1 files changed, 66 insertions, 0 deletions
diff --git a/ArmPlatformPkg/Sec/Helper.asm b/ArmPlatformPkg/Sec/Helper.asm
new file mode 100644
index 0000000000..43a0749138
--- /dev/null
+++ b/ArmPlatformPkg/Sec/Helper.asm
@@ -0,0 +1,66 @@
+//
+//  Copyright (c) 2011, ARM Limited. All rights reserved.
+//  
+//  This program and the accompanying materials                          
+//  are licensed and made available under the terms and conditions of the BSD License         
+//  which accompanies this distribution.  The full text of the license may be found at        
+//  http://opensource.org/licenses/bsd-license.php                                            
+//
+//  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,                     
+//  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.             
+//
+//
+
+    EXPORT  monitor_vector_table
+    EXPORT  return_from_exception
+    EXPORT  enter_monitor_mode
+    EXPORT  copy_cpsr_into_spsr
+    
+    AREA   Helper, CODE, READONLY
+
+    ALIGN 32
+monitor_vector_table
+    ldr pc, dead
+    ldr pc, dead
+    ldr pc, dead
+    ldr pc, dead
+    ldr pc, dead
+    ldr pc, dead
+    ldr pc, dead
+    ldr pc, dead
+
+// arg0: Secure Monitor mode stack
+enter_monitor_mode
+    mov     r2, lr                      // Save current lr
+
+    mrs     r1, cpsr                    // Save current mode (SVC) in r1
+    bic     r3, r1, #0x1f               // Clear all mode bits
+    orr     r3, r3, #0x16               // Set bits for Monitor mode
+    msr     cpsr_cxsf, r3               // We are now in Monitor Mode
+
+    mov     sp, r0                      // Use the passed sp
+    mov     lr, r2                      // Use the same lr as before
+    
+    msr     spsr_cxsf, r1               // Use saved mode for the MOVS jump to the kernel
+    bx      lr
+
+// We cannot use the instruction 'movs pc, lr' because the caller can be written either in ARM or Thumb2 assembler.
+// When we will jump into this function, we will set the CPSR flag to ARM assembler. By copying directly 'lr' into
+// 'pc'; we will not change the CPSR flag and it will crash.
+// The way to fix this limitation is to do the movs into the ARM assmbler code and then do a 'bx'.
+return_from_exception
+    adr     lr, returned_exception
+    movs    pc, lr
+returned_exception                           // We are now in non-secure state
+    bx      r0
+
+// Save the current Program Status Register (PSR) into the Saved PSR
+copy_cpsr_into_spsr
+    mrs     r0, cpsr
+    msr     spsr_cxsf, r0
+    bx      lr
+
+dead
+    B       dead
+    
+    END