Index: ELF/MarkLive.cpp
===================================================================
--- ELF/MarkLive.cpp
+++ ELF/MarkLive.cpp
@@ -64,6 +64,12 @@
                          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 used.
+  B.Used = true;
+  if (auto *SS = dyn_cast<SharedSymbol>(&B))
+    if (!SS->isWeak())
+      SS->getFile<ELFT>()->IsNeeded = true;
+
   if (auto *D = dyn_cast<Defined>(&B)) {
     if (!D->Section)
       return;
Index: ELF/SymbolTable.cpp
===================================================================
--- ELF/SymbolTable.cpp
+++ ELF/SymbolTable.cpp
@@ -304,7 +304,8 @@
     if (!S->isDefined())
       S->Binding = Binding;
     if (auto *SS = dyn_cast<SharedSymbol>(S))
-      SS->getFile<ELFT>()->IsNeeded = true;
+      if (!Config->GcSections)
+        SS->getFile<ELFT>()->IsNeeded = true;
   }
   if (auto *L = dyn_cast<Lazy>(S)) {
     // An undefined weak will not fetch archive members. See comment on Lazy in
@@ -500,7 +501,7 @@
                                 Sym.st_value, Sym.st_size, Alignment, Verdef);
     if (!WasInserted) {
       S->Binding = Binding;
-      if (!S->isWeak())
+      if (!S->isWeak() && !Config->GcSections)
         File->IsNeeded = true;
     }
   }
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), Used(!Config->GcSections),
+        Type(Type), StOther(StOther), Name(Name) {}
 
   const unsigned SymbolKind : 8;
 
@@ -157,6 +157,9 @@
 
   unsigned IsPreemptible : 1;
 
+  // True if an undefined or shared symbol is used from a live section.
+  unsigned Used : 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
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.Used;
 }
 
 // Local symbols are not in the linker's symbol table. This function scans
Index: test/ELF/Inputs/gc-sections-shared2.s
===================================================================
--- /dev/null
+++ test/ELF/Inputs/gc-sections-shared2.s
@@ -0,0 +1,3 @@
+.global qux
+.type qux, @function
+qux:
Index: test/ELF/gc-collect-undefined.s
===================================================================
--- /dev/null
+++ test/ELF/gc-collect-undefined.s
@@ -0,0 +1,19 @@
+# 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-NOT: qux
+# 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
@@ -1,14 +1,18 @@
 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/shared.s -o %t2.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/gc-sections-shared.s -o %t3.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/gc-sections-shared2.s -o %t4.o
 # RUN: ld.lld -shared %t2.o -o %t2.so
 # RUN: ld.lld -shared %t3.o -o %t3.so
+# RUN: ld.lld -shared %t4.o -o %t4.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 %t3.so
+# RUN: ld.lld --gc-sections --export-dynamic-symbol foo -o %t %t.o --as-needed %t2.so %t3.so %t4.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
+# It would also be OK to keep bar2 and the need for %t2.so
+# At the same time, weak symbols should not cause adding DT_NEEDED;
+# this case is checked with symbol qux and %t4.so.
 
 # CHECK:      DynamicSymbols [
 # CHECK-NEXT:   Symbol {
@@ -21,16 +25,16 @@
 # 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
@@ -39,13 +43,13 @@
 # CHECK-NEXT:     Section: .text
 # CHECK-NEXT:   }
 # CHECK-NEXT:   Symbol {
-# CHECK-NEXT:     Name: foo
+# CHECK-NEXT:     Name: qux
 # CHECK-NEXT:     Value:
 # CHECK-NEXT:     Size:
-# CHECK-NEXT:     Binding: Global
+# CHECK-NEXT:     Binding: Weak
 # CHECK-NEXT:     Type:
 # CHECK-NEXT:     Other:
-# CHECK-NEXT:     Section: .text
+# CHECK-NEXT:     Section: Undefined
 # CHECK-NEXT:   }
 # CHECK-NEXT:   Symbol {
 # CHECK-NEXT:     Name: baz
@@ -59,7 +63,6 @@
 # CHECK-NEXT: ]
 
 # CHECK-NOT: NEEDED
-# CHECK:     NEEDED Shared library: [{{.*}}2.so]
 # CHECK:     NEEDED Shared library: [{{.*}}3.so]
 # CHECK-NOT: NEEDED
 
@@ -75,8 +78,10 @@
 
 .section .text._start, "ax"
 .globl _start
+.weak qux
 _start:
 call baz
+call qux
 ret
 
 .section .text.unused, "ax"