feat: returning from permute mode as user

assembleur.s

@@ -6,12 +6,13 @@
 #include "globals.h"
 
 .global asm_test_fault
+.global reset_user_stack
 .global switch_to_user_mode
 .global switch_to_supervisor_mode
 .global change_ret
 .extern user_stack DATA				// this adress can be read like: ldr Rx, =user_stack
 
-switch_to_user_mode:
+reset_user_stack:
 	ldr r0, =user_stack
 	add r0, r0, #8192 				// 2048 * word_size
 	msr PSP, r0
@@ -20,9 +21,16 @@ switch_to_user_mode:
 	isb
 	bx  lr
 
+switch_to_user_mode:
+	mrs r0, control
+	mov r0, #3
+	msr control, r0
+	isb
+	bx lr
+
 switch_to_supervisor_mode:
 	mrs r0, control
-	mov r0, #2
+	mov r0, #0
 	msr control, r0
 	isb
 	bx lr

mpu_user_console_etu.c

@@ -36,6 +36,7 @@ unsigned arr_err_code[BUF_SIZE] = { 0 };
 volatile static unsigned idx_error;
 extern bool is_supervisor_mode;
 
+void reset_user_stack();
 void switch_to_user_mode();
 void asm_test_fault();
 void change_ret(void *addr);
@@ -61,13 +62,15 @@ void test_supervisor_mode() {
 	a = *p_out_of_mem;		// not OK (out of regions)
 }
 
-void svc_call(void) {
-	char buff[64];
-	printf("Current: %s\nType 'switch' to toggle between USER and SUPERVISOR: ", is_supervisor_mode?"Supervisor":"User");
+void permute_mode(void) {
+	char buff[64] = { 0 };
+	printf("Current: %s\nType 'switch' to toggle between USER and SUPERVISOR: ",
+			is_supervisor_mode ? "Supervisor" : "User");
 	fflush(stdin);
 	fscanf(stdin, "%s", buff);
 
-	if (strncmp(buff, "switch", 64) == 0){
+	char cmd[] = "switch";
+	if (strncmp(buff, cmd, strlen(cmd)) == 0) {
 		if (!is_supervisor_mode) { 	// If user mode
 			__asm volatile ("svc 0x32");
 		} else {					// If supervisor
@@ -75,8 +78,7 @@ void svc_call(void) {
 		}
 		is_supervisor_mode = !is_supervisor_mode;
 	}
-	printf("Current: %s\n", is_supervisor_mode?"Supervisor":"User");
-
+	printf("Current: %s\n", is_supervisor_mode ? "Supervisor" : "User");
 }
 
 void test_user_mode() {
@@ -100,7 +102,6 @@ int main(void) {
 	MPU->RBAR = 0x00000000;
 	MPU->RASR = RO | BTEX_NORMAL_NOT_SHAREABLE | SET_SIZE_512KB | REGION_ENABLE;
 
-
 	// Region 1 (SRAM1)
 	MPU->RNR = 1;
 	MPU->RBAR = 0x10000000;
@@ -137,13 +138,13 @@ int main(void) {
 
 	user_start: user_stating_address = &&user_start;// save the address of the label 'user_start' (for exercise 2)
 
-	switch_to_user_mode();					// to be implemented
+	reset_user_stack();					// to be implemented
 
 	// testing memory accesses in user mode:
 	//test_user_mode();		// to be removed after checking
 
 	while (1) {
-		svc_call();
+		permute_mode();
 		exec_user_read_write();
 	}