diff --git a/gc.c b/gc.c
index c345f2113f..c564fa7274 100644
--- a/gc.c
+++ b/gc.c
@@ -4052,6 +4052,8 @@ stack_check(rb_execution_context_t *ec, int water_mark)
 	    ec->machine.register_stack_maxsize/sizeof(VALUE) - water_mark;
     }
 #endif
+    if (ret)
+        fprintf(stderr, "DEBUG: STACK_LENGTH=%zu, STACK_LEVEL_MAX=%zu, water_mark=%d\n", STACK_LENGTH, STACK_LEVEL_MAX, water_mark);
     return ret;
 }
 #else
diff --git a/thread_pthread.c b/thread_pthread.c
index 951885ffa0..68cf3e3bce 100644
--- a/thread_pthread.c
+++ b/thread_pthread.c
@@ -544,11 +544,13 @@ get_stack(void **addr, size_t *size)
 #define CHECK_ERR(expr)				\
     {int err = (expr); if (err) return err;}
 #ifdef HAVE_PTHREAD_GETATTR_NP /* Linux */
+// musl
     pthread_attr_t attr;
     size_t guard = 0;
     STACK_GROW_DIR_DETECTION;
     CHECK_ERR(pthread_getattr_np(pthread_self(), &attr));
 # ifdef HAVE_PTHREAD_ATTR_GETSTACK
+// musl
     CHECK_ERR(pthread_attr_getstack(&attr, addr, size));
     STACK_DIR_UPPER((void)0, (void)(*addr = (char *)*addr + *size));
 # else
@@ -556,6 +558,7 @@ get_stack(void **addr, size_t *size)
     CHECK_ERR(pthread_attr_getstacksize(&attr, size));
 # endif
 # ifdef HAVE_PTHREAD_ATTR_GETGUARDSIZE
+// musl
     CHECK_ERR(pthread_attr_getguardsize(&attr, &guard));
     *size -= guard;
 # else
@@ -722,6 +725,7 @@ ruby_init_stack(volatile VALUE *addr
     }
 #endif
 #if MAINSTACKADDR_AVAILABLE
+// musl
     if (native_main_thread.stack_maxsize) return;
     {
 	void* stackaddr;
@@ -730,6 +734,7 @@ ruby_init_stack(volatile VALUE *addr
 	    native_main_thread.stack_maxsize = size;
 	    native_main_thread.stack_start = stackaddr;
 	    reserve_stack(stackaddr, size);
+	    fprintf(stderr, "DEBUG: stack_maxsize=%zu\n", size);
 	    goto bound_check;
 	}
     }
@@ -737,6 +742,7 @@ ruby_init_stack(volatile VALUE *addr
 #ifdef STACK_END_ADDRESS
     native_main_thread.stack_start = STACK_END_ADDRESS;
 #else
+//  musl
     if (!native_main_thread.stack_start ||
         STACK_UPPER((VALUE *)(void *)&addr,
                     native_main_thread.stack_start > addr,