2 files changed, 18 insertions, 2 deletions
diff --git a/lld/lib/Core/Resolver.cpp b/lld/lib/Core/Resolver.cpp
index d56f7d1067f..716f0d48d53 100644
--- a/lld/lib/Core/Resolver.cpp
+++ b/lld/lib/Core/Resolver.cpp
@@ -198,7 +198,7 @@ void Resolver::resolveUndefines() {
     undefineGenCount = _symbolTable.size();
     std::vector<const UndefinedAtom *> undefines;
     _symbolTable.undefines(undefines);
-    for ( const Atom *undefAtom : undefines ) {
+    for (const UndefinedAtom *undefAtom : undefines) {
       StringRef undefName = undefAtom->name();
       // load for previous undefine may also have loaded this undefine
       if (!_symbolTable.isDefined(undefName)) {
@@ -208,6 +208,13 @@ void Resolver::resolveUndefines() {
                                     false,  // dataSymbolOnly
                                     *this);
       }
+      // If the undefined symbol has an alternative name, try to resolve the
+      // symbol with the name to give it a second chance. This feature is used
+      // for COFF "weak external" symbol.
+      if (const UndefinedAtom *fallbackUndefAtom = undefAtom->fallback()) {
+        _symbolTable.addReplacement(undefAtom, fallbackUndefAtom);
+        _symbolTable.add(*fallbackUndefAtom);
+      }
     }
     // search libraries for overrides of common symbols
     if (searchArchives || searchSharedLibs) {
diff --git a/lld/lib/Core/SymbolTable.cpp b/lld/lib/Core/SymbolTable.cpp
index 3b43c2effa8..8fee4bb41e3 100644
--- a/lld/lib/Core/SymbolTable.cpp
+++ b/lld/lib/Core/SymbolTable.cpp
@@ -311,6 +311,11 @@ bool SymbolTable::isDefined(StringRef sym) {
   return true;
 }
 
+void SymbolTable::addReplacement(const Atom *replaced,
+                                 const Atom *replacement) {
+  _replacedAtoms[replaced] = replacement;
+}
+
 const Atom *SymbolTable::replacement(const Atom *atom) {
   AtomToAtom::iterator pos = _replacedAtoms.find(atom);
   if (pos == _replacedAtoms.end())
@@ -328,8 +333,12 @@ void SymbolTable::undefines(std::vector<const UndefinedAtom *> &undefs) {
        end = _nameTable.end(); it != end; ++it) {
     const Atom *atom = it->second;
     assert(atom != nullptr);
-    if (const auto undef = dyn_cast<const UndefinedAtom>(atom))
+    if (const auto undef = dyn_cast<const UndefinedAtom>(atom)) {
+      AtomToAtom::iterator pos = _replacedAtoms.find(undef);
+      if (pos != _replacedAtoms.end())
+        continue;
       undefs.push_back(undef);
+    }
   }
 }