diff --git a/stand/kboot/libkboot/crt1.c b/stand/kboot/libkboot/crt1.c
--- a/stand/kboot/libkboot/crt1.c
+++ b/stand/kboot/libkboot/crt1.c
@@ -57,6 +57,8 @@
 
 #include "start_arch.h"
 
+void *stack_upper_limit;
+
 void
 _start_c(long *p)
 {
@@ -64,6 +66,7 @@
 	const char **argv;
 	char **envp;
 
+	stack_upper_limit = p;		/* Save the upper limit of call stack */
 	argc = p[0];
 	argv = (const char **)(p + 1);
 	envp = (char **)argv + argc + 1;