MRET jump support

src/cpu/rv32cpu.c

@@ -522,7 +522,9 @@ static void cpu_execute(rv32_cpu_t* cpu, instruction_t* instruction)
 							fprintf(stderr, "SRET: We don't support that.\n");
 							break;
 						case IMM_MRET:
-							fprintf(stderr, "MRET: We don't support that.\n");
+							// 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");
+							cpu->pc = cpu->csr[CSR_MEPC] - 4;
 							break;
 						default:
 							switch(instruction->func7)