Auto merge of #160114 - windsornguyen:fix/musl-lto-weak-gettid, r=<try>

Avoid weak-linking `gettid` on musl


try-job: test-various

Author: bors

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

@@ -335,6 +335,13 @@ pub fn current_os_id() -> Option<u64> {
     // The OS thread ID is used rather than `pthread_self` so as to match what will be displayed
     // for process inspection (debuggers, trace, `top`, etc.).
     cfg_select! {
+        all(target_os = "linux", target_env = "musl") => {
+            // Under fat LTO, weak-linking `gettid` can turn strong declarations weak.
+            // musl provides `gettid`, so call it directly. See #154439.
+            // SAFETY: FFI call with no preconditions.
+            let id: libc::pid_t = unsafe { libc::gettid() };
+            Some(id as u64)
+        }
         // Most platforms have a function returning a `pid_t` or int, which is an `i32`.
         any(target_os = "android", target_os = "linux") => {
             use crate::sys::pal::weak::syscall;

tests/ui/linking/auxiliary/strong-gettid-ref.rs

@@ -0,0 +1,14 @@
+// This crate must sort after `std` to reproduce #154439.
+
+//@ no-prefer-dynamic
+//@ compile-flags: -Copt-level=3
+
+#![crate_type = "rlib"]
+
+unsafe extern "C" {
+    safe fn gettid() -> i32;
+}
+
+pub fn tid() -> i32 {
+    gettid()
+}

tests/ui/linking/lto-weak-gettid-issue-154439.rs

@@ -0,0 +1,14 @@
+//! Regression test for std weakening a strong `gettid` reference under fat LTO (#154439).
+
+//@ run-pass
+//@ only-linux
+//@ aux-build: strong-gettid-ref.rs
+//@ no-prefer-dynamic
+//@ compile-flags: -Copt-level=3 -Clto=fat -Ctarget-feature=+crt-static
+
+extern crate strong_gettid_ref;
+
+fn main() {
+    // The main thread's TID equals its PID.
+    assert_eq!(strong_gettid_ref::tid() as u32, std::process::id());
+}