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use CLOCK_BOOTTIME in Instant::now #88714

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use CLOCK_BOOTTIME in Instant::now #88714

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3ab376d
use CLOCK_BOOTTIME in Instant::now
hellow554 Nov 29, 2022
2ab523d
add CLOCK_BOOTTIME to miri shims
hellow554 Nov 30, 2022
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3 changes: 3 additions & 0 deletions src/tools/miri/src/shims/time.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,9 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
relative_clocks = vec![
this.eval_libc_i32("CLOCK_MONOTONIC")?,
this.eval_libc_i32("CLOCK_MONOTONIC_COARSE")?,
// This is the equivalent to `CLOCK_UPTIME_RAW` in the macos section
// We support it, because std relies on it
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@RalfJung RalfJung Nov 30, 2022 •
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This comment is backwards -- BOOTTIME you say does increment when the machine is asleep, but CLOCK_UPTIME_RAW does not.

If anything, it seems like CLOCK_BOOTTIME on linux is like CLOCK_MONOTONIC on macOS, and CLOCK_MONOTONIC on linux is like CLOCK_UPTIME_RAW (and mach_absolute_time) on macos?

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Yeah judging from a quick search, looks like MONOTONIC on Linux does not increment when sleeping, but on macos it does. It also looks before this PR we are actually consistent (both Linux and macos use clocks that do not count when the system is asleep), and this PR makes us inconsistent by changing only Linux.

Or maybe I am looking at the wrong docs? This seems to look reasonably official though for macos.

Comment on lines +48 to +49
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@RalfJung RalfJung Nov 30, 2022 •
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Suggested change
// This is the equivalent to `CLOCK_UPTIME_RAW` in the macos section
// We support it, because std relies on it
// Unlike `CLOCK_MONOTONIC` (which is weird on Linux in that it does not increment
// during system sleep), this *is* supposed to increment during system sleep...
// but that's not really something a program running inside Miri can tell, anyway.
// We support it because std relies on it.

this.eval_libc_i32("CLOCK_BOOTTIME")?,
];
}
"macos" => {
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