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  1. /*
  2.  * Copyright (c) 2007 Petr Stepan, Pavel Jancik
  3.  * All rights reserved.
  4.  *
  5.  * Redistribution and use in source and binary forms, with or without
  6.  * modification, are permitted provided that the following conditions
  7.  * are met:
  8.  *
  9.  * - Redistributions of source code must retain the above copyright
  10.  *   notice, this list of conditions and the following disclaimer.
  11.  * - Redistributions in binary form must reproduce the above copyright
  12.  *   notice, this list of conditions and the following disclaimer in the
  13.  *   documentation and/or other materials provided with the distribution.
  14.  * - The name of the author may not be used to endorse or promote products
  15.  *   derived from this software without specific prior written permission.
  16.  *
  17.  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  18.  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  19.  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  20.  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  21.  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  22.  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23.  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24.  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25.  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  26.  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27.  */
  28.  
  29. /** @addtogroup arm32
  30.  * @{
  31.  */
  32. /** @file
  33.  */
  34.  
  35. #include <userspace.h>
  36.  
  37. /** Struct to hold general purpose register values */
  38. typedef struct {
  39.     uint32_t r0;
  40.     uint32_t r1;
  41.     uint32_t r2;
  42.     uint32_t r3;
  43.     uint32_t r4;
  44.     uint32_t r5;
  45.     uint32_t r6;
  46.     uint32_t r7;
  47.     uint32_t r8;
  48.     uint32_t r9;
  49.     uint32_t r10;
  50.     uint32_t r11;
  51.     uint32_t r12;
  52.     uint32_t sp;
  53.     uint32_t lr;
  54.     uint32_t pc;
  55. } ustate_t;
  56.  
  57. /** Changes processor mode and jumps to the address specified in the first parameter.
  58.  *
  59.  *  @param kernel_uarg   Userspace settings (entry point, stack, ...).
  60.  */
  61. void userspace(uspace_arg_t *kernel_uarg)
  62. {
  63.  
  64.     volatile ustate_t ustate;
  65.  
  66.     // set first parameter
  67.     ustate.r0 = (uintptr_t) kernel_uarg->uspace_uarg;
  68.  
  69.     // clear other registers
  70.     ustate.r1 = ustate.r2  = ustate.r3  = ustate.r4  =
  71.         ustate.r5 = ustate.r6  = ustate.r7  = ustate.r8  =
  72.         ustate.r9 = ustate.r10 = ustate.r11 = ustate.r12 =
  73.         ustate.lr = 0;
  74.  
  75.     //set user stack
  76.     ustate.sp = ((uint32_t)kernel_uarg->uspace_stack) +
  77.             PAGE_SIZE - sizeof(void*);
  78.  
  79.     //set where uspace execution starts
  80.     ustate.pc = (uintptr_t) kernel_uarg->uspace_entry;
  81.  
  82.     //status register in user mode
  83.     ipl_t cpsr = current_status_reg_read();
  84.     cpsr &= ~STATUS_REG_MODE_MASK | USER_MODE;
  85.  
  86.     ipl_t tmpsr = (cpsr & ~STATUS_REG_MODE_MASK) | SUPERVISOR_MODE;
  87.  
  88.     asm __volatile__ (
  89.         // save pointer into ustate struct
  90.         "mov r0, %0         \n"
  91.         // save cspr
  92.         "mov r1, %1         \n"
  93.         // change mode into any exception mode
  94.         "msr cpsr_c, %2         \n"
  95.         // set saved cpsr
  96.         "msr spsr_c, r1 \n"
  97.  
  98.         "mov sp, r0 \n"
  99.         // replace almost all registers
  100.         "ldmfd sp!, {r0-r12, sp, lr}^\n"
  101.         //jump to the usermode
  102.         "ldmfd sp!, {pc}^"
  103.     : // no output
  104.     : "r"(&ustate), "r"(cpsr), "r"(tmpsr) //
  105.     : "r0","r1"
  106.     );
  107.  
  108.     // unreachable
  109.     while(1) ;
  110. }
  111.  
  112.  
  113. /** @}
  114.  */
  115.