time: use clock_gettime on all unixen

This retires gettimeofday in favor of clock_gettime(CLOCK_REALTIME) on:

```
    all(target_os = "macos", not(target_arch = "aarch64")),
    target_os = "ios",
    target_os = "watchos",
    target_os = "tvos"
))]
```

gettimeofday was first used in
time-rs/time@cc367ed
which predated the introduction of clock_gettime support in macOS 10.12
Sierra. As of 58bbca9, this is the
minimum supported version.

library/std/src/sys/unix/time.rs

@@ -40,6 +40,10 @@ impl SystemTime {
         SystemTime { t: Timespec::new(tv_sec, tv_nsec) }
     }
 
+    pub fn now() -> SystemTime {
+        SystemTime { t: Timespec::now(libc::CLOCK_REALTIME) }
+    }
+
     pub fn sub_time(&self, other: &SystemTime) -> Result<Duration, Duration> {
         self.t.sub_timespec(&other.t)
     }
@@ -79,6 +83,36 @@ impl Timespec {
         Timespec { tv_sec, tv_nsec: unsafe { Nanoseconds(tv_nsec as u32) } }
     }
 
+    pub fn now(clock: libc::clockid_t) -> Timespec {
+        use crate::mem::MaybeUninit;
+        use crate::sys::cvt;
+
+        // Try to use 64-bit time in preparation for Y2038.
+        #[cfg(all(
+            target_os = "linux",
+            target_env = "gnu",
+            target_pointer_width = "32",
+            not(target_arch = "riscv32")
+        ))]
+        {
+            use crate::sys::weak::weak;
+
+            // __clock_gettime64 was added to 32-bit arches in glibc 2.34,
+            // and it handles both vDSO calls and ENOSYS fallbacks itself.
+            weak!(fn __clock_gettime64(libc::clockid_t, *mut super::__timespec64) -> libc::c_int);
+
+            if let Some(clock_gettime64) = __clock_gettime64.get() {
+                let mut t = MaybeUninit::uninit();
+                cvt(unsafe { clock_gettime64(clock, t.as_mut_ptr()) }).unwrap();
+                return Timespec::from(unsafe { t.assume_init() });
+            }
+        }
+
+        let mut t = MaybeUninit::uninit();
+        cvt(unsafe { libc::clock_gettime(clock, t.as_mut_ptr()) }).unwrap();
+        Timespec::from(unsafe { t.assume_init() })
+    }
+
     pub fn sub_timespec(&self, other: &Timespec) -> Result<Duration, Duration> {
         if self >= other {
             // NOTE(eddyb) two aspects of this `if`-`else` are required for LLVM
@@ -224,7 +258,6 @@ impl From<__timespec64> for Timespec {
 ))]
 mod inner {
     use crate::sync::atomic::{AtomicU64, Ordering};
-    use crate::sys::cvt;
     use crate::sys_common::mul_div_u64;
     use crate::time::Duration;
 
@@ -268,16 +301,6 @@ mod inner {
         }
     }
 
-    impl SystemTime {
-        pub fn now() -> SystemTime {
-            use crate::ptr;
-
-            let mut s = libc::timeval { tv_sec: 0, tv_usec: 0 };
-            cvt(unsafe { libc::gettimeofday(&mut s, ptr::null_mut()) }).unwrap();
-            return SystemTime::from(s);
-        }
-    }
-
     impl From<libc::timeval> for Timespec {
         fn from(t: libc::timeval) -> Timespec {
             Timespec::new(t.tv_sec as i64, 1000 * t.tv_usec as i64)
@@ -345,11 +368,9 @@ mod inner {
 )))]
 mod inner {
     use crate::fmt;
-    use crate::mem::MaybeUninit;
-    use crate::sys::cvt;
     use crate::time::Duration;
 
-    use super::{SystemTime, Timespec};
+    use super::Timespec;
 
     #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
     pub struct Instant {
@@ -386,39 +407,4 @@ mod inner {
                 .finish()
         }
     }
-
-    impl SystemTime {
-        pub fn now() -> SystemTime {
-            SystemTime { t: Timespec::now(libc::CLOCK_REALTIME) }
-        }
-    }
-
-    impl Timespec {
-        pub fn now(clock: libc::clockid_t) -> Timespec {
-            // Try to use 64-bit time in preparation for Y2038.
-            #[cfg(all(
-                target_os = "linux",
-                target_env = "gnu",
-                target_pointer_width = "32",
-                not(target_arch = "riscv32")
-            ))]
-            {
-                use crate::sys::weak::weak;
-
-                // __clock_gettime64 was added to 32-bit arches in glibc 2.34,
-                // and it handles both vDSO calls and ENOSYS fallbacks itself.
-                weak!(fn __clock_gettime64(libc::clockid_t, *mut super::__timespec64) -> libc::c_int);
-
-                if let Some(clock_gettime64) = __clock_gettime64.get() {
-                    let mut t = MaybeUninit::uninit();
-                    cvt(unsafe { clock_gettime64(clock, t.as_mut_ptr()) }).unwrap();
-                    return Timespec::from(unsafe { t.assume_init() });
-                }
-            }
-
-            let mut t = MaybeUninit::uninit();
-            cvt(unsafe { libc::clock_gettime(clock, t.as_mut_ptr()) }).unwrap();
-            Timespec::from(unsafe { t.assume_init() })
-        }
-    }
 }

library/std/src/time.rs

@@ -221,7 +221,7 @@ pub struct Instant(time::Instant);
 /// |-----------|----------------------------------------------------------------------|
 /// | SGX       | [`insecure_time` usercall]. More information on [timekeeping in SGX] |
 /// | UNIX      | [clock_gettime (Realtime Clock)]                                     |
-/// | Darwin    | [gettimeofday]                                                       |
+/// | Darwin    | [clock_gettime (Realtime Clock)]                                     |
 /// | VXWorks   | [clock_gettime (Realtime Clock)]                                     |
 /// | SOLID     | `SOLID_RTC_ReadTime`                                                 |
 /// | WASI      | [__wasi_clock_time_get (Realtime Clock)]                             |
@@ -230,7 +230,6 @@ pub struct Instant(time::Instant);
 /// [currently]: crate::io#platform-specific-behavior
 /// [`insecure_time` usercall]: https://edp.fortanix.com/docs/api/fortanix_sgx_abi/struct.Usercalls.html#method.insecure_time
 /// [timekeeping in SGX]: https://edp.fortanix.com/docs/concepts/rust-std/#codestdtimecode
-/// [gettimeofday]: https://man7.org/linux/man-pages/man2/gettimeofday.2.html
 /// [clock_gettime (Realtime Clock)]: https://linux.die.net/man/3/clock_gettime
 /// [__wasi_clock_time_get (Realtime Clock)]: https://github.com/WebAssembly/WASI/blob/main/legacy/preview1/docs.md#clock_time_get
 /// [GetSystemTimePreciseAsFileTime]: https://docs.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getsystemtimepreciseasfiletime