[PATCH] [lld][Core] Allow weak symbols in shared library when linking.

[Rui Ueyama]

Hi kledzik,

Currently lld always shows an error message when it finds an undefined
symbol in a shared library, even if the symbol is weak. That is, I think,
a wrong behavior.

Glibc has a weak symbol "_dl_starting_up". So the current lld always fails
to link an object when making an executable because of the error.

http://llvm-reviews.chandlerc.com/D694

Files:
  lib/Core/Resolver.cpp

Index: lib/Core/Resolver.cpp
===================================================================
--- lib/Core/Resolver.cpp
+++ lib/Core/Resolver.cpp
@@ -315,19 +315,21 @@
     bool foundUndefines = false;
     for (const UndefinedAtom *undefAtom : undefinedAtoms) {
       const File &f = undefAtom->file();
-      bool isAtomUndefined = false;
-      if (isa<SharedLibraryFile>(f)) {
-        if (!_targetInfo.allowShlibUndefines()) {
-          foundUndefines = true;
-          isAtomUndefined = true;
-        }
-      } else if (undefAtom->canBeNull() == UndefinedAtom::canBeNullNever) {
-        foundUndefines = true;
-        isAtomUndefined = true;
-      }
-      if (isAtomUndefined && _targetInfo.printRemainingUndefines()) {
-        llvm::errs() << "Undefined Symbol: " << undefAtom->file().path()
-                     << " : " << undefAtom->name() << "\n";
+
+      // Skip over a weak symbol.
+      if (undefAtom->canBeNull() != UndefinedAtom::canBeNullNever)
+        continue;
+
+      // If this is a library and undefined symbols are allowed on the
+      // target platform, skip over it.
+      if (isa<SharedLibraryFile>(f) && _targetInfo.allowShlibUndefines())
+        continue;
+
+      // Seems like this symbol is undefined. Warn that.
+      foundUndefines = true;
+      if (_targetInfo.printRemainingUndefines()) {
+          llvm::errs() << "Undefined Symbol: " << undefAtom->file().path()
+                       << " : " << undefAtom->name() << "\n";
       }
     }
     if (foundUndefines) {
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