macOS: cannot subtract Instants (mach_timebase_info not implemented)

[RalfJung]

On macOS, we cannot subtract one Instant from another:

error: unsupported operation: can't call foreign function: mach_timebase_info
   --> /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/sys/unix/time.rs:239:13
    |
239 |             mach_timebase_info(&mut info);
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ can't call foreign function: mach_timebase_info
    |
    = help: this is likely not a bug in the program; it indicates that the program performed an operation that the interpreter does not support
    = note: inside call to `std::sys::unix::time::inner::info` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/sys/unix/time.rs:156:24
    = note: inside call to `std::sys::unix::time::inner::Instant::checked_sub_instant` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/time.rs:263:9
note: inside call to `std::time::Instant::duration_since` at tests/run-pass/time.rs:25:20
   --> tests/run-pass/time.rs:25:20
    |
25  |         let diff = now2.duration_since(now1);
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: inside call to `main` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/rt.rs:67:34

[samrat]

I am unable to reproduce this on macOS 10.14.6-- all tests pass when I run ./miri test on commit 4545eff.

[RalfJung]

@samrat yes they should pass, we have CI for that. :)
But this feature is not implemented yet, so we are also not testing it on macOS. If you want to test it locally, edit this file to remove the #[cfg(not(target_os = "macos"))], then run

./miri run tests/run-pass/time.rs -Zmiri-disable-isolation

[samrat]

Ah, yes I am able to reproduce this now-- I thought it might have gotten fixed since this issue was created.

I am quite new to the miri codebase but I'll try to come up with a fix for this issue.

[RalfJung]

Sure, let me know if you need any help. :)