std: make stack guard page location available during TLS destruction

Author: joboet

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

@@ -42,7 +42,7 @@ mod imp {
     use crate::io;
     use crate::mem;
     use crate::ptr;
-    use crate::thread;
+    use crate::sys_common::thread_info::current_thread;
 
     use libc::MAP_FAILED;
     #[cfg(not(all(target_os = "linux", target_env = "gnu")))]
@@ -89,10 +89,9 @@ mod imp {
         // If the faulting address is within the guard page, then we print a
         // message saying so and abort.
         if guard.start <= addr && addr < guard.end {
-            rtprintpanic!(
-                "\nthread '{}' has overflowed its stack\n",
-                thread::current().name().unwrap_or("<unknown>")
-            );
+            let thread = current_thread();
+            let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unknown>");
+            rtprintpanic!("\nthread '{}' has overflowed its stack\n", name);
             rtabort!("stack overflow");
         } else {
             // Unregister ourselves by reverting back to the default behavior.

library/std/src/sys_common/thread_info.rs

@@ -1,47 +1,41 @@
 #![allow(dead_code)] // stack_guard isn't used right now on all platforms
-#![allow(unused_unsafe)] // thread_local with `const {}` triggers this liny
 
-use crate::cell::RefCell;
+use crate::cell::Cell;
 use crate::sys::thread::guard::Guard;
 use crate::thread::Thread;
 
-struct ThreadInfo {
-    stack_guard: Option<Guard>,
-    thread: Thread,
-}
-
-thread_local! { static THREAD_INFO: RefCell<Option<ThreadInfo>> = const { RefCell::new(None) } }
-
-impl ThreadInfo {
-    fn with<R, F>(f: F) -> Option<R>
-    where
-        F: FnOnce(&mut ThreadInfo) -> R,
-    {
-        THREAD_INFO
-            .try_with(move |thread_info| {
-                let mut thread_info = thread_info.borrow_mut();
-                let thread_info = thread_info.get_or_insert_with(|| ThreadInfo {
-                    stack_guard: None,
-                    thread: Thread::new(None),
-                });
-                f(thread_info)
-            })
-            .ok()
-    }
+thread_local! {
+    static THREAD: Cell<Option<Thread>> = const { Cell::new(None) };
+    // Use a separate thread local for the stack guard page location.
+    // Since `Guard` does not implement drop, this is always available
+    // on systems with ELF-TLS, in particular during TLS destruction.
+    static STACK_GUARD: Cell<Option<Guard>> = const { Cell::new(None) };
 }
 
 pub fn current_thread() -> Option<Thread> {
-    ThreadInfo::with(|info| info.thread.clone())
+    THREAD
+        .try_with(|thread| {
+            let t = thread.take().unwrap_or_else(|| Thread::new(None));
+            let t2 = t.clone();
+            thread.set(Some(t));
+            t2
+        })
+        .ok()
 }
 
 pub fn stack_guard() -> Option<Guard> {
-    ThreadInfo::with(|info| info.stack_guard.clone()).and_then(|o| o)
+    STACK_GUARD
+        .try_with(|guard| {
+            let g = guard.take();
+            let g2 = g.clone();
+            guard.set(g);
+            g2
+        })
+        .ok()
+        .flatten()
 }
 
 pub fn set(stack_guard: Option<Guard>, thread: Thread) {
-    THREAD_INFO.with(move |thread_info| {
-        let mut thread_info = thread_info.borrow_mut();
-        rtassert!(thread_info.is_none());
-        *thread_info = Some(ThreadInfo { stack_guard, thread });
-    });
+    rtassert!(STACK_GUARD.replace(stack_guard).is_none());
+    rtassert!(THREAD.replace(Some(thread)).is_none());
 }

tests/ui/abi/stack-probes.rs

@@ -44,7 +44,10 @@ fn main() {
     // details
     if cfg!(not(target_os = "linux")) {
         assert_overflow(Command::new(&me).arg("main-recurse"));
-        assert_overflow(Command::new(&me).arg("main-tls-recurse"));
+        // FIXME: This does not seem to work on macOS.
+        if cfg!(not(target_os = "macos")) {
+            assert_overflow(Command::new(&me).arg("main-tls-recurse"));
+        }
     }
     assert_overflow(Command::new(&me).arg("child-recurse"));
     assert_overflow(Command::new(&me).arg("child-tls-recurse"));