Added MRET/SRET mock support

src/cpu/rv32cpu.c

@@ -518,6 +518,12 @@ static void cpu_execute(rv32_cpu_t* cpu, instruction_t* instruction)
 							cpu->sim_ticks_left = 1;
 							cpu->pc -= 4;
 							break;
+						case IMM_SRET:
+							fprintf(stderr, "SRET: We don't support that.\n");
+							break;
+						case IMM_MRET:
+							fprintf(stderr, "MRET: We don't support that.\n");
+							break;
 						default:
 							switch(instruction->func7)
 							{
@@ -1070,6 +1076,12 @@ static void cpu_print_instruction(instruction_t* instruction)
 						case IMM_EBREAK:
 							printf("ebreak\n");
 							break;
+						case IMM_SRET:
+							printf("sret\n");
+							break;
+						case IMM_MRET:
+							printf("mret\n");
+							break;
 						default:
 							switch(instruction->func7)
 							{