/* ctxsw.S - ctxsw (for x86) */

                .text
                .globl  ctxsw

/*------------------------------------------------------------------------
 * ctxsw -  X86 context switch; the call is ctxsw(&old_sp, &new_sp)
 *------------------------------------------------------------------------
 */
ctxsw:
                pushl   %ebp            /* Push ebp onto stack          */
                movl    %esp,%ebp       /* Record current SP in ebp     */
                pushfl                  /* Push flags onto the stack    */
                pushal                  /* Push general regs. on stack  */

                /* Save old segment registers here, if multiple allowed */

                movl    8(%ebp),%eax    /* Get mem location in which to */
                                        /*   save the old process's SP  */
                movl    %esp,(%eax)     /* Save old process's SP        */
                movl    12(%ebp),%eax   /* Get location from which to   */
                                        /*   restore new process's SP   */

                /* The next instruction switches from the old process's */
                /*   stack to the new process's stack.                  */

                movl    (%eax),%esp     /* Pick up new process's SP     */

                /* Restore new seg. registers here, if multiple allowed */

                popal                   /* Restore general registers    */
                movl    4(%esp),%ebp    /* Pick up ebp before restoring */
                                        /*   interrupts                 */
                popfl                   /* Restore interrupt mask       */
                add     $4,%esp         /* Skip saved value of ebp      */
                ret                     /* Return to new process        */