started implementing usermode switch

1 files changed, 32 insertions, 0 deletions

diff --git a/kernel/usermode.c b/kernel/usermode.c
new file mode 100644
index 0000000..afad9df
--- /dev/null
+++ b/kernel/usermode.c
@@ -0,0 +1,32 @@
+#include "usermode.h"
+
+
+void install_tss(int cpu_no){
+    // now fill each value
+    // set values necessary
+    sys_tss.ss0 = 0x10;
+              // now set the IO bitmap (not necessary, so set above limit)       
+    sys_tss.iomap = ( unsigned short ) sizeof( tss_struct ); 
+}
+
+void switch_to_user_mode() {
+    // Set up a stack structure for switching to user mode.
+    asm volatile("  \
+        cli; \
+        mov $0x23, %ax; \
+        mov %ax, %ds; \
+        mov %ax, %es; \
+        mov %ax, %fs; \
+        mov %ax, %gs; \
+                \ 
+        mov %esp, %eax; \
+        pushl $0x23; \
+        pushl %eax; \
+        pushf; \
+        mov $0x200, %eax; \
+        push %eax; \
+        pushl $0x1B; \
+        push $1f; \
+        iret; \    1: \
+    "); 
+}