[wasm] Enforce that function bodies end with the \"end\" opcode.

src/wasm/function-body-decoder.cc

 // Copyright 2015 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/signature.h"
 
 #include "src/bit-vector.h"
 #include "src/flags.h"
 #include "src/handles.h"
 #include "src/zone/zone-containers.h"
@@ skipping 21 matching lines @@
 #endif
 
 #define CHECK_PROTOTYPE_OPCODE(flag)                           \
   if (module_ != nullptr && module_->origin == kAsmJsOrigin) { \
     error("Opcode not supported for asmjs modules");           \
   }                                                            \
   if (!FLAG_##flag) {                                          \
     error("Invalid opcode (enable with --" #flag ")");         \
     break;                                                     \
   }
-// TODO(titzer): this is only for intermediate migration.
-#define IMPLICIT_FUNCTION_END 1
 
 // An SsaEnv environment carries the current local variable renaming
 // as well as the current effect and control dependency in the TF graph.
 // It maintains a control state that tracks whether the environment
 // is reachable, has reached a control end, or has been merged.
 struct SsaEnv {
   enum State { kControlEnd, kUnreachable, kReached, kMerged };
 
   State state;
   TFNode* control;
@@ skipping 432 matching lines @@
       return false;
     }
 
     DCHECK_EQ(0, local_types_->size());
     WasmDecoder::DecodeLocals(this, sig_, local_types_);
     InitSsaEnv();
     DecodeFunctionBody();
 
     if (failed()) return TraceFailed();
 
-#if IMPLICIT_FUNCTION_END
-    // With implicit end support (old style), the function block
-    // remains on the stack. Other control blocks are an error.
-    if (control_.size() > 1) {
-      error(pc_, control_.back().pc, "unterminated control structure");
+    if (!control_.empty()) {
+      // Generate a better error message whether the unterminated control
+      // structure is the function body block or an innner structure.
+      if (control_.size() > 1) {
+        error(pc_, control_.back().pc, "unterminated control structure");
+      } else {
+        error("function body must end with \"end\" opcode.");
+      }
       return TraceFailed();
     }
 
-    // Assume an implicit end to the function body block.
-    if (control_.size() == 1) {
-      Control* c = &control_.back();
-      if (ssa_env_->go()) {
-        FallThruTo(c);
-      }
-
-      if (c->end_env->go()) {
-        // Push the end values onto the stack.
-        stack_.resize(c->stack_depth);
-        if (c->merge.arity == 1) {
-          stack_.push_back(c->merge.vals.first);
-        } else {
-          for (unsigned i = 0; i < c->merge.arity; i++) {
-            stack_.push_back(c->merge.vals.array[i]);
-          }
-        }
-
-        TRACE("  @%-8d #xx:%-20s|", startrel(pc_), "ImplicitReturn");
-        SetEnv("function:end", c->end_env);
-        DoReturn();
-        TRACE("\n");
-      }
-    }
-#else
-    if (!control_.empty()) {
-      error(pc_, control_.back().pc, "unterminated control structure");
-      return TraceFailed();
-    }
-
     if (!last_end_found_) {
       error("function body must end with \"end\" opcode.");
       return false;
     }
-#endif
 
     if (FLAG_trace_wasm_decode_time) {
       double ms = decode_timer.Elapsed().InMillisecondsF();
       PrintF("wasm-decode %s (%0.3f ms)\n\n", ok() ? "ok" : "failed", ms);
     } else {
       TRACE("wasm-decode %s\n\n", ok() ? "ok" : "failed");
     }
 
     return true;
   }
@@ skipping 1507 matching lines @@
 BitVector* AnalyzeLoopAssignmentForTesting(Zone* zone, size_t num_locals,
                                            const byte* start, const byte* end) {
   Decoder decoder(start, end);
   return WasmDecoder::AnalyzeLoopAssignment(&decoder, start,
                                             static_cast<int>(num_locals), zone);
 }
 
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8