va_arg fix

src/libthread/id.c

diff --git a/src/libthread/id.c b/src/libthread/id.c
index e920b87..d32a92f 100644
--- a/src/libthread/id.c
+++ b/src/libthread/id.c
@@ -64,7 +64,7 @@
 		free(t->cmdname);
 	va_start(arg, fmt);
 	t->cmdname = vsmprint(fmt, arg);
-	va_end(fmt);
+	va_end(arg);
 
 /* Plan 9 only 
 	if(p->nthreads == 1){