From b3f915dcb55fa4dd59cf99d2b20703a451506ca8 Mon Sep 17 00:00:00 2001
From: vhaudiquet <vhaudiquet343@hotmail.fr>
Date: Fri, 20 Oct 2023 12:02:50 +0200
Subject: [PATCH] CPU privilege modes

---
 src/cpu/rv32cpu.c |  7 +++++--
 src/cpu/rv32cpu.h | 25 +++++++++++++++++--------
 2 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/src/cpu/rv32cpu.c b/src/cpu/rv32cpu.c
index aab926a..d4fbede 100644
--- a/src/cpu/rv32cpu.c
+++ b/src/cpu/rv32cpu.c
@@ -45,6 +45,7 @@ void cpu_init()
 	pthread_mutex_init(&cpu0_mutex, 0);
 	pthread_cond_init(&cpu0->sim_condition, 0);
 	cpu0->regs.zero = 0;
+	cpu0->privilege_mode = MACHINE;
 }
 
 static void cpu_decode(raw_instruction_t raw_instruction, instruction_t* output)
@@ -523,8 +524,10 @@ static void cpu_execute(rv32_cpu_t* cpu, instruction_t* instruction)
 							fprintf(stderr, "SRET: We don't support that.\n");
 							break;
 						case IMM_MRET:
-							// Act like a normal ret/jalr, with destination address being CSR_MEPC content
-							fprintf(stderr, "Warning: MRET: We don't support privilege mode change\n");
+							// Ret to destination address : CSR_MEPC content
+							// Change privilege mode to SUPERVISOR
+							// TODO : Pop lower-privilege interrupt enable and privilege mode stack
+							cpu->privilege_mode = SUPERVISOR;
 							cpu->pc = cpu->csr[CSR_MEPC] - 4;
 							break;
 						default:
diff --git a/src/cpu/rv32cpu.h b/src/cpu/rv32cpu.h
index b648843..f6248ed 100644
--- a/src/cpu/rv32cpu.h
+++ b/src/cpu/rv32cpu.h
@@ -7,13 +7,20 @@
 
 #include "csr.h"
 
+typedef enum RVCPU_PRIVILEGE_MODE
+{
+	USER,
+	SUPERVISOR,
+	MACHINE
+} rvcpu_privilege_mode_t;
+
 /*
-* This is a structure encoding for the registers of
-* the rv32 cpu.
-* It allows access of register x0 using :
-* structname.x0, structname.zero, structname.x[0]
-* This way, access can be really flexible
-*/
+ * This is a structure encoding for the registers of
+ * the rv32 cpu.
+ * It allows access of register x0 using :
+ * structname.x0, structname.zero, structname.x[0]
+ * This way, access can be really flexible
+ */
 typedef struct RV32_CPU_REGS
 {
 	union
@@ -188,10 +195,12 @@ typedef struct RV32_CPU_REGS
 typedef struct RV32_CPU
 {
 	// CPU values
-    rv32_cpu_regs_t regs;
-    uint32_t pc;
+	rv32_cpu_regs_t regs;
+	uint32_t pc;
 	uint32_t csr[CSR_COUNT];
 
+	rvcpu_privilege_mode_t privilege_mode;
+
 	// Simulation data
 	ssize_t sim_ticks_left; // -1 : simulate forever
 	size_t sim_ticks_done;