[WebAssembly][MC] Fix leak of std::string members in MCSymbolWasm

Summary: Fixes: https://bugs.llvm.org/show_bug.cgi?id=45452

Subscribers: dschuff, jgravelle-google, hiraditya, aheejin, sunfish, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D77627

include/llvm/MC/MCSymbolWasm.h

@@ -19,13 +19,15 @@ class MCSymbolWasm : public MCSymbol {
   bool IsHidden = false;
   bool IsComdat = false;
   mutable bool IsUsedInGOT = false;
-  Optional<std::string> ImportModule;
-  Optional<std::string> ImportName;
-  Optional<std::string> ExportName;
-  wasm::WasmSignature *Signature = nullptr;
   Optional<wasm::WasmGlobalType> GlobalType;
   Optional<wasm::WasmEventType> EventType;
 
+  // Non-owning pointers since MCSymbol must be trivially destructible.
+  std::string *ImportModule = nullptr;
+  std::string *ImportName = nullptr;
+  std::string *ExportName = nullptr;
+  wasm::WasmSignature *Signature = nullptr;
+
   /// An expression describing how to calculate the size of a symbol. If a
   /// symbol has no size this field will be NULL.
   const MCExpr *SymbolSize = nullptr;
@@ -69,37 +71,32 @@ public:
   bool isComdat() const { return IsComdat; }
   void setComdat(bool isComdat) { IsComdat = isComdat; }
 
-  bool hasImportModule() const { return ImportModule.hasValue(); }
+  bool hasImportModule() const { return ImportModule != nullptr; }
   const StringRef getImportModule() const {
-      if (ImportModule.hasValue()) {
-          return ImportModule.getValue();
-      }
-      // Use a default module name of "env" for now, for compatibility with
-      // existing tools.
-      // TODO(sbc): Find a way to specify a default value in the object format
-      // without picking a hardcoded value like this.
-      return "env";
-  }
-  void setImportModule(StringRef Name) {
-    ImportModule = std::string(std::string(Name));
+    if (ImportModule)
+      return StringRef(*ImportModule);
+    // Use a default module name of "env" for now, for compatibility with
+    // existing tools.
+    // TODO(sbc): Find a way to specify a default value in the object format
+    // without picking a hardcoded value like this.
+    return "env";
   }
+  void setImportModule(std::string *Name) { ImportModule = Name; }
 
-  bool hasImportName() const { return ImportName.hasValue(); }
+  bool hasImportName() const { return ImportName != nullptr; }
   const StringRef getImportName() const {
-      if (ImportName.hasValue()) {
-          return ImportName.getValue();
-      }
-      return getName();
-  }
-  void setImportName(StringRef Name) {
-    ImportName = std::string(std::string(Name));
+    if (ImportName)
+      return StringRef(*ImportName);
+    return getName();
   }
+  void setImportName(std::string *Name) { ImportName = Name; }
 
-  bool hasExportName() const { return ExportName.hasValue(); }
-  const StringRef getExportName() const { return ExportName.getValue(); }
-  void setExportName(StringRef Name) {
-    ExportName = std::string(std::string(Name));
+  bool hasExportName() const { return ExportName != nullptr; }
+  const StringRef getExportName() const {
+    assert(ExportName);
+    return StringRef(*ExportName);
   }
+  void setExportName(std::string *Name) { ExportName = Name; }
 
   void setUsedInGOT() const { IsUsedInGOT = true; }
   bool isUsedInGOT() const { return IsUsedInGOT; }

lib/MC/MCContext.cpp

@@ -158,6 +158,16 @@ MCSymbol *MCContext::getOrCreateLSDASymbol(StringRef FuncName) {
 
 MCSymbol *MCContext::createSymbolImpl(const StringMapEntry<bool> *Name,
                                       bool IsTemporary) {
+  static_assert(std::is_trivially_destructible<MCSymbolCOFF>(),
+                "MCSymbol classes must be trivially destructible");
+  static_assert(std::is_trivially_destructible<MCSymbolELF>(),
+                "MCSymbol classes must be trivially destructible");
+  static_assert(std::is_trivially_destructible<MCSymbolMachO>(),
+                "MCSymbol classes must be trivially destructible");
+  static_assert(std::is_trivially_destructible<MCSymbolWasm>(),
+                "MCSymbol classes must be trivially destructible");
+  static_assert(std::is_trivially_destructible<MCSymbolXCOFF>(),
+                "MCSymbol classes must be trivially destructible");
   if (MOFI) {
     switch (MOFI->getObjectFileType()) {
     case MCObjectFileInfo::IsCOFF:

lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp

@@ -164,6 +164,7 @@ class WebAssemblyAsmParser final : public MCTargetAsmParser {
 
