arch: aarch32: cortex_m/r: Add arch helper function

Create z_arm_thread_is_user_mode to abstract the implementation
differences between Cortex-M and R to determine if the current thread is
in user or kernel mode.

Signed-off-by: Bradley Bolen <bbolen@lexmark.com>

arch/arm/core/aarch32/cortex_a_r/CMakeLists.txt

@@ -13,3 +13,5 @@ zephyr_library_sources(
   stacks.c
   tcm.c
   )
+
+zephyr_library_sources_ifdef(CONFIG_USERSPACE thread.c)

arch/arm/core/aarch32/cortex_a_r/thread.c

@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2021 Lexmark International, Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <stdbool.h>
+#include <arch/arm/aarch32/cortex_a_r/cmsis.h>
+
+bool z_arm_thread_is_in_user_mode(void)
+{
+	uint32_t value;
+
+	/*
+	 * For Cortex-R, the mode (lower 5) bits will be 0x10 for user mode.
+	 */
+	value = __get_CPSR();
+	return ((value & CPSR_M_Msk) == CPSR_M_USR);
+}

arch/arm/core/aarch32/cortex_m/CMakeLists.txt

@@ -14,6 +14,7 @@ zephyr_library_sources(
   thread_abort.c
   )
 
+zephyr_library_sources_ifdef(CONFIG_USERSPACE thread.c)
 zephyr_library_sources_ifdef(CONFIG_DEBUG_COREDUMP coredump.c)
 zephyr_library_sources_ifdef(CONFIG_THREAD_LOCAL_STORAGE __aeabi_read_tp.S)
 

arch/arm/core/aarch32/cortex_m/thread.c

@@ -0,0 +1,17 @@
+/*
+ * Copyright (c) 2021 Lexmark International, Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <stdbool.h>
+#include <arch/arm/aarch32/cortex_m/cmsis.h>
+
+bool z_arm_thread_is_in_user_mode(void)
+{
+	uint32_t value;
+
+	/* return mode information */
+	value = __get_CONTROL();
+	return (value & CONTROL_nPRIV_Msk) != 0;
+}

arch/arm/core/aarch32/thread.c

@@ -396,7 +396,7 @@ uint32_t z_check_thread_stack_fail(const uint32_t fault_addr, const uint32_t psp
 #if defined(CONFIG_USERSPACE)
 	if (thread->arch.priv_stack_start) {
 		/* User thread */
-		if ((__get_CONTROL() & CONTROL_nPRIV_Msk) == 0U) {
+		if (z_arm_thread_is_in_user_mode() == false) {
 			/* User thread in privilege mode */
 			if (IS_MPU_GUARD_VIOLATION(
 				thread->arch.priv_stack_start - guard_len,

include/arch/arm/aarch32/misc.h

@@ -31,6 +31,10 @@ static ALWAYS_INLINE void arch_nop(void)
 	__asm__ volatile("nop");
 }
 
+#if defined(CONFIG_USERSPACE)
+extern bool z_arm_thread_is_in_user_mode(void);
+#endif
+
 #endif
 
 #ifdef __cplusplus

include/arch/arm/aarch32/syscall.h

@@ -26,7 +26,7 @@
 
 #include <zephyr/types.h>
 #include <stdbool.h>
-#include <arch/arm/aarch32/cortex_m/cmsis.h>
+#include <arch/arm/aarch32/misc.h>
 
 #ifdef __cplusplus
 extern "C" {
@@ -165,6 +165,7 @@ static inline uintptr_t arch_syscall_invoke0(uintptr_t call_id)
 
 static inline bool arch_is_user_context(void)
 {
+#if defined(CONFIG_CPU_CORTEX_M)
 	uint32_t value;
 
 	/* check for handler mode */
@@ -172,10 +173,9 @@ static inline bool arch_is_user_context(void)
 	if (value) {
 		return false;
 	}
+#endif
 
-	/* if not handler mode, return mode information */
+	return z_arm_thread_is_in_user_mode();
-	__asm__ volatile("mrs %0, CONTROL\n\t" : "=r"(value));
-	return (value & CONTROL_nPRIV_Msk) ? true : false;
 }
 
 #ifdef __cplusplus