Only implement one solution for native triggers.

When S-mode is present, use option 1 (disable triggers in M-mode unless
MIE is set) from the Debug Spec. When S-mode is not present, use option
2 (implement mte and mpte bits in tcontrol).

See discussion in riscv-software-src#1777.

riscv/csr_init.cc

@@ -205,13 +205,14 @@ void state_t::csr_init(processor_t* const proc, reg_t max_isa)
     add_csr(CSR_TDATA2, tdata2 = std::make_shared<tdata2_csr_t>(proc, CSR_TDATA2));
     add_csr(CSR_TDATA3, std::make_shared<tdata3_csr_t>(proc, CSR_TDATA3));
     add_csr(CSR_TINFO, std::make_shared<tinfo_csr_t>(proc, CSR_TINFO));
-    add_csr(CSR_TCONTROL, tcontrol = std::make_shared<masked_csr_t>(proc, CSR_TCONTROL, CSR_TCONTROL_MPTE | CSR_TCONTROL_MTE, 0));
+    if (!proc->extension_enabled_const('S')) {
+      add_csr(CSR_TCONTROL, tcontrol = std::make_shared<masked_csr_t>(proc, CSR_TCONTROL, CSR_TCONTROL_MPTE | CSR_TCONTROL_MTE, 0));
+    }
   } else {
     add_csr(CSR_TDATA1, std::make_shared<const_csr_t>(proc, CSR_TDATA1, 0));
     add_csr(CSR_TDATA2, tdata2 = std::make_shared<const_csr_t>(proc, CSR_TDATA2, 0));
     add_csr(CSR_TDATA3, std::make_shared<const_csr_t>(proc, CSR_TDATA3, 0));
     add_csr(CSR_TINFO, std::make_shared<const_csr_t>(proc, CSR_TINFO, 0));
-    add_csr(CSR_TCONTROL, tcontrol = std::make_shared<const_csr_t>(proc, CSR_TCONTROL, 0));
   }
   unsigned scontext_length = (xlen == 32 ? 16 : 32); // debug spec suggests 16-bit for RV32 and 32-bit for RV64
   add_supervisor_csr(CSR_SCONTEXT, scontext = std::make_shared<masked_csr_t>(proc, CSR_SCONTEXT, (reg_t(1) << scontext_length) - 1, 0));

riscv/triggers.cc

@@ -66,7 +66,12 @@ bool trigger_t::common_match(processor_t * const proc, bool use_prev_prv) const
   auto state = proc->get_state();
   auto prv = use_prev_prv ? state->prev_prv : state->prv;
   auto v = use_prev_prv ? state->prev_v : state->v;
-  auto m_enabled = get_action() != 0 || (tcontrol_value(state) & CSR_TCONTROL_MTE);
+  bool m_enabled = get_action() != 0;
+  if (!m_enabled && proc->extension_enabled('S')) {
+    m_enabled |= tcontrol_value(state) & CSR_TCONTROL_MTE;
+  } else {
+    m_enabled |= state->mstatus->read() & MSTATUS_MIE;
+  }
   return (prv < PRV_M || m_enabled) && mode_match(prv, v) && textra_match(proc);
 }
 
@@ -121,14 +126,25 @@ bool trigger_t::allow_action(processor_t * const proc) const
 {
   const state_t *state = proc->get_state();
   if (get_action() == ACTION_DEBUG_EXCEPTION) {
-    const bool mstatus_mie = state->mstatus->read() & MSTATUS_MIE;
-    const bool sstatus_sie = state->sstatus->read() & MSTATUS_SIE;
-    const bool vsstatus_sie = state->vsstatus->read() & MSTATUS_SIE;
-    const bool medeleg_breakpoint = (state->medeleg->read() >> CAUSE_BREAKPOINT) & 1;
-    const bool hedeleg_breakpoint = (state->hedeleg->read() >> CAUSE_BREAKPOINT) & 1;
-    return (state->prv != PRV_M || mstatus_mie) &&
-           (state->prv != PRV_S || state->v || !medeleg_breakpoint || sstatus_sie) &&
-           (state->prv != PRV_S || !state->v || !medeleg_breakpoint || !hedeleg_breakpoint || vsstatus_sie);
+    if (proc->extension_enabled('S')) {
+      // The hardware prevents triggers with action=0 from matching or firing
+      // while in M-mode and while MIE in mstatus is 0. If medeleg [3]=1 then it
+      // prevents triggers with action=0 from matching or firing while in S-mode
+      // and while SIE in sstatus is 0. If medeleg [3]=1 and hedeleg [3]=1 then
+      // it prevents triggers with action=0 from matching or firing while in
+      // VS-mode and while SIE in vstatus is 0.
+      const bool mstatus_mie = state->mstatus->read() & MSTATUS_MIE;
+      const bool sstatus_sie = state->sstatus->read() & MSTATUS_SIE;
+      const bool vsstatus_sie = state->vsstatus->read() & MSTATUS_SIE;
+      const bool medeleg_breakpoint = (state->medeleg->read() >> CAUSE_BREAKPOINT) & 1;
+      const bool hedeleg_breakpoint = (state->hedeleg->read() >> CAUSE_BREAKPOINT) & 1;
+      return (state->prv != PRV_M || mstatus_mie) &&
+            (state->prv != PRV_S || state->v || !medeleg_breakpoint || sstatus_sie) &&
+            (state->prv != PRV_S || !state->v || !medeleg_breakpoint || !hedeleg_breakpoint || vsstatus_sie);
+    } else {
+      // mte and mpte in tcontrol is implemented. medeleg [3] is hard-wired to 0.
+      return (state->prv != PRV_M) || (tcontrol_value(state) & CSR_TCONTROL_MTE);
+    }
   }
   return true;
 }