sim: Fix sim stack smashing problem

The reason is that the new created task receives signal while
it has not entered its stack frame.

Signed-off-by: chenxiaoyi <chenxiaoyi@xiaomi.com>

arch/sim/src/sim/sim_initialstate.c

@@ -32,8 +32,26 @@
 
 #include <nuttx/arch.h>
 
+#include "sched/sched.h"
 #include "sim_internal.h"
 
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+static void pre_start(void)
+{
+  struct tcb_s *tcb = this_task();
+
+  /* Enable signal delivery */
+
+  up_irq_restore(0);
+
+  /* Then call the real start function */
+
+  tcb->start();
+}
+
 /****************************************************************************
  * Public Functions
  ****************************************************************************/
@@ -93,7 +111,11 @@ void up_initial_state(struct tcb_s *tcb)
 #endif
                                    + tcb->adj_stack_size;
 
-  tcb->xcp.regs[JB_PC] = (xcpt_reg_t)tcb->start;
+  /* Mask the interrupt until switching to the new task */
+
+  memset(&tcb->xcp.regs[JB_FLAG], 0xff, sizeof(xcpt_reg_t) * 2);
+
+  tcb->xcp.regs[JB_PC] = (xcpt_reg_t)pre_start;
 
 #ifdef CONFIG_SIM_ASAN
   __asan_unpoison_memory_region(tcb->stack_alloc_ptr, tcb->adj_stack_size);