Implement dcsr.v and make DRET use it

Resolves #1365

riscv/csrs.cc

@@ -13,6 +13,8 @@
 #include "trap.h"
 // For require():
 #include "insn_macros.h"
+// For CSR_DCSR_V:
+#include "debug_defines.h"
 
 // STATE macro used by require_privilege() macro:
 #undef STATE
@@ -1234,6 +1236,7 @@ dcsr_csr_t::dcsr_csr_t(processor_t* const proc, const reg_t addr):
   ebreaks(false),
   ebreaku(false),
   halt(false),
+  v(false),
   cause(0) {
 }
 
@@ -1255,6 +1258,7 @@ reg_t dcsr_csr_t::read() const noexcept {
   result = set_field(result, DCSR_CAUSE, cause);
   result = set_field(result, DCSR_STEP, step);
   result = set_field(result, DCSR_PRV, prv);
+  result = set_field(result, CSR_DCSR_V, v);
   return result;
 }
 
@@ -1267,12 +1271,14 @@ bool dcsr_csr_t::unlogged_write(const reg_t val) noexcept {
   ebreaks = get_field(val, DCSR_EBREAKS);
   ebreaku = get_field(val, DCSR_EBREAKU);
   halt = get_field(val, DCSR_HALT);
+  v = proc->extension_enabled('H') ? get_field(val, CSR_DCSR_V) : false;
   return true;
 }
 
-void dcsr_csr_t::write_cause_and_prv(uint8_t cause, reg_t prv) noexcept {
+void dcsr_csr_t::write_cause_and_prv(uint8_t cause, reg_t prv, bool v) noexcept {
   this->cause = cause;
   this->prv = prv;
+  this->v = v;
   log_write();
 }
 

riscv/csrs.h

@@ -656,7 +656,7 @@ class dcsr_csr_t: public csr_t {
   dcsr_csr_t(processor_t* const proc, const reg_t addr);
   virtual void verify_permissions(insn_t insn, bool write) const override;
   virtual reg_t read() const noexcept override;
-  void write_cause_and_prv(uint8_t cause, reg_t prv) noexcept;
+  void write_cause_and_prv(uint8_t cause, reg_t prv, bool v) noexcept;
  protected:
   virtual bool unlogged_write(const reg_t val) noexcept override;
  public:
@@ -667,6 +667,7 @@ class dcsr_csr_t: public csr_t {
   bool ebreaks;
   bool ebreaku;
   bool halt;
+  bool v;
   uint8_t cause;
 };
 

riscv/insns/dret.h

@@ -1,6 +1,7 @@
 require(STATE.debug_mode);
 set_pc_and_serialize(STATE.dpc->read());
 p->set_privilege(STATE.dcsr->prv);
+p->set_virt(STATE.dcsr->v);
 if (STATE.prv < PRV_M)
   STATE.mstatus->write(STATE.mstatus->read() & ~MSTATUS_MPRV);
 

riscv/processor.cc

@@ -763,7 +763,7 @@ void processor_t::set_virt(bool virt)
 void processor_t::enter_debug_mode(uint8_t cause)
 {
   state.debug_mode = true;
-  state.dcsr->write_cause_and_prv(cause, state.prv);
+  state.dcsr->write_cause_and_prv(cause, state.prv, state.v);
   set_privilege(PRV_M);
   state.dpc->write(state.pc);
   state.pc = DEBUG_ROM_ENTRY;