Auto merge of #975 - christianpoveda:clock-shim, r=RalfJung

Add clock_gettime shim

r? @oli-obk

I think there is no way to do proper testing of this other than checking that miri does not crash when calling `clock_gettime`.

src/helpers.rs

@@ -1,8 +1,11 @@
 use std::mem;
 
-use rustc::ty::{self, layout::{self, Size, Align}};
 use rustc::hir::def_id::{DefId, CRATE_DEF_INDEX};
 use rustc::mir;
+use rustc::ty::{
+    self,
+    layout::{self, Align, LayoutOf, Size, TyLayout},
+};
 
 use rand::RngCore;
 
@@ -304,4 +307,36 @@ fn eval_libc(&mut self, name: &str) -> InterpResult<'tcx, Scalar<Tag>> {
     fn eval_libc_i32(&mut self, name: &str) -> InterpResult<'tcx, i32> {
         self.eval_libc(name)?.to_i32()
     }
+
+    /// Helper function to get the `TyLayout` of a `libc` type
+    fn libc_ty_layout(&mut self, name: &str) -> InterpResult<'tcx, TyLayout<'tcx>> {
+        let this = self.eval_context_mut();
+        let tcx = &{ this.tcx.tcx };
+        let ty = this.resolve_path(&["libc", name])?.ty(*tcx);
+        this.layout_of(ty)
+    }
+
+    // Writes several `ImmTy`s contiguosly into memory. This is useful when you have to pack
+    // different values into a struct.
+    fn write_packed_immediates(
+        &mut self,
+        place: &MPlaceTy<'tcx, Tag>,
+        imms: &[ImmTy<'tcx, Tag>],
+    ) -> InterpResult<'tcx> {
+        let this = self.eval_context_mut();
+
+        let tcx = &{ this.tcx.tcx };
+
+        let mut offset = Size::from_bytes(0);
+
+        for &imm in imms {
+            this.write_immediate_to_mplace(
+                *imm,
+                place.offset(offset, None, imm.layout, tcx)?,
+            )?;
+            offset += imm.layout.size;
+        }
+
+        Ok(())
+    }
 }

src/lib.rs

@@ -32,6 +32,7 @@
 pub use crate::shims::foreign_items::EvalContextExt as ForeignItemsEvalContextExt;
 pub use crate::shims::intrinsics::EvalContextExt as IntrinsicsEvalContextExt;
 pub use crate::shims::tls::{EvalContextExt as TlsEvalContextExt, TlsData};
+pub use crate::shims::time::{EvalContextExt as TimeEvalContextExt};
 pub use crate::shims::dlsym::{Dlsym, EvalContextExt as DlsymEvalContextExt};
 pub use crate::shims::env::{EnvVars, EvalContextExt as EnvEvalContextExt};
 pub use crate::shims::fs::{FileHandler, EvalContextExt as FileEvalContextExt};

src/shims/foreign_items.rs

@@ -507,6 +507,16 @@ fn emulate_foreign_item(
                 this.write_scalar(Scalar::from_int(result, dest.layout.size), dest)?;
             }
 
+            "clock_gettime" => {
+                let result = this.clock_gettime(args[0], args[1])?;
+                this.write_scalar(Scalar::from_int(result, dest.layout.size), dest)?;
+            }
+
+            "gettimeofday" => {
+                let result = this.gettimeofday(args[0], args[1])?;
+                this.write_scalar(Scalar::from_int(result, dest.layout.size), dest)?;
+            }
+
             "strlen" => {
                 let ptr = this.read_scalar(args[0])?.not_undef()?;
                 let n = this.memory().read_c_str(ptr)?.len();

src/shims/mod.rs

@@ -4,6 +4,7 @@
 pub mod intrinsics;
 pub mod tls;
 pub mod fs;
+pub mod time;
 
 use rustc::{mir, ty};
 

src/shims/time.rs

@@ -0,0 +1,104 @@
+use std::time::{Duration, SystemTime};
+
+use rustc::ty::layout::TyLayout;
+
+use crate::stacked_borrows::Tag;
+use crate::*;
+
+// Returns the time elapsed between now and the unix epoch as a `Duration` and the sign of the time
+// interval
+fn get_time<'tcx>() -> InterpResult<'tcx, Duration> {
+    SystemTime::now()
+        .duration_since(SystemTime::UNIX_EPOCH)
+        .map_err(|_| err_unsup_format!("Times before the Unix epoch are not supported").into())
+}
+
+fn int_to_immty_checked<'tcx>(
+    int: i128,
+    layout: TyLayout<'tcx>,
+) -> InterpResult<'tcx, ImmTy<'tcx, Tag>> {
+    // If `int` does not fit in `size` bits, we error instead of letting
+    // `ImmTy::from_int` panic.
+    let size = layout.size;
+    let truncated = truncate(int as u128, size);
+    if sign_extend(truncated, size) as i128 != int {
+        throw_unsup_format!(
+            "Signed value {:#x} does not fit in {} bits",
+            int,
+            size.bits()
+        )
+    }
+    Ok(ImmTy::from_int(int, layout))
+}
+
+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>,
+        tp_op: OpTy<'tcx, Tag>,
+    ) -> InterpResult<'tcx, i32> {
+        let this = self.eval_context_mut();
+
+        if !this.machine.communicate {
+            throw_unsup_format!("`clock_gettime` not available when isolation is enabled")
+        }
+
+        let clk_id = this.read_scalar(clk_id_op)?.to_i32()?;
+        if clk_id != this.eval_libc_i32("CLOCK_REALTIME")? {
+            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() as i128;
+        let tv_nsec = duration.subsec_nanos() as i128;
+
+        let imms = [
+            int_to_immty_checked(tv_sec, this.libc_ty_layout("time_t")?)?,
+            int_to_immty_checked(tv_nsec, this.libc_ty_layout("c_long")?)?,
+        ];
+
+        this.write_packed_immediates(&tp, &imms)?;
+
+        Ok(0)
+    }
+    // Foreign function used by generic unix (in particular macOS)
+    fn gettimeofday(
+        &mut self,
+        tv_op: OpTy<'tcx, Tag>,
+        tz_op: OpTy<'tcx, Tag>,
+    ) -> InterpResult<'tcx, i32> {
+        let this = self.eval_context_mut();
+
+        if !this.machine.communicate {
+            throw_unsup_format!("`gettimeofday` not available when isolation is enabled")
+        }
+        // Using tz is obsolete and should always be null
+        let tz = this.read_scalar(tz_op)?.not_undef()?;
+        if !this.is_null(tz)? {
+            let einval = this.eval_libc("EINVAL")?;
+            this.set_last_error(einval)?;
+            return Ok(-1);
+        }
+
+        let tv = this.deref_operand(tv_op)?;
+
+        let duration = get_time()?;
+        let tv_sec = duration.as_secs() as i128;
+        let tv_usec = duration.subsec_micros() as i128;
+
+        let imms = [
+            int_to_immty_checked(tv_sec, this.libc_ty_layout("time_t")?)?,
+            int_to_immty_checked(tv_usec, this.libc_ty_layout("suseconds_t")?)?,
+        ];
+
+        this.write_packed_immediates(&tv, &imms)?;
+
+        Ok(0)
+    }
+}

tests/run-pass/clock.rs

@@ -0,0 +1,8 @@
+// ignore-windows: TODO clock shims are not implemented on Windows
+// compile-flags: -Zmiri-disable-isolation
+
+use std::time::SystemTime;
+
+fn main() {
+   let _now = SystemTime::now();
+}