Index: llvm/include/llvm/MC/MCSectionXCOFF.h
===================================================================
--- llvm/include/llvm/MC/MCSectionXCOFF.h
+++ llvm/include/llvm/MC/MCSectionXCOFF.h
@@ -44,7 +44,7 @@
                  MCSymbolXCOFF *QualName, MCSymbol *Begin)
       : MCSection(SV_XCOFF, K, Begin), Name(Section), MappingClass(SMC),
         Type(ST), StorageClass(SC), QualName(QualName) {
-    assert((ST == XCOFF::XTY_SD || ST == XCOFF::XTY_CM) &&
+    assert((ST == XCOFF::XTY_SD || ST == XCOFF::XTY_CM || ST == XCOFF::XTY_ER) &&
            "Invalid or unhandled type for csect.");
     assert(QualName != nullptr && "QualName is needed.");
     QualName->setStorageClass(SC);
Index: llvm/include/llvm/MC/MCSymbolXCOFF.h
===================================================================
--- llvm/include/llvm/MC/MCSymbolXCOFF.h
+++ llvm/include/llvm/MC/MCSymbolXCOFF.h
@@ -48,6 +48,8 @@
     return ContainingCsect;
   }
 
+  bool hasContainingCsect() const { return ContainingCsect != nullptr; }
+
 private:
   Optional<XCOFF::StorageClass> StorageClass;
   MCSectionXCOFF *ContainingCsect = nullptr;
Index: llvm/lib/MC/XCOFFObjectWriter.cpp
===================================================================
--- llvm/lib/MC/XCOFFObjectWriter.cpp
+++ llvm/lib/MC/XCOFFObjectWriter.cpp
@@ -149,6 +149,7 @@
   // CsectGroups. These store the csects which make up different parts of
   // the sections. Should have one for each set of csects that get mapped into
   // the same section and get handled in a 'similar' way.
+  CsectGroup UndefinedCsects;
   CsectGroup ProgramCodeCsects;
   CsectGroup DataCsects;
   CsectGroup FuncDSCsects;
@@ -226,6 +227,8 @@
           CsectGroups{&BSSCsects}) {}
 
 void XCOFFObjectWriter::reset() {
+  UndefinedCsects.clear(); 
+
   // Reset any sections we have written to, and empty the section header table.
   for (auto *Sec : Sections)
     Sec->reset();
@@ -286,6 +289,8 @@
     const auto *MCSec = cast<const MCSectionXCOFF>(&S);
     assert(WrapperMap.find(MCSec) == WrapperMap.end() &&
            "Cannot add a csect twice.");
+    assert(XCOFF::XTY_ER != MCSec->getCSectType() &&
+           "An undefined csect should not get registered.");
 
     // If the name does not fit in the storage provided in the symbol table
     // entry, add it to the string table.
@@ -305,13 +310,19 @@
 
     // Map the symbol into its containing csect.
     const MCSectionXCOFF *ContainingCsect = XSym->getContainingCsect();
-    assert(WrapperMap.find(ContainingCsect) != WrapperMap.end() &&
-           "Expected containing csect to exist in map");
-
-    // If the symbol is the Csect itself, we don't need to put the symbol
-    // into Csect's Syms.
+   
+    // If the symbol is the csect itself, we don't need to put the symbol
+    // into csect's Syms.
     if (XSym == ContainingCsect->getQualNameSymbol())
       continue;
+    
+    if (XSym->isUndefined(false)) {
+      UndefinedCsects.emplace_back(ContainingCsect);
+      continue;
+    }
+
+    assert(WrapperMap.find(ContainingCsect) != WrapperMap.end() &&
+           "Expected containing csect to exist in map");
 
