runtime: fix timediv calls on NetBSD, OpenBSD

Document endian-ness assumption.

R=dvyukov
CC=golang-dev
https://golang.org/cl/12056044

src/pkg/runtime/os_freebsd.c

@@ -54,6 +54,7 @@ runtime·futexsleep(uint32 *addr, uint32 val, int64 ns)
 			return;
 		goto fail;
 	}
+	// NOTE: tv_nsec is int64 on amd64, so this assumes a little-endian system.
 	ts.tv_nsec = 0;
 	ts.tv_sec = runtime·timediv(ns, 1000000000, (int32*)&ts.tv_nsec);
 	ret = runtime·sys_umtx_op(addr, UMTX_OP_WAIT_UINT, val, nil, &ts);

src/pkg/runtime/os_linux.c

@@ -48,6 +48,7 @@ runtime·futexsleep(uint32 *addr, uint32 val, int64 ns)
 		runtime·futex(addr, FUTEX_WAIT, val, nil, nil, 0);
 		return;
 	}
+	// NOTE: tv_nsec is int64 on amd64, so this assumes a little-endian system.
 	ts.tv_nsec = 0;
 	ts.tv_sec = runtime·timediv(ns, 1000000000LL, (int32*)&ts.tv_nsec);
 	runtime·futex(addr, FUTEX_WAIT, val, &ts, nil, 0);

src/pkg/runtime/os_netbsd.c

@@ -95,8 +95,9 @@ runtime·semasleep(int64 ns)
 				runtime·lwp_park(nil, 0, &m->waitsemacount, nil);
 			} else {
 				ns += runtime·nanotime();
+				// NOTE: tv_nsec is int64 on amd64, so this assumes a little-endian system.
 				ts.tv_nsec = 0;
-				ts.tv_sec = runtime·timediv(ns, 1000000000, (int32*)ts.tv_nsec);
+				ts.tv_sec = runtime·timediv(ns, 1000000000, (int32*)&ts.tv_nsec);
 				// TODO(jsing) - potential deadlock!
 				// See above for details.
 				runtime·atomicstore(&m->waitsemalock, 0);

src/pkg/runtime/os_openbsd.c

@@ -78,8 +78,9 @@ runtime·semasleep(int64 ns)
 				runtime·thrsleep(&m->waitsemacount, 0, nil, &m->waitsemalock, nil);
 			else {
 				ns += runtime·nanotime();
+				// NOTE: tv_nsec is int64 on amd64, so this assumes a little-endian system.
 				ts.tv_nsec = 0;
-				ts.tv_sec = runtime·timediv(ns, 1000000000, (int32*)ts.tv_nsec);
+				ts.tv_sec = runtime·timediv(ns, 1000000000, (int32*)&ts.tv_nsec);
 				runtime·thrsleep(&m->waitsemacount, CLOCK_REALTIME, &ts, &m->waitsemalock, nil);
 			}
 			// reacquire lock