Add ArmPlatformPkg from ARM Ltd. patch.

[mirror_edk2.git] / ArmPlatformPkg / Sec / Helper.asm

diff --git a/ArmPlatformPkg/Sec/Helper.asm b/ArmPlatformPkg/Sec/Helper.asm
new file mode 100644 (file)
index 0000000..43a0749
--- /dev/null
+++ b/ArmPlatformPkg/Sec/Helper.asm
@@ -0,0 +1,66 @@
+//\r
+//  Copyright (c) 2011, ARM Limited. All rights reserved.\r
+//  \r
+//  This program and the accompanying materials                          \r
+//  are licensed and made available under the terms and conditions of the BSD License         \r
+//  which accompanies this distribution.  The full text of the license may be found at        \r
+//  http://opensource.org/licenses/bsd-license.php                                            \r
+//\r
+//  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,                     \r
+//  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.             \r
+//\r
+//\r
+\r
+    EXPORT  monitor_vector_table\r
+    EXPORT  return_from_exception\r
+    EXPORT  enter_monitor_mode\r
+    EXPORT  copy_cpsr_into_spsr\r
+    \r
+    AREA   Helper, CODE, READONLY\r
+\r
+    ALIGN 32\r
+monitor_vector_table\r
+    ldr pc, dead\r
+    ldr pc, dead\r
+    ldr pc, dead\r
+    ldr pc, dead\r
+    ldr pc, dead\r
+    ldr pc, dead\r
+    ldr pc, dead\r
+    ldr pc, dead\r
+\r
+// arg0: Secure Monitor mode stack\r
+enter_monitor_mode\r
+    mov     r2, lr                      // Save current lr\r
+\r
+    mrs     r1, cpsr                    // Save current mode (SVC) in r1\r
+    bic     r3, r1, #0x1f               // Clear all mode bits\r
+    orr     r3, r3, #0x16               // Set bits for Monitor mode\r
+    msr     cpsr_cxsf, r3               // We are now in Monitor Mode\r
+\r
+    mov     sp, r0                      // Use the passed sp\r
+    mov     lr, r2                      // Use the same lr as before\r
+    \r
+    msr     spsr_cxsf, r1               // Use saved mode for the MOVS jump to the kernel\r
+    bx      lr\r
+\r
+// We cannot use the instruction 'movs pc, lr' because the caller can be written either in ARM or Thumb2 assembler.\r
+// When we will jump into this function, we will set the CPSR flag to ARM assembler. By copying directly 'lr' into\r
+// 'pc'; we will not change the CPSR flag and it will crash.\r
+// The way to fix this limitation is to do the movs into the ARM assmbler code and then do a 'bx'.\r
+return_from_exception\r
+    adr     lr, returned_exception\r
+    movs    pc, lr\r
+returned_exception                           // We are now in non-secure state\r
+    bx      r0\r
+\r
+// Save the current Program Status Register (PSR) into the Saved PSR\r
+copy_cpsr_into_spsr\r
+    mrs     r0, cpsr\r
+    msr     spsr_cxsf, r0\r
+    bx      lr\r
+\r
+dead\r
+    B       dead\r
+    \r
+    END\r