make nemu behave like nop on gem5ops

src/isa/riscv64/include/isa-all-instr.h

@@ -116,7 +116,7 @@
   f(fmadds) f(fmsubs) f(fnmsubs) f(fnmadds) f(fmaddd) f(fmsubd) f(fnmsubd) f(fnmaddd)
 
 #define INSTR_NULLARY(f) \
-  f(inv) f(rt_inv) f(nemu_trap) \
+  f(inv) f(rt_inv) f(nemu_trap) f(gem5_trap)\
   f(fence_i) f(fence) \
   SYS_INSTR_NULLARY(f) \
   f(p_ret)

src/isa/riscv64/instr/decode.c

@@ -54,6 +54,7 @@ def_THelper(main) {
   def_INSTR_TAB  ("??????? ????? ????? ??? ????? 11010 ??",         nemu_trap);
   def_INSTR_IDTAB("??????? ????? ????? ??? ????? 11011 ??", J     , jal_dispatch);
   def_INSTR_IDTAB("??????? ????? ????? ??? ????? 11100 ??", csr   , system);
+  def_INSTR_TAB  ("??????? ????? ????? ??? ????? 11110 ??",         gem5_trap);
   return table_inv(s);
 };
 

src/isa/riscv64/instr/special.h

@@ -16,3 +16,7 @@ def_EHelper(nemu_trap) {
   rtl_hostcall(s, HOSTCALL_EXIT, NULL, &cpu.gpr[10]._64, NULL, 0); // gpr[10] is $a0
   longjmp_exec(NEMU_EXEC_END);
 }
+
+def_EHelper(gem5_trap) {
+  //do nothing
+}
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