ArmPlatformPkg/Sec/Helper.S

   1 #========================================================================================
   2 #  Copyright (c) 2011, ARM Limited. All rights reserved.
   3 #
   4 #  This program and the accompanying materials
   5 #  are licensed and made available under the terms and conditions of the BSD License
   6 #  which accompanies this distribution.  The full text of the license may be found at
   7 #  http:#opensource.org/licenses/bsd-license.php
   8 #
   9 #  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  10 #  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  11 #
  12 #=======================================================================================
  13
  14 #start of the code section
  15 .text
  16 .align 3
  17
  18 GCC_ASM_EXPORT(monitor_vector_table)
  19 GCC_ASM_EXPORT(return_from_exception)
  20 GCC_ASM_EXPORT(enter_monitor_mode)
  21 GCC_ASM_EXPORT(copy_cpsr_into_spsr)
  22
  23 ASM_PFX(monitor_vector_table):
  24     ldr pc, dead
  25     ldr pc, dead
  26     ldr pc, dead
  27     ldr pc, dead
  28     ldr pc, dead
  29     ldr pc, dead
  30     ldr pc, dead
  31     ldr pc, dead
  32
  33 # arg0: Secure Monitor mode stack
  34 ASM_PFX(enter_monitor_mode):
  35     mov     r2, lr                      @ Save current lr
  36
  37     mrs     r1, cpsr                    @ Save current mode (SVC) in r1
  38     bic     r3, r1, #0x1f               @ Clear all mode bits
  39     orr     r3, r3, #0x16               @ Set bits for Monitor mode
  40     msr     cpsr_cxsf, r3               @ We are now in Monitor Mode
  41
  42     mov     sp, r0                      @ Use the passed sp
  43     mov     lr, r2                      @ Use the same lr as before
  44
  45     msr     spsr_cxsf, r1               @ Use saved mode for the MOVS jump to the kernel
  46     bx      lr
  47
  48 # We cannot use the instruction 'movs pc, lr' because the caller can be written either in ARM or Thumb2 assembler.
  49 # When we will jump into this function, we will set the CPSR flag to ARM assembler. By copying directly 'lr' into
  50 # 'pc'; we will not change the CPSR flag and it will crash.
  51 # The way to fix this limitation is to do the movs into the ARM assmbler code and then do a 'bx'.
  52 ASM_PFX(return_from_exception):
  53     ldr     lr, returned_exception
  54
  55     #The following instruction breaks the code.
  56     #movs    pc, lr
  57     mrs     r2, cpsr
  58     bic     r2, r2, #0x1f
  59     orr     r2, r2, #0x13
  60     msr     cpsr_c, r2
  61
  62 returned_exception:                           @ We are now in non-secure state
  63     bx      r0
  64
  65 # Save the current Program Status Register (PSR) into the Saved PSR
  66 ASM_PFX(copy_cpsr_into_spsr):
  67     mrs     r0, cpsr
  68     msr     spsr_cxsf, r0
  69     bx      lr
  70
  71 dead:
  72     b       dead
  73
  74 ASM_FUNCTION_REMOVE_IF_UNREFERENCED