kernel/usermode.c


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#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: \
    "); 
}