further changes from feedback

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

@@ -806,6 +806,8 @@ pub mod guard {
     #[cfg(target_os = "netbsd")]
     unsafe fn get_stack_start() -> Option<*mut libc::c_void> {
         let mut ret = None;
+        // We do not need pthread_attr_init/pthread_attr_destroy
+        // instead we use `pthread_getattr_np` to initialise the thread's attribute
         let mut attr: libc::pthread_attr_t = crate::mem::zeroed();
         let e = libc::pthread_getattr_np(libc::pthread_self(), &mut attr);
         if e == 0 {
@@ -816,7 +818,9 @@ pub mod guard {
             // on netbsd, we need to take in account the guard size to push up
             // the stack's address from the bottom.
             assert_eq!(libc::pthread_attr_getguardsize(&attr, &mut guardsize), 0);
-            stackaddr = stackaddr.add(guardsize);
+            // Only hppa arch seems to support stack growing up to higher address
+            // (__MACHINE_STACK_GROWS_UP)
+            stackaddr = stackaddr.sub(guardsize);
             ret = Some(stackaddr);
         }
         ret