make Miri's scheduler proper round-robin
When thread N blocks or yields, we activate thread N+1 next, rather than always activating thread 0. This should guarantee that as long as all threads regularly yield, each thread eventually takes a step again.
Fixes the "multiple loops that yield playing ping-pong" part of https://github.com/rust-lang/miri/issues/1388.
`@cbeuw` I hope this doesn't screw up the scheduler-dependent tests you are adding in your PR.
ui_test tweaks
- support multiple filters
- make `./miri check` also cover ui_test
- Run opt-level=4 tests again, but only the "run" tests
r? `@oli-obk`
Save a created event for zero-size reborrows
Currently, we don't save a created event for zero-sized reborrows. Attempting to use something from a zero-sized reborrow is surprisingly common, for example on `minimal-lexical==0.2.1` we previously just emit this:
```
Undefined Behavior: attempting a write access using <187021> at alloc72933[0x0], but that tag does not exist in the borrow stack for this location
--> /root/rust/library/core/src/ptr/mod.rs:1287:9
|
1287 | copy_nonoverlapping(&src as *const T, dst, 1);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| |
| attempting a write access using <187021> at alloc72933[0x0], but that tag does not exist in the borrow stack for this location
| this error occurs as part of an access at alloc72933[0x0..0x8]
|
= help: this indicates a potential bug in the program: it performed an invalid operation, but the rules it violated are still experimental
= help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
= note: inside `std::ptr::write::<u64>` at /root/rust/library/core/src/ptr/mod.rs:1287:9
note: inside `minimal_lexical::stackvec::StackVec::push_unchecked` at /root/build/src/stackvec.rs:82:13
--> /root/build/src/stackvec.rs:82:13
|
82 | ptr::write(self.as_mut_ptr().add(self.len()), value);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
... backtrace continues...
```
Which leaves us with the question "where did we make this pointer?" because for every other diagnostic you get a "was created by" note, so I suspect people might be tempted to think there is a Miri bug here. I certainly was.
---
This code duplication is so awful, I'm going to take a look at cleaning it up later. The fact that `ptr_get_alloc_id` can fail in this situation makes things annoying.
Add support for _COARSE clocks
Original idea does not work, so I'm just going to try expanding support to include the `_COARSE` clocks.
The original motivation for this PR is that the test suite for the crate [`minstant`](https://crates.io/crates/minstant) reports UB, because it tries to use a clock type Miri didn't support, but never checked for an error code and so just used the uninit `libc::timespec`. So, that's technically a bug in `minstant`, but outside of Miri you'd have to be using an incredibly old Linux to ever see an `EINVAL` so the more helpful thing for Miri to do is behave like a newer Linux.
So now we don't detect UB in `minstant`, but we have a test failure:
```
failures:
---- src/instant.rs - instant::Instant::as_unix_nanos (line 150) stdout ----
Test executable failed (exit status: 101).
stderr:
thread 'main' panicked at 'assertion failed: (instant.as_unix_nanos(&anchor) as i64 - expected as i64).abs() < 1_000_000', src/instant.rs:11:1
```
I'm having trouble getting my head around the code in `minstant` that's involved in this test, but as far as I can tell from the man pages, these `_COARSE` clocks meet the requirements.
Closes https://github.com/rust-lang/miri/issues/1983 at least as best as I can.