   // Much like WebAssemblyAsmPrinter in the backend, we have to own these.
   std::vector<std::unique_ptr<wasm::WasmSignature>> Signatures;
+  std::vector<std::unique_ptr<std::string>> Names;
 
   // Order of labels, directives and instructions in a .s file have no
   // syntactical enforcement. This class is a callback from the actual parser,
@@ -232,6 +233,12 @@ public:
     Signatures.push_back(std::move(Sig));
   }
 
+  std::string *storeName(StringRef Name) {
+    std::unique_ptr<std::string> N = std::make_unique<std::string>(Name);
+    Names.push_back(std::move(N));
+    return Names.back().get();
+  }
+
   std::pair<StringRef, StringRef> nestingString(NestingType NT) {
     switch (NT) {
     case Function:
@@ -725,7 +732,7 @@ public:
         return true;
       auto ExportName = expectIdent();
       auto WasmSym = cast<MCSymbolWasm>(Ctx.getOrCreateSymbol(SymName));
-      WasmSym->setExportName(ExportName);
+      WasmSym->setExportName(storeName(ExportName));
       TOut.emitExportName(WasmSym, ExportName);
     }
 
@@ -737,7 +744,7 @@ public:
         return true;
       auto ImportModule = expectIdent();
       auto WasmSym = cast<MCSymbolWasm>(Ctx.getOrCreateSymbol(SymName));
-      WasmSym->setImportModule(ImportModule);
+      WasmSym->setImportModule(storeName(ImportModule));
       TOut.emitImportModule(WasmSym, ImportModule);
     }
 
@@ -749,7 +756,7 @@ public:
         return true;
       auto ImportName = expectIdent();
       auto WasmSym = cast<MCSymbolWasm>(Ctx.getOrCreateSymbol(SymName));
-      WasmSym->setImportName(ImportName);
+      WasmSym->setImportName(storeName(ImportName));
       TOut.emitImportName(WasmSym, ImportName);
     }
 

lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp

@@ -122,14 +122,14 @@ void WebAssemblyAsmPrinter::emitEndOfAsmFile(Module &M) {
           F.hasFnAttribute("wasm-import-module")) {
         StringRef Name =
             F.getFnAttribute("wasm-import-module").getValueAsString();
-        Sym->setImportModule(Name);
+        Sym->setImportModule(storeName(Name));
         getTargetStreamer()->emitImportModule(Sym, Name);
       }
       if (TM.getTargetTriple().isOSBinFormatWasm() &&
           F.hasFnAttribute("wasm-import-name")) {
         StringRef Name =
             F.getFnAttribute("wasm-import-name").getValueAsString();
-        Sym->setImportName(Name);
+        Sym->setImportName(storeName(Name));
         getTargetStreamer()->emitImportName(Sym, Name);
       }
     }
@@ -137,7 +137,7 @@ void WebAssemblyAsmPrinter::emitEndOfAsmFile(Module &M) {
     if (F.hasFnAttribute("wasm-export-name")) {
       auto *Sym = cast<MCSymbolWasm>(getSymbol(&F));
       StringRef Name = F.getFnAttribute("wasm-export-name").getValueAsString();
-      Sym->setExportName(Name);
+      Sym->setExportName(storeName(Name));
       getTargetStreamer()->emitExportName(Sym, Name);
     }
   }

lib/Target/WebAssembly/WebAssemblyAsmPrinter.h

@@ -26,6 +26,13 @@ class LLVM_LIBRARY_VISIBILITY WebAssemblyAsmPrinter final : public AsmPrinter {
   WebAssemblyFunctionInfo *MFI;
   // TODO: Do the uniquing of Signatures here instead of ObjectFileWriter?
   std::vector<std::unique_ptr<wasm::WasmSignature>> Signatures;
+  std::vector<std::unique_ptr<std::string>> Names;
+
+  std::string *storeName(StringRef Name) {
+    std::unique_ptr<std::string> N = std::make_unique<std::string>(Name);
+    Names.push_back(std::move(N));
+    return Names.back().get();
+  }
 
 public:
   explicit WebAssemblyAsmPrinter(TargetMachine &TM,