libsecureshield: add securshield_excpt_bit_clear

this function is used to clear the internal protection bit of exception regs (ECR, BTA, ERRET)

Author: Wayne Ren

arc/startup/arc_startup.s

@@ -46,7 +46,7 @@
 #define __ASSEMBLY__
 #include "arc.h"
 
-.file "arc_startup.s"
+	.file "arc_startup.s"
 
 .weak	_f_sdata		/* start of small data, defined in link script */
 .weak	init_hardware_hook	/* app hardware init hook */
@@ -205,6 +205,9 @@ _arc_reset_call_main:
 	/* init cache */
 	jl	arc_cache_init
 	jl 	secureshield_start
+#if SECURESHIELD_VERSION == 2
+	jl 	secureshield_except_bit_clear
+#endif
 #else
 /* early init of interrupt and exception */
 	jl	exc_int_init
@@ -229,7 +232,7 @@ _arc_reset_call_main:
 	.align 4
 _exit_halt:
 _exit_loop:
-	flag	0x1
+	flag	AUX_STATUS_MASK_HALT
 	nop
 	nop
 	nop

library/secureshield/export/inc/secureshield_sys_ops_exports.h

@@ -46,6 +46,8 @@ extern void secureshield_perf_start(void);
 extern uint32_t secureshield_perf_end(void);
 #elif SECURESHIELD_VERSION == 2
 
+extern void secureshield_except_bit_clear(void);
+
 #endif
 
 extern uint32_t secureshield_arc_lr_reg(uint32_t addr);

library/secureshield/export/src/sys_ops.c

@@ -102,4 +102,32 @@ int32_t secureshield_container_id_caller(void)
 {
 	return SECURESHIELD_SECURE_CALL(SECURESHIELD_SECURE_CALL_SYS, "", SECURESHIELD_SYS_CONTAINER_ID_CALLER);
 }
+
+static void temp_trap_handler(void)
+{
+
+}
+
+/**
+ * \brief       
+ * The exception state registers (ERET, ECR, ERSTATUS, ERBTA, EFA, ESYN) will be protected by a new internal bit.
+ * This will be set on exception entry if the exception is triggered on a secure mode instruction and cleared on 
+ * exception entry if the exception is triggered on a non-secure instruction. If set, this bit will prevent 
+ * read/write access to these registers from non-secure mode. Any attempt to access these registers in NS mode 
+ * while protected will result in an EV_PriviligeV exception.
+ * 
+ * this function is used to clear this bit.
+ */
+void secureshield_except_bit_clear(void) 
+{
+    EXC_HANDLER prev_trap_handler;
+
+    exc_nest_count = 1;
+    prev_trap_handler = exc_handler_get(EXC_NO_TRAP);
+    exc_handler_install(EXC_NO_TRAP, (EXC_HANDLER)temp_trap_handler);
+    Asm("trap_s 0");
+    exc_nest_count = 0;
+    exc_handler_install(EXC_NO_TRAP, prev_trap_handler);
+}
+
 #endif