" to look into usize to check for things to link against? The fix doesn't have anything to do with usize though so I must be missing something.

usize is a red herring here. Casting to raw pointers would have sufficed. The cast is only there to work around the borrow checker and being able to compare addresses. If you were wondering whether the bug is because of a usize constant not being looked into, that's not a problem anymore as we don't support references to tls in const eval anymore.

The thing causing a bug here was simply that we didn't collect the DefId of the tls anymore, which randomly works in the tests we've had up to here, but was broken likely in cross crate and multi-cgu scenarios.

[tmiasko]

Failed in rollup #73299, on wasm32-unknown-unknown target without threads.

---- [ui] ui/tls.rs stdout ----

error: test run failed!
status: exit code: 101
command: "/node-v9.2.0-linux-x64/bin/node" "/checkout/src/etc/wasm32-shim.js" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/tls/a.wasm"
stdout:
------------------------------------------

------------------------------------------
stderr:
------------------------------------------
RuntimeError: unreachable
    at __rust_start_panic (wasm-function[89]:1)
    at rust_panic (wasm-function[83]:39)
    at _ZN3std9panicking20rust_panic_with_hook17h4caac20c72d75dc1E (wasm-function[78]:279)
    at rust_begin_unwind (wasm-function[77]:90)
    at _ZN4core9panicking9panic_fmt17h2a7f8c32bf7391a0E (wasm-function[108]:58)
    at _ZN4core6option18expect_none_failed17h300c1b4bc80874faE (wasm-function[118]:139)
    at _ZN3std6thread5spawn17hd38fc9ede2951672E (wasm-function[4]:407)
    at _ZN3tls4main17hfb802c933ee14077E (wasm-function[8]:25)
    at _ZN3std2rt10lang_start28_$u7b$$u7b$closure$u7d$$u7d$17h7dab73fdfb41bcd3E (wasm-function[10]:25)
    at _ZN3std10sys_common9backtrace28__rust_begin_short_backtrace17hee2c79df7781245bE (wasm-function[67]:8)
    at _ZN3std2rt19lang_start_internal17h5bcb99e6d909e866E (wasm-function[84]:229)
    at main (wasm-function[9]:46)
    at Object.<anonymous> (/checkout/src/etc/wasm32-shim.js:20:20)
    at Module._compile (module.js:641:30)
    at Object.Module._extensions..js (module.js:652:10)
    at Module.load (module.js:560:32)
    at tryModuleLoad (module.js:503:12)
    at Function.Module._load (module.js:495:3)
    at Function.Module.runMain (module.js:682:10)
    at startup (bootstrap_node.js:191:16)

------------------------------------------

Maybe build-pass would be sufficient to detect link error.

[spastorino]

This one is beta nominated so bumping the priority ...

@bors p=1

[bors]

⌛ Testing commit 01e29c7 with merge 5cbaf60ed01b7b1e19b34b258adfce40d8924827...

[bors]

💔 Test failed - checks-azure

[mati865]

Spurious failure:

##[error]We stopped hearing from agent Azure Pipelines 4. Verify the agent machine is running and has a healthy network connection. Anything that terminates an agent process, starves it for CPU, or blocks its network access can cause this error. For more information, see: https://go.microsoft.com/fwlink/?linkid=846610

[Amanieu]

@bors retry

[bors]

⌛ Testing commit 01e29c7 with merge 7d16c1d...

[bors]

☀️ Test successful - checks-azure
Approved by: oli-obk
Pushing 7d16c1d to master...

[pnkfelix]

Discussed in T-compiler meeting; beta approved.