Rollup merge of #123879 - beetrees:missing-unsafe, r=Mark-Simulacrum

Add missing `unsafe` to some internal `std` functions

Adds `unsafe` to a few internal functions that have safety requirements but were previously not marked as `unsafe`. Specifically:

- `std::sys::pal::unix::thread::min_stack_size` needs to be `unsafe` as `__pthread_get_minstack` might dereference the passed pointer. All callers currently pass a valid initialised `libc::pthread_attr_t`.
- `std::thread::Thread::new` (and `new_inner`) need to be `unsafe` as it requires the passed thread name to be valid UTF-8, otherwise `Thread::name` will trigger undefined behaviour. I've taken the opportunity to split out the unnamed thread case into a separate `new_unnamed` function to make the safety requirement clearer. All callers meet the safety requirement now that #123505 has been merged.

2 files changed, 4 insertions, 4 deletions

diff --git a/library/std/src/sys/pal/unix/thread.rs b/library/std/src/sys/pal/unix/thread.rs
index 5eb71f1f5ce..6a6bfc77a85 100644
--- a/library/std/src/sys/pal/unix/thread.rs
+++ b/library/std/src/sys/pal/unix/thread.rs
@@ -709,7 +709,7 @@ mod cgroups {
 // is created in an application with big thread-local storage requirements.
 // See #6233 for rationale and details.
 #[cfg(all(target_os = "linux", target_env = "gnu"))]
-fn min_stack_size(attr: *const libc::pthread_attr_t) -> usize {
+unsafe fn min_stack_size(attr: *const libc::pthread_attr_t) -> usize {
     // We use dlsym to avoid an ELF version dependency on GLIBC_PRIVATE. (#23628)
     // We shouldn't really be using such an internal symbol, but there's currently
     // no other way to account for the TLS size.
@@ -723,11 +723,11 @@ fn min_stack_size(attr: *const libc::pthread_attr_t) -> usize {
 
 // No point in looking up __pthread_get_minstack() on non-glibc platforms.
 #[cfg(all(not(all(target_os = "linux", target_env = "gnu")), not(target_os = "netbsd")))]
-fn min_stack_size(_: *const libc::pthread_attr_t) -> usize {
+unsafe fn min_stack_size(_: *const libc::pthread_attr_t) -> usize {
     libc::PTHREAD_STACK_MIN
 }
 
 #[cfg(target_os = "netbsd")]
-fn min_stack_size(_: *const libc::pthread_attr_t) -> usize {
+unsafe fn min_stack_size(_: *const libc::pthread_attr_t) -> usize {
     2048 // just a guess
 }
diff --git a/library/std/src/sys/sync/rwlock/queue.rs b/library/std/src/sys/sync/rwlock/queue.rs
index d1918855797..337cc6c2ca0 100644
--- a/library/std/src/sys/sync/rwlock/queue.rs
+++ b/library/std/src/sys/sync/rwlock/queue.rs
@@ -202,7 +202,7 @@ impl Node {
     fn prepare(&mut self) {
         // Fall back to creating an unnamed `Thread` handle to allow locking in
         // TLS destructors.
-        self.thread.get_or_init(|| thread::try_current().unwrap_or_else(|| Thread::new(None)));
+        self.thread.get_or_init(|| thread::try_current().unwrap_or_else(Thread::new_unnamed));
         self.completed = AtomicBool::new(false);
     }