ArmPlatformPkg: Move the Secure Monitor initialization into a separate 'ArmTrustedMon...
[mirror_edk2.git] / 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