[wasm] Interpreter: Don't pause on invalid position

src/wasm/wasm-interpreter.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/wasm/wasm-interpreter.h"
 
 #include "src/utils.h"
 #include "src/wasm/decoder.h"
 #include "src/wasm/function-body-decoder.h"
 #include "src/wasm/wasm-external-refs.h"
@@ skipping 1165 matching lines @@
     stack_.resize(stack_.size() - pop_count);
   }
 
   void Execute(InterpreterCode* code, pc_t pc, int max) {
     Decoder decoder(code->start, code->end);
     pc_t limit = code->end - code->start;
     while (--max >= 0) {
 #define PAUSE_IF_BREAK_FLAG(flag) \
   if (V8_UNLIKELY(break_flags_ & WasmInterpreter::BreakFlag::flag)) max = 0;
 
-      if (pc >= limit) {
-        // Fell off end of code; do an implicit return.
-        TRACE("@%-3zu: ImplicitReturn\n", pc);
-        if (!DoReturn(&code, &pc, &limit, code->function->sig->return_count()))
-          return;
-        decoder.Reset(code->start, code->end);
-        PAUSE_IF_BREAK_FLAG(AfterReturn);
-        continue;
-      }
+      DCHECK_GT(limit, pc);
 
       const char* skip = "        ";
       int len = 1;
       byte opcode = code->start[pc];
       byte orig = opcode;
       if (V8_UNLIKELY(opcode == kInternalBreakpoint)) {
         orig = code->orig_start[pc];
         if (SkipBreakpoint(code, pc)) {
           // skip breakpoint by switching on original code.
           skip = "[skip]  ";
@@ skipping 423 matching lines @@
           FOREACH_OTHER_UNOP_NAN(EXECUTE_OTHER_UNOP_NAN)
 #undef EXECUTE_OTHER_UNOP_NAN
 
         default:
           V8_Fatal(__FILE__, __LINE__, "Unknown or unimplemented opcode #%d:%s",
                    code->start[pc], OpcodeName(code->start[pc]));
           UNREACHABLE();
       }
 
       pc += len;
+      if (pc == limit) {
+        // Fell off end of code; do an implicit return.
+        TRACE("@%-3zu: ImplicitReturn\n", pc);
+        if (!DoReturn(&code, &pc, &limit, code->function->sig->return_count()))
+          return;
+        decoder.Reset(code->start, code->end);
+        PAUSE_IF_BREAK_FLAG(AfterReturn);
+      }
     }
     // Set break_pc_, even though we might have stopped because max was reached.
     // We don't want to stop after executing zero instructions next time.
     break_pc_ = pc;
     state_ = WasmInterpreter::PAUSED;
     CommitPc(pc);
   }
 
   WasmVal Pop() {
     DCHECK_GT(stack_.size(), 0);
@@ skipping 274 matching lines @@
   return none;
 }
 
 void InterpretedFrame::SetLocalVal(int index, WasmVal val) { UNIMPLEMENTED(); }
 
 void InterpretedFrame::SetExprVal(int pc, WasmVal val) { UNIMPLEMENTED(); }
 
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8