1 files changed, 74 insertions, 0 deletions
diff --git a/ArmPlatformPkg/Sec/Helper.S b/ArmPlatformPkg/Sec/Helper.S
new file mode 100644
index 0000000000..94bd68f8bc
--- /dev/null
+++ b/ArmPlatformPkg/Sec/Helper.S
@@ -0,0 +1,74 @@
+#========================================================================================
+#  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.             
+#
+#=======================================================================================
+
+#start of the code section
+.text 
+.align 3
+
+GCC_ASM_EXPORT(monitor_vector_table)
+GCC_ASM_EXPORT(return_from_exception)
+GCC_ASM_EXPORT(enter_monitor_mode)
+GCC_ASM_EXPORT(copy_cpsr_into_spsr)
+
+ASM_PFX(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
+ASM_PFX(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'.
+ASM_PFX(return_from_exception):
+    ldr     lr, returned_exception
+
+    #The following instruction breaks the code.
+    #movs    pc, lr
+    mrs     r2, cpsr
+    bic     r2, r2, #0x1f
+    orr     r2, r2, #0x13
+    msr     cpsr_c, r2
+
+returned_exception:                           @ We are now in non-secure state
+    bx      r0
+
+# Save the current Program Status Register (PSR) into the Saved PSR
+ASM_PFX(copy_cpsr_into_spsr):
+    mrs     r0, cpsr
+    msr     spsr_cxsf, r0
+    bx      lr
+
+dead:
+    B       dead
+    
+.end