fix use-after-free

Author: mingmingl-llvm

lld/ELF/InputFiles.cpp

@@ -1746,8 +1746,10 @@ createBitcodeSymbol(Symbol *&sym, const std::vector<bool> &keptComdats,
 
   // Symbols can be duplicated in bitcode files because of '#include' and
   // linkonce_odr. Use unique_saver to save symbol names for de-duplication.
-  if (!sym)
-    sym = symtab.insert(unique_saver().save(objSym.getName()));
+  if (!sym) {
+    objSym.Name = unique_saver().save(objSym.getName());
+    sym = symtab.insert(objSym.getName());
+  }
 
   int c = objSym.getComdatIndex();
   if (objSym.isUndefined() || (c != -1 && !keptComdats[c])) {
@@ -1797,18 +1799,18 @@ void BitcodeFile::parse() {
 void BitcodeFile::parseLazy() {
   numSymbols = obj->symbols().size();
   symbols = std::make_unique<Symbol *[]>(numSymbols);
-  for (auto [i, irSym] : llvm::enumerate(obj->symbols()))
+  for (auto [i, irSym] : llvm::enumerate(obj->symbols())) {
+    // Keep copies of per-module undefined symbols for LTO::GlobalResolutions
+    // usage.
+    irSym.Name = unique_saver().save(irSym.getName());
     if (!irSym.isUndefined()) {
       // Symbols can be duplicated in bitcode files because of '#include' and
       // linkonce_odr. Use unique_saver to save symbol names for de-duplication.
-      auto *sym = symtab.insert(unique_saver().save(irSym.getName()));
+      auto *sym = symtab.insert(irSym.getName());
       sym->resolve(LazySymbol{*this});
       symbols[i] = sym;
-    } else {
-      // Keep copies of per-module undefined symbols for LTO::GlobalResolutions
-      // usage.
-      unique_saver().save(irSym.getName());
     }
+  }
 }
 
 void BitcodeFile::postParse() {

llvm/include/llvm/LTO/LTO.h

@@ -138,7 +138,7 @@ class InputFile {
 
   /// The purpose of this class is to only expose the symbol information that an
   /// LTO client should need in order to do symbol resolution.
-  class Symbol : irsymtab::Symbol {
+  struct Symbol : irsymtab::Symbol {
     friend LTO;
 
   public:

llvm/include/llvm/Object/IRSymtab.h

@@ -169,7 +169,8 @@ Error build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,
 /// possibly a storage::Uncommon.
 struct Symbol {
   // Copied from storage::Symbol.
-  StringRef Name, IRName;
+  mutable StringRef Name;
+  StringRef IRName;
   int ComdatIndex;
   uint32_t Flags;