ArmPlatformPkg/Sec/Arm/Helper.asm

   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     EXPORT  return_from_exception
  15     EXPORT  enter_monitor_mode
  16     EXPORT  copy_cpsr_into_spsr
  17     EXPORT  set_non_secure_mode
  18
  19     AREA   Helper, CODE, READONLY
  20
  21 // r0: Monitor World EntryPoint
  22 // r1: MpId
  23 // r2: SecBootMode
  24 // r3: Secure Monitor mode stack
  25 enter_monitor_mode FUNCTION
  26     cmp     r3, #0                      // If a Secure Monitor stack base has not been defined then use the Secure stack
  27     moveq   r3, sp
  28
  29     mrs     r4, cpsr                    // Save current mode (SVC) in r4
  30     bic     r5, r4, #0x1f               // Clear all mode bits
  31     orr     r5, r5, #0x16               // Set bits for Monitor mode
  32     msr     cpsr_cxsf, r5               // We are now in Monitor Mode
  33
  34     mov     sp, r3                      // Set the stack of the Monitor Mode
  35
  36     mov     lr, r0                      // Use the pass entrypoint as lr
  37
  38     msr     spsr_cxsf, r4               // Use saved mode for the MOVS jump to the kernel
  39
  40     mov     r4, r0                      // Swap EntryPoint and MpId registers
  41     mov     r0, r1
  42     mov     r1, r2
  43     mov     r2, r3
  44
  45     bx      r4
  46     ENDFUNC
  47
  48 // Return-from-exception is not an interworking return, so we must do it
  49 // in two steps, in case r0 has the Thumb bit set.
  50 return_from_exception
  51     adr     lr, returned_exception
  52     movs    pc, lr
  53 returned_exception                           // We are now in non-secure state
  54     bx      r0
  55
  56 // Save the current Program Status Register (PSR) into the Saved PSR
  57 copy_cpsr_into_spsr
  58     mrs     r0, cpsr
  59     msr     spsr_cxsf, r0
  60     bx      lr
  61
  62 // Set the Non Secure Mode
  63 set_non_secure_mode
  64     push    { r1 }
  65     and     r0, r0, #0x1f     // Keep only the mode bits
  66     mrs     r1, spsr          // Read the spsr
  67     bic     r1, r1, #0x1f     // Clear all mode bits
  68     orr     r1, r1, r0
  69     msr     spsr_cxsf, r1     // write back spsr (may have caused a mode switch)
  70     isb
  71     pop     { r1 }
  72     bx      lr                // return (hopefully thumb-safe!)
  73
  74 dead
  75     B       dead
  76
  77     END