added OP_CALL_FALLBACK

src/jit/backend/x64/x64_backend.cc

@@ -1652,6 +1652,15 @@ EMITTER(CALL_EXTERNAL) {
   e.call(e.rax);
 }
 
+EMITTER(CALL_FALLBACK) {
+  void *fallback = (void *)instr->arg[0]->i64;
+  uint32_t addr = instr->arg[1]->i32;
+
+  e.mov(arg0, addr);
+  e.mov(e.rax, reinterpret_cast<uint64_t>(fallback));
+  e.call(e.rax);
+}
+
 struct jit_backend *x64_backend_create(const struct jit_guest *guest) {
   struct x64_backend *backend = reinterpret_cast<struct x64_backend *>(
       calloc(1, sizeof(struct x64_backend)));

src/jit/ir/ir.c

@@ -737,3 +737,9 @@ void ir_call_external_2(struct ir *ir, struct ir_value *addr,
   ir_set_arg0(ir, instr, addr);
   ir_set_arg1(ir, instr, arg0);
 }
+
+void ir_call_fallback(struct ir *ir, void *fallback, uint32_t raw_instr) {
+  struct ir_instr *instr = ir_append_instr(ir, OP_CALL_FALLBACK, VALUE_V);
+  ir_set_arg0(ir, instr, ir_alloc_i64(ir, (uint64_t)fallback));
+  ir_set_arg1(ir, instr, ir_alloc_i32(ir, raw_instr));
+}

src/jit/ir/ir.h

@@ -325,5 +325,6 @@ void ir_branch_cond(struct ir *ir, struct ir_value *cond,
 void ir_call_external_1(struct ir *ir, struct ir_value *addr);
 void ir_call_external_2(struct ir *ir, struct ir_value *addr,
                         struct ir_value *arg0);
+void ir_call_fallback(struct ir *ir, void *fallback, uint32_t raw_instr);
 
 #endif

src/jit/ir/ir_ops.inc

@@ -48,3 +48,4 @@ IR_OP(LSHD)
 IR_OP(BRANCH)
 IR_OP(BRANCH_COND)
 IR_OP(CALL_EXTERNAL)
+IR_OP(CALL_FALLBACK)

src/jit/jit.c

@@ -287,9 +287,9 @@ struct jit *jit_create(struct jit_guest *guest, struct jit_frontend *frontend,
 
   // initialize all entries in block jit to reference the default block
   jit->default_code = default_code;
-  jit->code = malloc(jit->guest.max_blocks * sizeof(struct jit_block));
+  jit->code = malloc(jit->guest.block_max * sizeof(struct jit_block));
 
-  for (int i = 0; i < jit->guest.max_blocks; i++) {
+  for (int i = 0; i < jit->guest.block_max; i++) {
     jit->code[i] = default_code;
   }
 

src/jit/jit.h

@@ -25,7 +25,7 @@ struct jit_guest {
   // used by the jit to map guest addresses to block offsets
   uint32_t block_mask;
   uint32_t block_shift;
-  int max_blocks;
+  int block_max;
 
   // used by the backend
   void *ctx_base;