Auto merge of #1243 - RalfJung:instant, r=RalfJung

implement Instant::now

For now, this is Linux-only.

Unlike `SystemTime`, we cannot convert `Instant` to something absolute via an epoch. But that's okay, that clock is relative anyway, so we just make up our own time anchor when interpretation starts.

Fixes https://github.com/rust-lang/miri/issues/1242

src/machine.rs

@@ -5,6 +5,7 @@ use std::borrow::Cow;
 use std::cell::RefCell;
 use std::num::NonZeroU64;
 use std::rc::Rc;
+use std::time::Instant;
 
 use rand::rngs::StdRng;
 
@@ -164,6 +165,9 @@ pub struct Evaluator<'tcx> {
     /// the call to `miri_start_panic` (the panic payload) when unwinding.
     /// This is pointer-sized, and matches the `Payload` type in `src/libpanic_unwind/miri.rs`.
     pub(crate) panic_payload: Option<Scalar<Tag>>,
+
+    /// The "time anchor" for this machine's monotone clock (for `Instant` simulation).
+    pub(crate) time_anchor: Instant,
 }
 
 impl<'tcx> Evaluator<'tcx> {
@@ -182,6 +186,7 @@ impl<'tcx> Evaluator<'tcx> {
             file_handler: Default::default(),
             dir_handler: Default::default(),
             panic_payload: None,
+            time_anchor: Instant::now(),
         }
     }
 }

src/shims/foreign_items/posix/macos.rs

@@ -66,6 +66,10 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 let result = this.gettimeofday(args[0], args[1])?;
                 this.write_scalar(Scalar::from_int(result, dest.layout.size), dest)?;
             }
+            "mach_absolute_time" => {
+                let result = this.mach_absolute_time()?;
+                this.write_scalar(Scalar::from_uint(result, dest.layout.size), dest)?;
+            }
 
             // Other shims
             "pthread_attr_get_np" => {

src/shims/fs.rs

@@ -574,8 +574,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         buf_op: OpTy<'tcx, Tag>,
     ) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
-        this.check_no_isolation("stat")?;
         this.assert_platform("macos", "stat");
+        this.check_no_isolation("stat")?;
         // `stat` always follows symlinks.
         this.macos_stat_or_lstat(true, path_op, buf_op)
     }
@@ -587,8 +587,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         buf_op: OpTy<'tcx, Tag>,
     ) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
-        this.check_no_isolation("lstat")?;
         this.assert_platform("macos", "lstat");
+        this.check_no_isolation("lstat")?;
         this.macos_stat_or_lstat(false, path_op, buf_op)
     }
 
@@ -599,8 +599,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
     ) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
 
-        this.check_no_isolation("fstat")?;
         this.assert_platform("macos", "fstat");
+        this.check_no_isolation("fstat")?;
 
         let fd = this.read_scalar(fd_op)?.to_i32()?;
 
@@ -621,8 +621,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
     ) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
 
-        this.check_no_isolation("statx")?;
         this.assert_platform("linux", "statx");
+        this.check_no_isolation("statx")?;
 
         let statxbuf_scalar = this.read_scalar(statxbuf_op)?.not_undef()?;
         let pathname_scalar = this.read_scalar(pathname_op)?.not_undef()?;
@@ -880,8 +880,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
     ) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
 
-        this.check_no_isolation("readdir64_r")?;
         this.assert_platform("linux", "readdir64_r");
+        this.check_no_isolation("readdir64_r")?;
 
         let dirp = this.read_scalar(dirp_op)?.to_machine_usize(this)?;
 
@@ -967,8 +967,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
     ) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
 
-        this.check_no_isolation("readdir_r")?;
         this.assert_platform("macos", "readdir_r");
+        this.check_no_isolation("readdir_r")?;
 
         let dirp = this.read_scalar(dirp_op)?.to_machine_usize(this)?;
 

src/shims/time.rs

@@ -1,14 +1,10 @@
-use std::time::{Duration, SystemTime};
+use std::time::{Duration, SystemTime, Instant};
+use std::convert::TryFrom;
 
 use crate::stacked_borrows::Tag;
 use crate::*;
 use helpers::immty_from_int_checked;
 
