arc: add user mode support. fix the issue in the memory_protection example

there was an issue caused by stack checking when switch from kernel mode
to user mode. The issue is solved by disable stack checking.

Signed-off-by: Yuguo Zou <yuguo.zou@synopsys.com>

Author: YuguoWH

arc/arc_util.s

@@ -34,21 +34,60 @@
 
 	.file "arc_utils.s"
 
-	.text
-	.global arc_in_user_mode
-	.align 4
-arc_in_user_mode:
-	lr r0, [AUX_STATUS32]
-	bbit1 r0, 20, 1f
-	bset r1, r0, 20
-	bclr r1, r1, 31
-	kflag r1
-	lr r1, [AUX_STATUS32]
-	bbit0 r1, 20, 2f
-	kflag r0
-1:
-	j_s.d [blink]
-	mov r0, 0
-2:
-	j_s.d [blink]
-	mov r0, 1
+/**
+ * @brief Go to user mode
+ *
+ * @param target Target address to run in user mode, 0 means next
+ *               line of code
+ * @param sp Stack where the target address runs, 0 means using
+ *           current stack
+ */
+    .text
+    .global arc_goto_usermode
+    .align 4
+arc_goto_usermode:
+    cmp r0, 0
+    mov.z   r0, blink
+    cmp r1, 0
+    mov.nz  sp, r1
+#if defined(ARC_FEATURE_SEC_PRESENT)
+    sr  (1 << AUX_ERSEC_STAT_BIT_ERM), [AUX_ERSEC_STAT]
+    sr  sp, [AUX_SEC_U_SP]
+#else
+    sr  sp, [AUX_USER_SP]
+#endif
+    lr  r1, [AUX_STATUS32]
+    bset    r1, r1, AUX_STATUS_BIT_U
+    sr  r1, [AUX_ERSTATUS]
+    lr  r1, [AUX_STATUS32]
+    bset    r1, r1, AUX_STATUS_BIT_AE
+    kflag   r1
+    sr  r0, [AUX_ERRET]
+    rtie
+
+/**
+ * @brief go to kernel mode
+ * this function uses trap exception to do switch from user mode to kernel mode,
+ * please install exc_entry_arc_goto_kernelmode for trap exception before call this
+ * function
+ * @param target, the target address to run in kernel mode, 0 means next line of code
+ * @param sp, the stack where the target address runs, 0 means using current stack
+ */
+    .text
+    .global arc_goto_kernelmode
+    .global exc_entry_arc_goto_kernelmode
+    .align 4
+arc_goto_kernelmode:
+    cmp r0, 0
+    mov.z   r0, blink
+    cmp r1, 0
+    mov.z   r1, sp
+    trap_s  0
+    .align 4
+exc_entry_arc_goto_kernelmode:
+    mov sp, r1
+    sr  r0, [AUX_ERRET]
+    lr  r0, [AUX_ERSTATUS]
+    bclr    r0, r0, AUX_STATUS_BIT_U
+    sr  r0, [AUX_ERSTATUS]
+    rtie

example/baremetal/arc_feature/memory_protection/main.c

@@ -92,7 +92,7 @@ static void user_mode_func(void)
 	arc_kflag(0);
 	arc_goto_kernelmode(0, 0);
 
-	EMBARC_PRINTF("end of program\r\n");
+	EMBARC_PRINTF("Memory Protection Test Done\n");
 	while (1) {
 		;
 	}
@@ -292,7 +292,12 @@ int main(void)
 	EMBARC_PRINTF("raise violation of execute in RAM \r\n");
 	trigger_execute_violation((uint32_t)_f_data);
 	EMBARC_PRINTF("go to user mode \r\n");
+#if	ARC_FEATURE_STACK_CHECK
+	// disable stack check
+	arc_stack_check_disable();
+#endif
 	arc_goto_usermode(user_mode_func, &user_mode_stack[512]);
+	// arc_goto_usermode() does NOT return
 #else /* ARC_FEATURE_MPU_PRESENT */
 	EMBARC_PRINTF("This example is not supported under current configurations \r\n");
 #endif /* ARC_FEATURE_MPU_PRESENT */

include/arc/arc.h

@@ -560,11 +560,6 @@ extern "C" {
 #endif
 
 /* add type definition and function declaration here */
-/**
- * \brief check whether process is in user mode
- * \retval 0 kernel mode, 1 user mode
- */
-extern unsigned int arc_in_user_mode(void);
 
