changed kernel stack top to 0x40000000 (1GB) virtual

git-svn-id: svn://anubis/hos/trunk@81 5b3e749e-e535-0410-8002-a9bb6afbdfca

kernel/sys/cpu.h

@@ -34,4 +34,7 @@ static u32_t read_cr3()
 #define write_cr3(val) \
     __asm__ __volatile__ ("movl %0, %%cr3" : : "r" (val));
 
+#define write_esp(val) \
+    __asm__ __volatile__ ("movl %0, %%esp" : : "r" (val));
+
 #endif