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/*
 * Copyright (c) 2007 Petr Stepan, Pavel Jancik
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - 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.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 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.
 */

/** @addtogroup arm32
 * @{
 */
/** @file
 *  @brief Userspace switch.
 */

#include <userspace.h>

/** Struct for holding all general purpose registers.
 *  
 *  Used to set registers when going to userspace.
 */
typedef struct {
    uint32_t r0;
    uint32_t r1;
    uint32_t r2;
    uint32_t r3;
    uint32_t r4;
    uint32_t r5;
    uint32_t r6;
    uint32_t r7;
    uint32_t r8;
    uint32_t r9;
    uint32_t r10;
    uint32_t r11;
    uint32_t r12;
    uint32_t sp;
    uint32_t lr;
    uint32_t pc;
} ustate_t;

/** Changes processor mode and jumps to the address specified in the first
 * parameter.
 *
 *  @param kernel_uarg   Userspace settings (entry point, stack, ...).
 */
void userspace(uspace_arg_t *kernel_uarg)
{
    volatile ustate_t ustate;

    /* set first parameter */
    ustate.r0 = (uintptr_t) kernel_uarg->uspace_uarg;

    /* %r1 is defined to hold pcb_ptr - set it to 0 */
    ustate.r1 = 0;

    /* clear other registers */
    ustate.r2 = ustate.r3  = ustate.r4  = ustate.r5 =
        ustate.r6  = ustate.r7  = ustate.r8  = ustate.r9 = ustate.r10 = 
        ustate.r11 = ustate.r12 = ustate.lr = 0;

    /* set user stack */
    ustate.sp = ((uint32_t)kernel_uarg->uspace_stack) + PAGE_SIZE;

    /* set where uspace execution starts */
    ustate.pc = (uintptr_t) kernel_uarg->uspace_entry;

    /* status register in user mode */
    ipl_t user_mode = current_status_reg_read() &
        (~STATUS_REG_MODE_MASK | USER_MODE);

    /* set user mode, set registers, jump */
    asm volatile (
        "mov sp, %[ustate]\n"
        "msr spsr_c, %[user_mode]\n"
        "ldmfd sp!, {r0-r12, sp, lr}^\n"
        "ldmfd sp!, {pc}^\n"
        :: [ustate] "r" (&ustate), [user_mode] "r" (user_mode)
    );

    /* unreachable */
    while(1)
        ;
}

/** @}
 */