3 files changed, 55 insertions, 7 deletions
diff --git a/library/std/src/os/unix/net/tests.rs b/library/std/src/os/unix/net/tests.rs
index 3d4302e665c..6a6af9efd78 100644
--- a/library/std/src/os/unix/net/tests.rs
+++ b/library/std/src/os/unix/net/tests.rs
@@ -662,7 +662,7 @@ fn test_send_vectored_fds_unix_stream() {
     }
 }
 
-#[cfg(any(target_os = "android", target_os = "linux", target_os = "freebsd"))]
+#[cfg(any(target_os = "android", target_os = "linux"))]
 #[test]
 #[cfg_attr(target_os = "android", ignore)] // Android SELinux rules prevent creating Unix sockets
 fn test_send_vectored_with_ancillary_to_unix_datagram() {
diff --git a/library/std/src/panicking.rs b/library/std/src/panicking.rs
index 6ff7b19f293..b20e5464e6e 100644
--- a/library/std/src/panicking.rs
+++ b/library/std/src/panicking.rs
@@ -246,7 +246,9 @@ fn default_hook(info: &PanicInfo<'_>) {
 pub fn panic_hook_with_disk_dump(info: &PanicInfo<'_>, path: Option<&crate::path::Path>) {
     // If this is a double panic, make sure that we print a backtrace
     // for this panic. Otherwise only print it if logging is enabled.
-    let backtrace = if panic_count::get_count() >= 2 {
+    let backtrace = if info.force_no_backtrace() {
+        None
+    } else if panic_count::get_count() >= 2 {
         BacktraceStyle::full()
     } else {
         crate::panic::get_backtrace_style()
@@ -294,7 +296,7 @@ pub fn panic_hook_with_disk_dump(info: &PanicInfo<'_>, path: Option<&crate::path
                     }
                 }
             }
-            // If backtraces aren't supported, do nothing.
+            // If backtraces aren't supported or are forced-off, do nothing.
             None => {}
         }
     };
@@ -615,14 +617,23 @@ pub fn begin_panic_handler(info: &PanicInfo<'_>) -> ! {
     let loc = info.location().unwrap(); // The current implementation always returns Some
     let msg = info.message().unwrap(); // The current implementation always returns Some
     crate::sys_common::backtrace::__rust_end_short_backtrace(move || {
+        // FIXME: can we just pass `info` along rather than taking it apart here, only to have
+        // `rust_panic_with_hook` construct a new `PanicInfo`?
         if let Some(msg) = msg.as_str() {
-            rust_panic_with_hook(&mut StrPanicPayload(msg), info.message(), loc, info.can_unwind());
+            rust_panic_with_hook(
+                &mut StrPanicPayload(msg),
+                info.message(),
+                loc,
+                info.can_unwind(),
+                info.force_no_backtrace(),
+            );
         } else {
             rust_panic_with_hook(
                 &mut PanicPayload::new(msg),
                 info.message(),
                 loc,
                 info.can_unwind(),
+                info.force_no_backtrace(),
             );
         }
     })
@@ -647,7 +658,13 @@ pub const fn begin_panic<M: Any + Send>(msg: M) -> ! {
 
     let loc = Location::caller();
     return crate::sys_common::backtrace::__rust_end_short_backtrace(move || {
-        rust_panic_with_hook(&mut PanicPayload::new(msg), None, loc, true)
+        rust_panic_with_hook(
+            &mut PanicPayload::new(msg),
+            None,
+            loc,
+            /* can_unwind */ true,
+            /* force_no_backtrace */ false,
+        )
     });
 
     struct PanicPayload<A> {
@@ -693,6 +710,7 @@ fn rust_panic_with_hook(
     message: Option<&fmt::Arguments<'_>>,
     location: &Location<'_>,
     can_unwind: bool,
+    force_no_backtrace: bool,
 ) -> ! {
     let must_abort = panic_count::increase(true);
 