 #ifdef __cplusplus
 }

include/arc/arc_builtin.h

@@ -379,6 +379,93 @@ Inline uint32_t arc_core_id(void)
 	return ret;
 }
 
+/**
+ * @fn void arc_stack_check_disable(void)
+ * @brief Disable hardware stack checking
+ */
+Inline void arc_stack_check_disable(void)
+{
+#if ARC_FEATURE_SEC_PRESENT
+  Asm(
+    "bclr %0, %0, %1\n"
+    "sflag %%r0\n"
+    :
+    : "r" (arc_aux_read(AUX_SEC_STAT)), "i" (AUX_SEC_STAT_BIT_SSC));
+#else
+  Asm(
+    "bclr %0, %0, %1\n"
+    "kflag %%r0\n"
+    :
+    : "r" (arc_aux_read(AUX_STATUS32)), "i" (AUX_STATUS_BIT_SC));
+#endif
+}
+
+/**
+ * @fn void arc_kernel_stack_check_configure(uint32_t top, uint32_t base)
+ * @brief Configure stack checking in kernel mode
+ *
+ * @param top Top of stack
+ * @param base Base of stack
+ */
+Inline void arc_kernel_stack_check_configure(uint32_t top, uint32_t base)
+{
+#if ARC_FEATURE_SEC_PRESENT
+  arc_aux_write(AUX_S_KSTACK_TOP, top);
+  arc_aux_write(AUX_S_KSTACK_BASE, base);
+#else
+  arc_aux_write(AUX_KSTACK_TOP, top);
+  arc_aux_write(AUX_KSTACK_BASE, base);
+#endif
+}
+
+/**
+ * @fn uint32_t arc_is_user_mode(void)
+ * @brief Check whether processor is in user mode
+ * this function relies on AUX_STATUS_BIT_US set in privileged mode first
+ * @return 1 user mode, 0 privileged mode
+ */
+Inline uint32_t arc_in_user_mode(void)
+{
+  uint32_t status;
+
+  Asm(
+    "lr %0, [%1]\n"
+    : "=r" (status)
+    : "i" (AUX_STATUS32)
+    : "memory");
+
+  return !(status & AUX_STATUS_MASK_US) ? 1 : 0;
+}
+
+/**
+ * @brief Go to user mode
+ * It's suggested to disable interrupt before call this function especially
+ * when using current stack, i.e., sp == 0. Because interrupt handling requires
+ * kernel mode stack which is different with user mode stack.
+ * @param target Target address to run in user mode, 0 means next
+ *               line of code
+ * @param sp Stack where the target address runs, 0 means using
+ *           current stack
+ */
+extern void arc_goto_usermode(void *target, uint32_t *sp);
+
+/**
+ * @brief Go to kernel mode
+ * this function uses trap exception to do switch from user mode to kernel mode,
+ * please install exc_entry_arc_goto_kernelmode for trap exception before call this
+ * function
+ * @param target Target address to run in kernel mode, 0 means next line of code
+ * @param sp Stack where the target address runs, 0 means using current stack
+ */
+extern void arc_goto_kernelmode(void *target, uint32_t *sp);
+
+/**
+ * @brief Trap exception entry used for arc_goto_kernelmode
+ *
+ * install this entry for trap exception before call arc_goto_kernelmode
+ */
+extern void exc_entry_arc_goto_kernelmode(void);
+
 #ifdef __cplusplus
 }
 #endif