Merge pull request #309 from riscv/dret

Fix DRET in M-mode, and change how D-mode is represented

riscv/execute.cc

@@ -85,13 +85,13 @@ static reg_t execute_insn(processor_t* p, reg_t pc, insn_fetch_t fetch)
 
 bool processor_t::slow_path()
 {
-  return debug || state.single_step != state.STEP_NONE || state.dcsr.cause;
+  return debug || state.single_step != state.STEP_NONE || state.debug_mode;
 }
 
 // fetch/decode/execute loop
 void processor_t::step(size_t n)
 {
-  if (state.dcsr.cause == DCSR_CAUSE_NONE) {
+  if (!state.debug_mode) {
     if (halt_request) {
       enter_debug_mode(DCSR_CAUSE_DEBUGINT);
     } // !!!The halt bit in DCSR is deprecated.
@@ -130,7 +130,7 @@ void processor_t::step(size_t n)
         {
           if (unlikely(!state.serialized && state.single_step == state.STEP_STEPPED)) {
             state.single_step = state.STEP_NONE;
-            if (state.dcsr.cause == DCSR_CAUSE_NONE) {
+            if (!state.debug_mode) {
               enter_debug_mode(DCSR_CAUSE_STEP);
               // enter_debug_mode changed state.pc, so we can't just continue.
               break;

riscv/insns/dret.h

@@ -1,9 +1,9 @@
-require_privilege(PRV_M);
+require(STATE.debug_mode);
 set_pc_and_serialize(STATE.dpc);
 p->set_privilege(STATE.dcsr.prv);
 
 /* We're not in Debug Mode anymore. */
-STATE.dcsr.cause = 0;
+STATE.debug_mode = false;
 
 if (STATE.dcsr.step)
   STATE.single_step = STATE.STEP_STEPPING;

riscv/mmu.cc

@@ -51,7 +51,7 @@ reg_t mmu_t::translate(reg_t addr, reg_t len, access_type type)
 
   reg_t mode = proc->state.prv;
   if (type != FETCH) {
-    if (!proc->state.dcsr.cause && get_field(proc->state.mstatus, MSTATUS_MPRV))
+    if (!proc->state.debug_mode && get_field(proc->state.mstatus, MSTATUS_MPRV))
       mode = get_field(proc->state.mstatus, MSTATUS_MPP);
   }
 

riscv/processor.cc

@@ -277,7 +277,7 @@ void processor_t::take_interrupt(reg_t pending_interrupts)
   if (enabled_interrupts == 0)
     enabled_interrupts = pending_interrupts & state.mideleg & -s_enabled;
 
-  if (state.dcsr.cause == 0 && enabled_interrupts) {
+  if (!state.debug_mode && enabled_interrupts) {
     // nonstandard interrupts have highest priority
     if (enabled_interrupts >> IRQ_M_EXT)
       enabled_interrupts = enabled_interrupts >> IRQ_M_EXT << IRQ_M_EXT;
@@ -331,6 +331,7 @@ void processor_t::set_privilege(reg_t prv)
 
 void processor_t::enter_debug_mode(uint8_t cause)
 {
+  state.debug_mode = true;
   state.dcsr.cause = cause;
   state.dcsr.prv = state.prv;
   set_privilege(PRV_M);
@@ -348,7 +349,7 @@ void processor_t::take_trap(trap_t& t, reg_t epc)
           t.get_tval());
   }
 
-  if (state.dcsr.cause) {
+  if (state.debug_mode) {
     if (t.cause() == CAUSE_BREAKPOINT) {
       state.pc = DEBUG_ROM_ENTRY;
     } else {
@@ -606,7 +607,7 @@ void processor_t::set_csr(int which, reg_t val)
     case CSR_TDATA1:
       {
         mcontrol_t *mc = &state.mcontrol[state.tselect];
-        if (mc->dmode && !state.dcsr.cause) {
+        if (mc->dmode && !state.debug_mode) {
           break;
         }
         mc->dmode = get_field(val, MCONTROL_DMODE(xlen));
@@ -629,7 +630,7 @@ void processor_t::set_csr(int which, reg_t val)
       }
       break;
     case CSR_TDATA2:
-      if (state.mcontrol[state.tselect].dmode && !state.dcsr.cause) {
+      if (state.mcontrol[state.tselect].dmode && !state.debug_mode) {
         break;
       }
       if (state.tselect < state.num_triggers) {

riscv/processor.h

@@ -232,12 +232,14 @@ struct state_t
   reg_t stvec;
   reg_t satp;
   reg_t scause;
+
   reg_t dpc;
   reg_t dscratch;
   dcsr_t dcsr;
   reg_t tselect;
   mcontrol_t mcontrol[num_triggers];
   reg_t tdata2[num_triggers];
+  bool debug_mode;
 
   static const int n_pmp = 16;
   uint8_t pmpcfg[n_pmp];
@@ -330,13 +332,13 @@ public:
   bool debug;
   // When true, take the slow simulation path.
   bool slow_path();
-  bool halted() { return state.dcsr.cause ? true : false; }
+  bool halted() { return state.debug_mode; }
   bool halt_request;
 
   // Return the index of a trigger that matched, or -1.
   inline int trigger_match(trigger_operation_t operation, reg_t address, reg_t data)
   {
-    if (state.dcsr.cause)
+    if (state.debug_mode)
       return -1;
 
     bool chain_ok = true;