Index: lib/libthr/thread/thr_init.c
===================================================================
--- lib/libthr/thread/thr_init.c
+++ lib/libthr/thread/thr_init.c
@@ -61,7 +61,7 @@
 #include "libc_private.h"
 #include "thr_private.h"
 
-char		*_usrstack;
+char		*_stacktop;
 struct pthread	*_thr_initial;
 int		_libthr_debug;
 int		_thread_event_mask;
@@ -388,7 +388,7 @@
 	 * resource limits, so this stack needs an explicitly mapped
 	 * red zone to protect the thread stack that is just beyond.
 	 */
-	if (mmap(_usrstack - _thr_stack_initial -
+	if (mmap(_stacktop - _thr_stack_initial -
 	    _thr_guard_default, _thr_guard_default, 0, MAP_ANON,
 	    -1, 0) == MAP_FAILED)
 		PANIC("Cannot allocate red zone for initial thread");
@@ -402,7 +402,7 @@
 	 *       actually free() it; it just puts it in the free
 	 *       stack queue for later reuse.
 	 */
-	thread->attr.stackaddr_attr = _usrstack - _thr_stack_initial;
+	thread->attr.stackaddr_attr = _stacktop - _thr_stack_initial;
 	thread->attr.stacksize_attr = _thr_stack_initial;
 	thread->attr.guardsize_attr = _thr_guard_default;
 	thread->attr.flags |= THR_STACK_USER;
@@ -427,7 +427,7 @@
 	thread->attr.prio = sched_param.sched_priority;
 
 #ifdef _PTHREAD_FORCED_UNWIND
-	thread->unwind_stackend = _usrstack;
+	thread->unwind_stackend = _stacktop;
 #endif
 
 	/* Others cleared to zero by thr_alloc() */
@@ -464,10 +464,13 @@
 		__thr_malloc_init();
 		/* Find the stack top */
 		mib[0] = CTL_KERN;
-		mib[1] = KERN_USRSTACK;
-		len = sizeof (_usrstack);
-		if (sysctl(mib, 2, &_usrstack, &len, NULL, 0) == -1)
-			PANIC("Cannot get kern.usrstack from sysctl");
+		mib[1] = KERN_STACKTOP;
+		len = sizeof (_stacktop);
+		if (sysctl(mib, 2, &_stacktop, &len, NULL, 0) == -1) {
+			mib[1] = KERN_USRSTACK;
+			if (sysctl(mib, 2, &_stacktop, &len, NULL, 0) == -1)
+				PANIC("Cannot get kern.usrstack from sysctl");
+		}
 		env_bigstack = getenv("LIBPTHREAD_BIGSTACK_MAIN");
 		env_splitstack = getenv("LIBPTHREAD_SPLITSTACK_MAIN");
 		if (env_bigstack != NULL || env_splitstack == NULL) {
Index: lib/libthr/thread/thr_private.h
===================================================================
--- lib/libthr/thread/thr_private.h
+++ lib/libthr/thread/thr_private.h
@@ -724,7 +724,7 @@
  * Global variables for the pthread kernel.
  */
 
-extern char		*_usrstack __hidden;
+extern char		*_stacktop __hidden;
 
 /* For debugger */
 extern int		_libthr_debug;
Index: lib/libthr/thread/thr_stack.c
===================================================================
--- lib/libthr/thread/thr_stack.c
+++ lib/libthr/thread/thr_stack.c
@@ -149,18 +149,20 @@
 {
 	int mib[2];
 	struct rlimit rlim;
-	u_long usrstack;
+	u_long stacktop;
 	size_t len;
 
 	mib[0] = CTL_KERN;
-	mib[1] = KERN_USRSTACK;
-	len = sizeof(usrstack);
-	if (sysctl(mib, sizeof(mib) / sizeof(mib[0]), &usrstack, &len, NULL, 0)
-	    == -1)
-		return;
+	mib[1] = KERN_STACKTOP;
+	len = sizeof(stacktop);
+	if (sysctl(mib, nitems(mib), &stacktop, &len, NULL, 0) == -1) {
+		mib[1] = KERN_USRSTACK;
+		if (sysctl(mib, nitems(mib), &stacktop, &len, NULL, 0) == -1)
+			return;
+	}
 	if (getrlimit(RLIMIT_STACK, &rlim) == -1)
 		return;
-	mprotect((void *)(uintptr_t)(usrstack - rlim.rlim_cur),
+	mprotect((void *)(uintptr_t)(stacktop - rlim.rlim_cur),
 	    rlim.rlim_cur, _rtld_get_stack_prot());
 }
 
@@ -213,7 +215,7 @@
 
 	/*
 	 * Use the garbage collector lock for synchronization of the
-	 * spare stack lists and allocations from usrstack.
+	 * spare stack lists and allocations from stacktop.
 	 */
 	THREAD_LIST_WRLOCK(curthread);
 	/*
@@ -249,11 +251,11 @@
 	}
 	else {
 		/*
-		 * Allocate a stack from or below usrstack, depending
+		 * Allocate a stack from or below stacktop, depending
 		 * on the LIBPTHREAD_BIGSTACK_MAIN env variable.
 		 */
 		if (last_stack == NULL)
-			last_stack = _usrstack - _thr_stack_initial -
+			last_stack = _stacktop - _thr_stack_initial -
 			    _thr_guard_default;
 
 		/* Allocate a new stack. */