Allow backtraces to cross thread boundaries

[actuallyatoaster]

Fixes #4066

When a thread is spawned we store the ID of the spawning thread as well as a backtrace to the spawn location. When there's an error we can traverse upwards, displaying a backtrace up to the main thread.

For instance, with the following program:

extern "C" {
    fn unknown();
}

fn bad() {
    unsafe { unknown() }
}

fn main() {
    std::thread::spawn(bad);
}

Whereas previously we would see:

error: unsupported operation: can't call foreign function `unknown` on OS `linux`
 --> tests/temp.rs:6:14
  |
6 |     unsafe { unknown() }
  |              ^^^^^^^^^ can't call foreign function `unknown` on OS `linux`
  |
  = help: if this is a basic API commonly used on this target, please report an issue with Miri
  = help: however, note that Miri does not aim to support every FFI function out there; for instance, we will not support APIs for things such as GUIs, scripting languages, or databases
  = note: BACKTRACE on thread `unnamed-1`:
  = note: inside `bad` at tests/temp.rs:6:14: 6:23

note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

error: aborting due to 1 previous error

We now have:

error: unsupported operation: can't call foreign function `unknown` on OS `linux`
  --> tests/temp.rs:6:14
   |
6  |     unsafe { unknown() }
   |              ^^^^^^^^^ can't call foreign function `unknown` on OS `linux`
   |
   = help: if this is a basic API commonly used on this target, please report an issue with Miri
   = help: however, note that Miri does not aim to support every FFI function out there; for instance, we will not support APIs for things such as GUIs, scripting languages, or databases
   = note: BACKTRACE on thread `unnamed-1`:
   = note: inside `bad` at tests/temp.rs:6:14: 6:23
   = note: thread `unnamed-1` was spawned by thread `main`
   = note: inside `std::sys::pal::unix::thread::Thread::new` at /home/reimu/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/sys/pal/unix/thread.rs:84:19: 84:86
   = note: inside `std::thread::Builder::spawn_unchecked_::<'_, fn() {bad}, ()>` at /home/reimu/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/thread/mod.rs:600:30: 600:64
   = note: inside `std::thread::Builder::spawn_unchecked::<fn() {bad}, ()>` at /home/reimu/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/thread/mod.rs:467:32: 467:62
   = note: inside `std::thread::Builder::spawn::<fn() {bad}, ()>` at /home/reimu/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/thread/mod.rs:400:18: 400:41
   = note: inside `std::thread::spawn::<fn() {bad}, ()>` at /home/reimu/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/thread/mod.rs:730:5: 730:28
note: inside `main`
  --> tests/temp.rs:10:5
   |
10 |     std::thread::spawn(bad);
   |     ^^^^^^^^^^^^^^^^^^^^^^^

note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

error: aborting due to 1 previous error

[oli-obk]

You'll need to bless the windows tests, too. It should suffice to pass --target with a windows target, no windows host needed

[RalfJung]

I have some nits.

[RalfJung]

@rustbot author Please post @rustbot ready when the PR is ready for the next round of review.

[rustbot]

:umbrella: The latest upstream changes (possibly 807129cf8228252494eb074a1df13f5decb0c78b) made this pull request unmergeable. Please resolve the merge conflicts.

[RalfJung]

I will close this due to inactivity. Feel free to reopen if you want to pick this back up!