     // Lookup the containing csect and add the symbol to it.
     WrapperMap[ContainingCsect]->Syms.emplace_back(XSym);
@@ -525,6 +536,11 @@
 }
 
 void XCOFFObjectWriter::writeSymbolTable(const MCAsmLayout &Layout) {
+  for (const auto &Csect : UndefinedCsects) {
+    writeSymbolTableEntryForControlSection(
+        Csect, XCOFF::ReservedSectionNum::N_UNDEF, Csect.MCCsect->getStorageClass());
+  }
+
   for (const auto *Section : Sections) {
     // Nothing to write for this Section.
     if (Section->Index == Section::UninitializedIndex)
@@ -549,15 +565,25 @@
 }
 
 void XCOFFObjectWriter::assignAddressesAndIndices(const MCAsmLayout &Layout) {
+  // The first symbol table entry is for the file name. We are not emitting it
+  // yet, so start at index 0.
+  uint32_t SymbolTableIndex = 0;
+
+  // Calculate undefined symbol's indices.
+  for (auto &Csect : UndefinedCsects) {
+    Csect.Size = 0;
+    Csect.Address = 0;
+    Csect.SymbolTableIndex = SymbolTableIndex;
+    // 1 main and 1 auxiliary symbol table entry for each contained symbol.
+    SymbolTableIndex += 2;
+  }
+
   // The address corrresponds to the address of sections and symbols in the
   // object file. We place the shared address 0 immediately after the
   // section header table.
   uint32_t Address = 0;
   // Section indices are 1-based in XCOFF.
   int32_t SectionIndex = 1;
-  // The first symbol table entry is for the file name. We are not emitting it
-  // yet, so start at index 0.
-  uint32_t SymbolTableIndex = 0;
 
   for (auto *Section : Sections) {
     const bool IsEmpty =
Index: llvm/lib/Target/PowerPC/PPCISelLowering.cpp
===================================================================
--- llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -5317,8 +5317,20 @@
     // C-linkage name.
     GlobalAddressSDNode *G = cast<GlobalAddressSDNode>(Callee);
     auto &Context = DAG.getMachineFunction().getMMI().getContext();
-    MCSymbol *S = Context.getOrCreateSymbol(Twine(".") +
-                                            Twine(G->getGlobal()->getName()));
+    
+    MCSymbolXCOFF *S = cast<MCSymbolXCOFF>(Context.getOrCreateSymbol(
+        Twine(".") + Twine(G->getGlobal()->getName())));
+    
+    const GlobalValue *GV = G->getGlobal();
+    if (GV && GV->isDeclaration() && !S->hasContainingCsect()) {
+      // On AIX, undefined symbol need to associate with a MCSectionXCOFF to
+      // get the correct storage mapping class. In this case, XCOFF::XMC_PR.
+      MCSectionXCOFF *Sec =
+          Context.getXCOFFSection(S->getName(), XCOFF::XMC_PR, XCOFF::XTY_ER,
+                                  XCOFF::C_EXT, SectionKind::getMetadata());
+      S->setContainingCsect(Sec);
+    }
+
     Callee = DAG.getMCSymbol(S, PtrVT);
     // Replace the GlobalAddressSDNode Callee with the MCSymbolSDNode.
     Ops[1] = Callee;
Index: llvm/test/CodeGen/PowerPC/aix-undef-func-call.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/PowerPC/aix-undef-func-call.ll
@@ -0,0 +1,30 @@
+; RUN: llc -mtriple powerpc-ibm-aix-xcoff -filetype=obj -o %t.o < %s
+; RUN: llvm-readobj  --symbols %t.o | FileCheck %s
+
+define void @bar() {
+entry:
+  call void bitcast (void (...)* @foo to void ()*)()
+  ret void
+}
+
+declare void @foo(...)
+
+;CHECK: Symbol {
+;CHECK:   Name: .foo
+;CHECK-NEXT:   Value (RelocatableAddress): 0x0
+;CHECK-NEXT:   Section: N_UNDEF
+;CHECK-NEXT:   Type: 0x0
+;CHECK-NEXT:   StorageClass: C_EXT (0x2)
+;CHECK-NEXT:   NumberOfAuxEntries: 1
+;CHECK-NEXT:   CSECT Auxiliary Entry {
+;CHECK:          SectionLen: 0
+;CHECK-NEXT:     ParameterHashIndex: 0x0
+;CHECK-NEXT:     TypeChkSectNum: 0x0
+;CHECK-NEXT:     SymbolAlignmentLog2: 0
+;CHECK-NEXT:     SymbolType: XTY_ER (0x0)
+;CHECK-NEXT:     StorageMappingClass: XMC_PR (0x0)
+;CHECK-NEXT:     StabInfoIndex: 0x0
+;CHECK-NEXT:     StabSectNum: 0x0
+;CHECK-NEXT:   }
+;CHECK-NEXT: }
+