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/*-

 * Copyright (c) 2005-2009, Kohsuke Ohtani

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 * 1. Redistributions of source code must retain the above copyright

 *    notice, this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 * 3. Neither the name of the author nor the names of any co-contributors

 *    may be used to endorse or promote products derived from this software

 *    without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND

 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE

 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS

 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY

 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF

 * SUCH DAMAGE.

 */

/*

 * context.c - context management routines

 */

/*

 * The context consists of kernel/user mode registers, and kernel

 * stack. The user mode registers are always saved to the kernel

 * stack when processor enters kernel mode by H/W or S/W events.

 *

 * The user mode registers are located in the interrupt/trap

 * frame at the top of the kernel stack. Before the control

 * returns to user mode next time, these register value will be

 * restored automatically.

 *

 * All thread owns its context to keep its execution state. The

 * scheduler will switch the context to change an active thread.

 */

#include <kernel.h>

#include <kmem.h>

#include <cpu.h>

#include <trap.h>

#include <context.h>

#include <locore.h>

/*

 * Set user mode registers into the specific context.

 *

 * Note: When user mode program counter is set, all register

 * values except a stack pointer are reset to default value.

 */

void

context_set(context_t ctx, int type, register_t val)

{

        struct kern_regs *k;

        struct cpu_regs *u;

        uint32_t *argp;

        k = &ctx->kregs;

        switch (type) {

        case CTX_KSTACK:

                /* Set kernel mode stack pointer */

                ctx->uregs = (struct cpu_regs *)

                                ((uint32_t)val - sizeof(struct cpu_regs));

                ctx->esp0 = (uint32_t)val;

                k->eip = (uint32_t)&syscall_ret;

                k->esp = (uint32_t)ctx->uregs - sizeof(uint32_t);

                /* Reset minimum user mode registers */

                u = ctx->uregs;

                u->eax = 0;

                u->eflags = (uint32_t)(EFL_IF | EFL_IOPL_KERN);

                break;

        case CTX_KENTRY:

                /* Kernel mode program counter */

                k->eip = (uint32_t)val;

                break;

        case CTX_KARG:

                /* Kernel mode argument */

                argp = (uint32_t *)(k->esp + sizeof(uint32_t) * 2);

                *argp = (uint32_t)val;

                break;

        case CTX_USTACK:

                /* User mode stack pointer */

                u = ctx->uregs;

                u->esp = (uint32_t)val;

                u->ss = (uint32_t)(USER_DS | 3); /* fail safe */

                break;

        case CTX_UENTRY:

                /* User mode program counter */

                u = ctx->uregs;

                u->eip = (uint32_t)val;

                u->cs = (uint32_t)(USER_CS | 3);

                u->ds = u->es = (uint32_t)(USER_DS | 3);

                u->eflags = (uint32_t)(EFL_IF | EFL_IOPL_KERN);

                u->eax = u->ebx = u->ecx = u->edx =

                        u->edi = u->esi = u->ebp = 0;

                break;

        case CTX_UARG:

                /* User mode argument */

                u = ctx->uregs;

                argp = (uint32_t *)(u->esp + sizeof(uint32_t));

                copyout(&val, argp, sizeof(uint32_t));

                break;

        default:

                /* invalid */

                break;

        }

}

/*

 * Switch to new context

 *

 * Kernel mode registers and kernel stack pointer are switched to

 * the next context.

 *

 * We don't use x86 task switch mechanism to minimize the context

 * space. The system has only one TSS(task state segment), and

 * the context switching is done by changing the register value

 * in this TSS. Processor will reload them automatically when it

 * enters to the kernel mode in next time.

 *

 * It is assumed all interrupts are disabled by caller.

 *

 * TODO: FPU context is not switched as of now.

 */

void

context_switch(context_t prev, context_t next)

{

        /* Set kernel stack pointer in TSS (esp0). */

        tss_set((uint32_t)next->esp0);

        /* Save the previous context, and restore the next context */

        cpu_switch(&prev->kregs, &next->kregs);

}

/*

 * Save user mode context to handle exceptions.

 *

 * Copy current user mode registers in the kernel stack to the

 * user mode stack. The user stack pointer is adjusted for this

 * area. So that the exception handler can get the register

 * state of the target thread.

 *

 * It builds arguments for the exception handler in the following

 * format.

 *

 *   void exception_handler(int exc, void *regs);

 */

void

context_save(context_t ctx)

{

        struct cpu_regs *cur, *sav;

        /* Copy current register context into user mode stack */

        cur = ctx->uregs;

        sav = (struct cpu_regs *)(cur->esp - sizeof(*sav));

        copyout(cur, sav, sizeof(*sav));

        ctx->saved_regs = sav;

        /* Adjust stack pointer */

        cur->esp = (uint32_t)sav - (sizeof(uint32_t) * 2);

}

/*

 * Restore register context to return from the exception handler.

 */

void

context_restore(context_t ctx)

{

        struct cpu_regs *cur;

        /* Restore user mode context */

        cur = ctx->uregs;

        copyin(ctx->saved_regs, cur, sizeof(*cur));

        /* Correct some registers for fail safe */

        cur->cs = (uint32_t)(USER_CS | 3);

        cur->ss = cur->ds = cur->es = (uint32_t)(USER_DS | 3);

        cur->eflags |= EFL_IF;

}

void

context_dump(context_t ctx)

{

#ifdef DEBUG

        trap_dump(ctx->uregs);

#endif

}