ArmPlatformPkg/Sec/Helper.S

   1 #========================================================================================
   2 #  Copyright (c) 2011-2012, 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(return_from_exception)
  19 GCC_ASM_EXPORT(enter_monitor_mode)
  20 GCC_ASM_EXPORT(copy_cpsr_into_spsr)
  21 GCC_ASM_EXPORT(set_non_secure_mode)
  22
  23 # arg0: Secure Monitor mode stack
  24 ASM_PFX(enter_monitor_mode):
  25     mov     r2, lr                      @ Save current lr
  26
  27     mrs     r1, cpsr                    @ Save current mode (SVC) in r1
  28     bic     r3, r1, #0x1f               @ Clear all mode bits
  29     orr     r3, r3, #0x16               @ Set bits for Monitor mode
  30     msr     cpsr_cxsf, r3               @ We are now in Monitor Mode
  31
  32     mov     sp, r0                      @ Use the passed sp
  33     mov     lr, r2                      @ Use the same lr as before
  34
  35     msr     spsr_cxsf, r1               @ Use saved mode for the MOVS jump to the kernel
  36     bx      lr
  37
  38 # We cannot use the instruction 'movs pc, lr' because the caller can be written either in ARM or Thumb2 assembler.
  39 # When we will jump into this function, we will set the CPSR flag to ARM assembler. By copying directly 'lr' into
  40 # 'pc'; we will not change the CPSR flag and it will crash.
  41 # The way to fix this limitation is to do the movs into the ARM assmbler code and then do a 'bx'.
  42 ASM_PFX(return_from_exception):
  43     ldr     lr, returned_exception
  44
  45     #The following instruction breaks the code.
  46     #movs    pc, lr
  47     mrs     r2, cpsr
  48     bic     r2, r2, #0x1f
  49     orr     r2, r2, #0x13
  50     msr     cpsr_c, r2
  51
  52 returned_exception:                           @ We are now in non-secure state
  53     bx      r0
  54
  55 # Save the current Program Status Register (PSR) into the Saved PSR
  56 ASM_PFX(copy_cpsr_into_spsr):
  57     mrs     r0, cpsr
  58     msr     spsr_cxsf, r0
  59     bx      lr
  60
  61 # Set the Non Secure Mode
  62 ASM_PFX(set_non_secure_mode):
  63     push    { r1 }
  64     and     r0, r0, #0x1f     @ Keep only the mode bits
  65     mrs     r1, spsr          @ Read the spsr
  66     bic     r1, r1, #0x1f     @ Clear all mode bits
  67     orr     r1, r1, r0
  68     msr     spsr_cxsf, r1     @ write back spsr (may have caused a mode switch)
  69     isb
  70     pop     { r1 }
  71     bx      lr                @ return (hopefully thumb-safe!)
  72
  73 dead:
  74     b       dead
  75
  76 ASM_FUNCTION_REMOVE_IF_UNREFERENCED