cd9603c7a02370cd613b3ffad8aab42760af8e03
[mirror_edk2.git] / 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 EXPORT set_non_secure_mode
19
20 AREA Helper, CODE, READONLY
21
22 ALIGN 32
23 monitor_vector_table
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 ldr pc, dead
32
33 // arg0: Secure Monitor mode stack
34 enter_monitor_mode
35 mov r2, lr // Save current lr
36
37 mrs r1, cpsr // Save current mode (SVC) in r1
38 bic r3, r1, #0x1f // Clear all mode bits
39 orr r3, r3, #0x16 // Set bits for Monitor mode
40 msr cpsr_cxsf, r3 // We are now in Monitor Mode
41
42 mov sp, r0 // Use the passed sp
43 mov lr, r2 // Use the same lr as before
44
45 msr spsr_cxsf, r1 // Use saved mode for the MOVS jump to the kernel
46 bx lr
47
48 // We cannot use the instruction 'movs pc, lr' because the caller can be written either in ARM or Thumb2 assembler.
49 // When we will jump into this function, we will set the CPSR flag to ARM assembler. By copying directly 'lr' into
50 // 'pc'; we will not change the CPSR flag and it will crash.
51 // The way to fix this limitation is to do the movs into the ARM assmbler code and then do a 'bx'.
52 return_from_exception
53 adr lr, returned_exception
54 movs pc, lr
55 returned_exception // We are now in non-secure state
56 bx r0
57
58 // Save the current Program Status Register (PSR) into the Saved PSR
59 copy_cpsr_into_spsr
60 mrs r0, cpsr
61 msr spsr_cxsf, r0
62 bx lr
63
64 // Set the Non Secure Mode
65 set_non_secure_mode
66 push { r1 }
67 and r0, r0, #0x1f // Keep only the mode bits
68 mrs r1, spsr // Read the spsr
69 bic r1, r1, #0x1f // Clear all mode bits
70 orr r1, r1, r0
71 msr spsr_cxsf, r1 // write back spsr (may have caused a mode switch)
72 isb
73 pop { r1 }
74 bx lr // return (hopefully thumb-safe!)
75
76 dead
77 B dead
78
79 END