Add ArmPlatformPkg from ARM Ltd. patch.

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

diff --git a/ArmPlatformPkg/Sec/Helper.S b/ArmPlatformPkg/Sec/Helper.S
new file mode 100644 (file)
index 0000000..94bd68f
--- /dev/null
+++ b/ArmPlatformPkg/Sec/Helper.S
@@ -0,0 +1,74 @@
+#========================================================================================\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
+#start of the code section\r
+.text \r
+.align 3\r
+\r
+GCC_ASM_EXPORT(monitor_vector_table)\r
+GCC_ASM_EXPORT(return_from_exception)\r
+GCC_ASM_EXPORT(enter_monitor_mode)\r
+GCC_ASM_EXPORT(copy_cpsr_into_spsr)\r
+\r
+ASM_PFX(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
+ASM_PFX(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
+ASM_PFX(return_from_exception):\r
+    ldr     lr, returned_exception\r
+\r
+    #The following instruction breaks the code.\r
+    #movs    pc, lr\r
+    mrs     r2, cpsr\r
+    bic     r2, r2, #0x1f\r
+    orr     r2, r2, #0x13\r
+    msr     cpsr_c, r2\r
+\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
+ASM_PFX(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