Index: ELF/MarkLive.cpp
===================================================================
--- ELF/MarkLive.cpp
+++ ELF/MarkLive.cpp
@@ -64,6 +64,9 @@
                          std::function<void(InputSectionBase *, uint64_t)> Fn) {
   Symbol &B = Sec.getFile<ELFT>()->getRelocTargetSym(Rel);
 
+  // If a symbol is referenced in a live section, it is alive.
+  B.ForceLive = true;
+
   if (auto *Sym = dyn_cast<SharedSymbol>(&B))
     if (!Sym->isWeak())
       cast<SharedFile<ELFT>>(Sym->File)->IsNeeded = true;
@@ -216,10 +219,6 @@
   };
 
   auto MarkSymbol = [&](Symbol *Sym) {
-    if (auto *S = dyn_cast_or_null<SharedSymbol>(Sym))
-      if (!S->isWeak())
-        cast<SharedFile<ELFT>>(S->File)->IsNeeded = true;
-
     if (auto *D = dyn_cast_or_null<Defined>(Sym))
       if (auto *IS = cast_or_null<InputSectionBase>(D->Section))
         Enqueue(IS, D->Value);
Index: ELF/Symbols.h
===================================================================
--- ELF/Symbols.h
+++ ELF/Symbols.h
@@ -134,8 +134,8 @@
          uint8_t Type)
       : Binding(Binding), SymbolKind(K), NeedsPltAddr(false),
         IsInGlobalMipsGot(false), Is32BitMipsGot(false), IsInIplt(false),
-        IsInIgot(false), IsPreemptible(false), Type(Type), StOther(StOther),
-        Name(Name) {}
+        IsInIgot(false), IsPreemptible(false), ForceLive(false), Type(Type),
+        StOther(StOther), Name(Name) {}
 
   const unsigned SymbolKind : 8;
 
@@ -157,6 +157,9 @@
 
   unsigned IsPreemptible : 1;
 
+  // True if GC marked this symbol alive because it is used in a live section.
+  unsigned ForceLive : 1;
+
   // The following fields have the same meaning as the ELF symbol attributes.
   uint8_t Type;    // symbol type
   uint8_t StOther; // st_other field value
@@ -363,6 +366,7 @@
   S->CanInline = Sym.CanInline;
   S->Traced = Sym.Traced;
   S->InVersionScript = Sym.InVersionScript;
+  S->ForceLive = Sym.ForceLive;
 
   // Print out a log message if --trace-symbol was specified.
   // This is for debugging.
Index: ELF/Writer.cpp
===================================================================
--- ELF/Writer.cpp
+++ ELF/Writer.cpp
@@ -441,8 +441,9 @@
     if (auto *S = dyn_cast<MergeInputSection>(Sec))
       if (!S->getSectionPiece(D->Value)->Live)
         return false;
+    return true;
   }
-  return true;
+  return B.ForceLive || !Config->GcSections;
 }
 
 // Local symbols are not in the linker's symbol table. This function scans
Index: test/ELF/gc-collect-undefined.s
===================================================================
--- /dev/null
+++ test/ELF/gc-collect-undefined.s
@@ -0,0 +1,18 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: ld.lld %t -o %tout --gc-sections -shared
+# RUN: llvm-nm -D %tout | FileCheck %s
+
+# CHECK: bar
+# CHECK-NOT: qux
+
+	.global foo,bar,qux
+	.local baz
+
+	.section .data.foo,"aw",%progbits
+foo:
+	.dc.a	bar
+
+	.section .bata.baz,"aw",%progbits
+baz:
+	.dc.a	qux
Index: test/ELF/gc-sections-shared.s
===================================================================
--- test/ELF/gc-sections-shared.s
+++ test/ELF/gc-sections-shared.s
@@ -1,12 +1,15 @@
 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/shared.s -o %t2.o
 # RUN: ld.lld -shared %t2.o -o %t2.so
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/shared3.s -o %t3.o
+# RUN: ld.lld -shared %t3.o -o %t3.so
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
-# RUN: ld.lld --gc-sections --export-dynamic-symbol foo -o %t %t.o --as-needed %t2.so
+# RUN: ld.lld --gc-sections --export-dynamic-symbol foo -o %t %t.o --as-needed %t2.so %t3.so
 # RUN: llvm-readobj --dynamic-table --dyn-symbols %t | FileCheck %s
 
 # This test the property that we have a needed line for every undefined.
-# It would also be OK to drop bar2 and the need for the .so
+# '%t2.so' is dropped because 'bar2' is eliminated, whereas
+# '%t3.so' is preserved because 'baz' is used.
 
 # CHECK:      DynamicSymbols [
 # CHECK-NEXT:   Symbol {
@@ -19,16 +22,16 @@
 # CHECK-NEXT:     Section: Undefined (0x0)
 # CHECK-NEXT:   }
 # CHECK-NEXT:   Symbol {
-# CHECK-NEXT:     Name: bar2
+# CHECK-NEXT:     Name: bar
 # CHECK-NEXT:     Value:
 # CHECK-NEXT:     Size:
 # CHECK-NEXT:     Binding: Global
 # CHECK-NEXT:     Type:
 # CHECK-NEXT:     Other:
-# CHECK-NEXT:     Section: Undefined
+# CHECK-NEXT:     Section: .text
 # CHECK-NEXT:   }
 # CHECK-NEXT:   Symbol {
-# CHECK-NEXT:     Name: bar
+# CHECK-NEXT:     Name: foo
 # CHECK-NEXT:     Value:
 # CHECK-NEXT:     Size:
 # CHECK-NEXT:     Binding: Global
@@ -37,22 +40,24 @@
 # CHECK-NEXT:     Section: .text
 # CHECK-NEXT:   }
 # CHECK-NEXT:   Symbol {
-# CHECK-NEXT:     Name: foo
+# CHECK-NEXT:     Name: baz
 # CHECK-NEXT:     Value:
 # CHECK-NEXT:     Size:
 # CHECK-NEXT:     Binding: Global
 # CHECK-NEXT:     Type:
 # CHECK-NEXT:     Other:
-# CHECK-NEXT:     Section: .text
+# CHECK-NEXT:     Section: Undefined
 # CHECK-NEXT:   }
 # CHECK-NEXT: ]
 
-# CHECK: NEEDED Shared library: [{{.*}}.so]
+# CHECK-NOT: NEEDED Shared library: [{{.*}}2.so]
+# CHECK:     NEEDED Shared library: [{{.*}}3.so]
 
 .section .text.foo, "ax"
 .globl foo
 foo:
 call bar
+call baz
 
 .section .text.bar, "ax"
 .globl bar