Index: ELF/Config.h
===================================================================
--- ELF/Config.h
+++ ELF/Config.h
@@ -89,6 +89,7 @@
   bool VersionScript = false;
   bool WarnCommon;
   bool ZCombreloc;
+  bool ZDefs;
   bool ZExecStack;
   bool ZNodelete;
   bool ZNow;
Index: ELF/Driver.cpp
===================================================================
--- ELF/Driver.cpp
+++ ELF/Driver.cpp
@@ -353,6 +353,7 @@
     error("number of threads must be > 0");
 
   Config->ZCombreloc = !hasZOption(Args, "nocombreloc");
+  Config->ZDefs = hasZOption(Args, "defs");
   Config->ZExecStack = hasZOption(Args, "execstack");
   Config->ZNodelete = hasZOption(Args, "nodelete");
   Config->ZNow = hasZOption(Args, "now");
Index: ELF/Writer.cpp
===================================================================
--- ELF/Writer.cpp
+++ ELF/Writer.cpp
@@ -793,7 +793,7 @@
   if (!Config->NoUndefined) {
     if (Config->Relocatable)
       return;
-    if (Config->Shared)
+    if (Config->Shared && !Config->ZDefs)
       if (Sym->symbol()->Visibility == STV_DEFAULT)
         return;
   }
Index: test/ELF/zdefs.s
===================================================================
--- test/ELF/zdefs.s
+++ test/ELF/zdefs.s
@@ -0,0 +1,7 @@
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+# RUN: ld.lld -shared %t.o -o %t1.so
+
+# RUN: not ld.lld -z defs -shared %t.o -o %t1.so 2>&1 | FileCheck -check-prefix=ERR %s
+# ERR: undefined symbol: foo
+
+callq foo@PLT