@@ -707,14 +725,20 @@ fn rust_panic_with_hook(
             panic_count::MustAbort::AlwaysAbort => {
                 // Unfortunately, this does not print a backtrace, because creating
                 // a `Backtrace` will allocate, which we must to avoid here.
-                let panicinfo = PanicInfo::internal_constructor(message, location, can_unwind);
+                let panicinfo = PanicInfo::internal_constructor(
+                    message,
+                    location,
+                    can_unwind,
+                    force_no_backtrace,
+                );
                 rtprintpanic!("{panicinfo}\npanicked after panic::always_abort(), aborting.\n");
             }
         }
         crate::sys::abort_internal();
     }
 
-    let mut info = PanicInfo::internal_constructor(message, location, can_unwind);
+    let mut info =
+        PanicInfo::internal_constructor(message, location, can_unwind, force_no_backtrace);
     let hook = HOOK.read().unwrap_or_else(PoisonError::into_inner);
     match *hook {
         // Some platforms (like wasm) know that printing to stderr won't ever actually
diff --git a/library/std/src/time.rs b/library/std/src/time.rs
index 00e2857a137..c638cc61856 100644
--- a/library/std/src/time.rs
+++ b/library/std/src/time.rs
@@ -176,6 +176,14 @@ pub struct Instant(time::Instant);
 /// The size of a `SystemTime` struct may vary depending on the target operating
 /// system.
 ///
+/// A `SystemTime` does not count leap seconds.
+/// `SystemTime::now()`'s behaviour around a leap second
+/// is the same as the operating system's wall clock.
+/// The precise behaviour near a leap second
+/// (e.g. whether the clock appears to run slow or fast, or stop, or jump)
+/// depends on platform and configuration,
+/// so should not be relied on.
+///
 /// Example:
 ///
 /// ```no_run
@@ -461,6 +469,9 @@ impl fmt::Debug for Instant {
 impl SystemTime {
     /// An anchor in time which can be used to create new `SystemTime` instances or
     /// learn about where in time a `SystemTime` lies.
+    //
+    // NOTE! this documentation is duplicated, here and in std::time::UNIX_EPOCH.
+    // The two copies are not quite identical, because of the difference in naming.
     ///
     /// This constant is defined to be "1970-01-01 00:00:00 UTC" on all systems with
     /// respect to the system clock. Using `duration_since` on an existing
@@ -468,6 +479,11 @@ impl SystemTime {
     /// measurement lies, and using `UNIX_EPOCH + duration` can be used to create a
     /// `SystemTime` instance to represent another fixed point in time.
     ///
+    /// `duration_since(UNIX_EPOCH).unwrap().as_secs()` returns
+    /// the number of non-leap seconds since the start of 1970 UTC.
+    /// This is a POSIX `time_t` (as a `u64`),
+    /// and is the same time representation as used in many Internet protocols.
+    ///
     /// # Examples
     ///
     /// ```no_run
@@ -617,6 +633,9 @@ impl fmt::Debug for SystemTime {
 
 /// An anchor in time which can be used to create new `SystemTime` instances or
 /// learn about where in time a `SystemTime` lies.
+//
+// NOTE! this documentation is duplicated, here and in SystemTime::UNIX_EPOCH.
+// The two copies are not quite identical, because of the difference in naming.
 ///
 /// This constant is defined to be "1970-01-01 00:00:00 UTC" on all systems with
 /// respect to the system clock. Using `duration_since` on an existing
@@ -624,6 +643,11 @@ impl fmt::Debug for SystemTime {
 /// measurement lies, and using `UNIX_EPOCH + duration` can be used to create a
 /// [`SystemTime`] instance to represent another fixed point in time.
 ///
+/// `duration_since(UNIX_EPOCH).unwrap().as_secs()` returns
+/// the number of non-leap seconds since the start of 1970 UTC.
+/// This is a POSIX `time_t` (as a `u64`),
+/// and is the same time representation as used in many Internet protocols.
+///
 /// # Examples
 ///
 /// ```no_run