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/** Struct to hold general purpose register values */

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)

{

    // dprintf("Userspace:  .uspace_uarg(%X), .uspace_entry(%X), .uspace_stack(%X)\n",

    //  (unsigned int)(kernel_uarg->uspace_uarg), kernel_uarg->uspace_entry,

    //  kernel_uarg->uspace_stack);

    volatile ustate_t ustate;

    // set first parameter

    ustate.r0 = (uintptr_t) kernel_uarg->uspace_uarg;

    // clear other registers

    ustate.r1 = ustate.r2  = ustate.r3  = ustate.r4  =

        ustate.r5 = ustate.r6  = ustate.r7  = ustate.r8  =

        ustate.r9 = ustate.r10 = ustate.r11 = ustate.r12 = 1;

    ustate.lr = 3;

    //set user stack

    ustate.sp = ((uint32_t)kernel_uarg->uspace_stack) +

            PAGE_SIZE - sizeof(void*);

    //on the bottom of stack there is pointer to TLS

    //set where uspace execution starts

    ustate.pc = (uintptr_t) kernel_uarg->uspace_entry;

    //status register in user mode

    ipl_t cpsr = current_status_reg_read();

    cpsr &= ~STATUS_REG_MODE_MASK | USER_MODE;

    ipl_t tmpsr = (cpsr & ~STATUS_REG_MODE_MASK) | SUPERVISOR_MODE;

    asm __volatile__ (

        // save pointer into ustate struct

        "mov r0, %0         \n"

        // save cspr

        "mov r1, %1         \n"

        // change mode into any exception mode

        "msr cpsr_c, %2         \n"

        // set saved cpsr

        "msr spsr_c, r1 \n"

        "mov sp, r0 \n"

        // replace almost all registers

        "ldmfd sp!, {r0-r12, sp, lr}^\n"

        //jump to the usermode

        "ldmfd sp!, {pc}^"

    : // no output

    : "r"(&ustate), "r"(cpsr), "r"(tmpsr) //

    : "r0","r1"

    );

    while(1) ;

}