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 # r0: Monitor World EntryPoint
  24 # r1: MpId
  25 # r2: Secure Monitor mode stack
  26 ASM_PFX(enter_monitor_mode):
  27     mrs     r4, cpsr                    @ Save current mode (SVC) in r1
  28     bic     r3, r4, #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     cmp     r2, #0                      @ If a Secure Monitor stack base has been passed, used it
  33     movne   sp, r2                      @ Use the passed sp
  34
  35     mov     lr, r0                      @ Use the pass entrypoint as lr
  36
  37     msr     spsr_cxsf, r4               @ Use saved mode for the MOVS jump to the kernel
  38
  39     mov     r4, r0                      @ Swap EntryPoint and MpId registers
  40     mov     r0, r1
  41
  42     bx      r4
  43
  44 # We cannot use the instruction 'movs pc, lr' because the caller can be written either in ARM or Thumb2 assembler.
  45 # When we will jump into this function, we will set the CPSR flag to ARM assembler. By copying directly 'lr' into
  46 # 'pc'; we will not change the CPSR flag and it will crash.
  47 # The way to fix this limitation is to do the movs into the ARM assmbler code and then do a 'bx'.
  48 ASM_PFX(return_from_exception):
  49     ldr     lr, returned_exception
  50
  51     #The following instruction breaks the code.
  52     #movs    pc, lr
  53     mrs     r2, cpsr
  54     bic     r2, r2, #0x1f
  55     orr     r2, r2, #0x13
  56     msr     cpsr_c, r2
  57
  58 returned_exception:                           @ We are now in non-secure state
  59     bx      r0
  60
  61 # Save the current Program Status Register (PSR) into the Saved PSR
  62 ASM_PFX(copy_cpsr_into_spsr):
  63     mrs     r0, cpsr
  64     msr     spsr_cxsf, r0
  65     bx      lr
  66
  67 # Set the Non Secure Mode
  68 ASM_PFX(set_non_secure_mode):
  69     push    { r1 }
  70     and     r0, r0, #0x1f     @ Keep only the mode bits
  71     mrs     r1, spsr          @ Read the spsr
  72     bic     r1, r1, #0x1f     @ Clear all mode bits
  73     orr     r1, r1, r0
  74     msr     spsr_cxsf, r1     @ write back spsr (may have caused a mode switch)
  75     isb
  76     pop     { r1 }
  77     bx      lr                @ return (hopefully thumb-safe!)
  78
  79 dead:
  80     b       dead
  81
  82 ASM_FUNCTION_REMOVE_IF_UNREFERENCED