Bug 1501703: Move the custom section read before finishing a wasm module's metadata; r=luke

--HG--
extra : rebase_source : 0384cec0612899e5778876aa0264871dfacffc96
extra : amend_source : 56ba7c68842e503aae67525efa030c13e631188c

js/src/wasm/WasmGenerator.cpp

@@ -978,7 +978,7 @@ ModuleGenerator::finishCodeTier()
     return js::MakeUnique<CodeTier>(std::move(metadataTier_), std::move(segment));
 }
 
-bool
+SharedMetadata
 ModuleGenerator::finishMetadata(const Bytes& bytecode)
 {
     // Finish initialization of Metadata, which is only needed for constructing
@@ -1005,14 +1005,14 @@ ModuleGenerator::finishMetadata(const Bytes& bytecode)
 
         const size_t numFuncTypes = env_->funcTypes.length();
         if (!metadata_->debugFuncArgTypes.resize(numFuncTypes)) {
-            return false;
+            return nullptr;
         }
         if (!metadata_->debugFuncReturnTypes.resize(numFuncTypes)) {
-            return false;
+            return nullptr;
         }
         for (size_t i = 0; i < numFuncTypes; i++) {
             if (!metadata_->debugFuncArgTypes[i].appendAll(env_->funcTypes[i]->args())) {
-                return false;
+                return nullptr;
             }
             metadata_->debugFuncReturnTypes[i] = env_->funcTypes[i]->ret();
         }
@@ -1026,7 +1026,12 @@ ModuleGenerator::finishMetadata(const Bytes& bytecode)
         memcpy(metadata_->debugHash, hash, sizeof(ModuleHash));
     }
 
-    return true;
+    MOZ_ASSERT_IF(env_->nameCustomSectionIndex, !!metadata_->namePayload);
+
+    // Metadata shouldn't be mutably modified after finishMetadata().
+    SharedMetadata metadata = metadata_;
+    metadata_ = nullptr;
+    return metadata;
 }
 
 SharedModule
@@ -1046,23 +1051,6 @@ ModuleGenerator::finishModule(const ShareableBytes& bytecode,
         return nullptr;
     }
 
-    if (!finishMetadata(bytecode.bytes)) {
-        return nullptr;
-    }
-
-    StructTypeVector structTypes;
-    for (TypeDef& td : env_->types) {
-        if (td.isStructType() && !structTypes.append(std::move(td.structType()))) {
-            return nullptr;
-        }
-    }
-
-    MutableCode code = js_new<Code>(std::move(codeTier), *metadata_, std::move(jumpTables),
-                                    std::move(structTypes));
-    if (!code || !code->initialize(*linkData_)) {
-        return nullptr;
-    }
-
     // Copy over data from the Bytecode, which is going away at the end of
     // compilation.
 
@@ -1105,6 +1093,24 @@ ModuleGenerator::finishModule(const ShareableBytes& bytecode,
         metadata_->namePayload = customSections[*env_->nameCustomSectionIndex].payload;
     }
 
+    SharedMetadata metadata = finishMetadata(bytecode.bytes);
+    if (!metadata) {
+        return nullptr;
+    }
+
+    StructTypeVector structTypes;
+    for (TypeDef& td : env_->types) {
+        if (td.isStructType() && !structTypes.append(std::move(td.structType()))) {
+            return nullptr;
+        }
+    }
+
+    MutableCode code = js_new<Code>(std::move(codeTier), *metadata, std::move(jumpTables),
+                                    std::move(structTypes));
+    if (!code || !code->initialize(*linkData_)) {
+        return nullptr;
+    }
+
     // See Module debugCodeClaimed_ comments for why we need to make a separate
     // debug copy.
 

js/src/wasm/WasmGenerator.h

@@ -202,7 +202,7 @@ class MOZ_STACK_CLASS ModuleGenerator
     bool finishCodegen();
     bool finishMetadataTier();
     UniqueCodeTier finishCodeTier();
-    bool finishMetadata(const Bytes& bytecode);
+    SharedMetadata finishMetadata(const Bytes& bytecode);
 
     bool isAsmJS() const { return env_->isAsmJS(); }
     Tier tier() const { return env_->tier(); }