-// Returns the time elapsed between now and the unix epoch as a `Duration`.
-fn get_time<'tcx>() -> InterpResult<'tcx, Duration> {
-    system_time_to_duration(&SystemTime::now())
-}
-
 /// Returns the time elapsed between the provided time and the unix epoch as a `Duration`.
 pub fn system_time_to_duration<'tcx>(time: &SystemTime) -> InterpResult<'tcx, Duration> {
     time.duration_since(SystemTime::UNIX_EPOCH)
@@ -17,7 +13,6 @@ pub fn system_time_to_duration<'tcx>(time: &SystemTime) -> InterpResult<'tcx, Du
 
 impl<'mir, 'tcx> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
-    // Foreign function used by linux
     fn clock_gettime(
         &mut self,
         clk_id_op: OpTy<'tcx, Tag>,
@@ -25,18 +20,24 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
     ) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
 
+        this.assert_platform("linux", "clock_gettime");
         this.check_no_isolation("clock_gettime")?;
 
         let clk_id = this.read_scalar(clk_id_op)?.to_i32()?;
-        if clk_id != this.eval_libc_i32("CLOCK_REALTIME")? {
+        let tp = this.deref_operand(tp_op)?;
+
+        let duration = if clk_id == this.eval_libc_i32("CLOCK_REALTIME")? {
+            system_time_to_duration(&SystemTime::now())?
+        } else if clk_id == this.eval_libc_i32("CLOCK_MONOTONIC")? {
+            // Absolute time does not matter, only relative time does, so we can just
+            // use our own time anchor here.
+            Instant::now().duration_since(this.machine.time_anchor)
+        } else {
             let einval = this.eval_libc("EINVAL")?;
             this.set_last_error(einval)?;
             return Ok(-1);
-        }
+        };
 
-        let tp = this.deref_operand(tp_op)?;
-
-        let duration = get_time()?;
         let tv_sec = duration.as_secs();
         let tv_nsec = duration.subsec_nanos();
 
@@ -49,7 +50,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
         Ok(0)
     }
-    // Foreign function used by generic unix (in particular macOS)
+
     fn gettimeofday(
         &mut self,
         tv_op: OpTy<'tcx, Tag>,
@@ -57,7 +58,9 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
     ) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
 
+        this.assert_platform("macos", "gettimeofday");
         this.check_no_isolation("gettimeofday")?;
+
         // Using tz is obsolete and should always be null
         let tz = this.read_scalar(tz_op)?.not_undef()?;
         if !this.is_null(tz)? {
@@ -68,7 +71,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
         let tv = this.deref_operand(tv_op)?;
 
-        let duration = get_time()?;
+        let duration = system_time_to_duration(&SystemTime::now())?;
         let tv_sec = duration.as_secs();
         let tv_usec = duration.subsec_micros();
 
@@ -81,4 +84,17 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
         Ok(0)
     }
+
+    fn mach_absolute_time(&self) -> InterpResult<'tcx, u64> {
+        let this = self.eval_context_ref();
+
+        this.assert_platform("macos", "mach_absolute_time");
+        this.check_no_isolation("mach_absolute_time")?;
+
+        // This returns a u64, with time units determined dynamically by `mach_timebase_info`.
+        // We return plain nanoseconds.
+        let duration = Instant::now().duration_since(this.machine.time_anchor);
+        u64::try_from(duration.as_nanos())
+            .map_err(|_| err_unsup_format!("programs running longer than 2^64 nanoseconds are not supported").into())
+    }
 }

tests/run-pass/clock.rs

@@ -1,14 +0,0 @@
-// ignore-windows: TODO clock shims are not implemented on Windows
-// compile-flags: -Zmiri-disable-isolation
-
-use std::time::SystemTime;
-
-fn main() {
-   let now1 = SystemTime::now();
-
-    // Do some work to make time pass.
-    for _ in 0..10 { drop(vec![42]); }
-
-   let now2 = SystemTime::now();
-   assert!(now2 > now1);
-}

tests/run-pass/time.rs

@@ -0,0 +1,18 @@
+// ignore-windows: TODO clock shims are not implemented on Windows
+// compile-flags: -Zmiri-disable-isolation
+
+use std::time::{SystemTime, Instant};
+
+fn main() {
+    let now1 = SystemTime::now();
+    // Do some work to make time pass.
+    for _ in 0..10 { drop(vec![42]); }
+    let now2 = SystemTime::now();
+    assert!(now2 > now1);
+
+    let now1 = Instant::now();
+    // Do some work to make time pass.
+    for _ in 0..10 { drop(vec![42]); }
+    let now2 = Instant::now();
+    assert!(now2 > now1);
+}