Don't use reexecution as the means to implement trigger-after

The scheme was based on the notion that memory accesses are idempotent
up until the point the trigger would've been hit, which isn't true in
the case of side-effecting loads and data-value triggers.

Instead, check the trigger on the next instruction fetch.  To keep the
perf overhead minimal, perform this check on the I$ refill path, and
ensure that path is taken by flushing the I$.

1 files changed, 4 insertions, 1 deletions

diff --git a/riscv/mmu.cc b/riscv/mmu.cc
index b8690ec..fdad05f 100644
--- a/riscv/mmu.cc
+++ b/riscv/mmu.cc
@@ -165,8 +165,11 @@ void mmu_t::check_triggers(triggers::operation_t operation, reg_t address, bool
       throw triggers::matched_t(operation, address, data, action);
 
     case triggers::MATCH_FIRE_AFTER:
+      // We want to take this exception on the next instruction.  We check
+      // whether to do so in the I$ refill path, so flush the I$.
+      flush_icache();
       matched_trigger = new triggers::matched_t(operation, address, data, action);
-      throw *matched_trigger;
+      return;
   }
 }