ArmPlatformPkg/Sec/Helper.asm

   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     EXPORT  monitor_vector_table
  15     EXPORT  return_from_exception
  16     EXPORT  enter_monitor_mode
  17     EXPORT  copy_cpsr_into_spsr
  18
  19     AREA   Helper, CODE, READONLY
  20
  21     ALIGN 32
  22 monitor_vector_table
  23     ldr pc, dead
  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
  32 // arg0: Secure Monitor mode stack
  33 enter_monitor_mode
  34     mov     r2, lr                      // Save current lr
  35
  36     mrs     r1, cpsr                    // Save current mode (SVC) in r1
  37     bic     r3, r1, #0x1f               // Clear all mode bits
  38     orr     r3, r3, #0x16               // Set bits for Monitor mode
  39     msr     cpsr_cxsf, r3               // We are now in Monitor Mode
  40
  41     mov     sp, r0                      // Use the passed sp
  42     mov     lr, r2                      // Use the same lr as before
  43
  44     msr     spsr_cxsf, r1               // Use saved mode for the MOVS jump to the kernel
  45     bx      lr
  46
  47 // We cannot use the instruction 'movs pc, lr' because the caller can be written either in ARM or Thumb2 assembler.
  48 // When we will jump into this function, we will set the CPSR flag to ARM assembler. By copying directly 'lr' into
  49 // 'pc'; we will not change the CPSR flag and it will crash.
  50 // The way to fix this limitation is to do the movs into the ARM assmbler code and then do a 'bx'.
  51 return_from_exception
  52     adr     lr, returned_exception
  53     movs    pc, lr
  54 returned_exception                           // We are now in non-secure state
  55     bx      r0
  56
  57 // Save the current Program Status Register (PSR) into the Saved PSR
  58 copy_cpsr_into_spsr
  59     mrs     r0, cpsr
  60     msr     spsr_cxsf, r0
  61     bx      lr
  62
  63 dead
  64     B       dead
  65
  66     END