Index: llvm/include/llvm/MC/MCWinEH.h
===================================================================
--- llvm/include/llvm/MC/MCWinEH.h
+++ llvm/include/llvm/MC/MCWinEH.h
@@ -53,6 +53,15 @@
             const FrameInfo *ChainedParent)
       : Begin(BeginFuncEHLabel), Function(Function),
         ChainedParent(ChainedParent) {}
+
+  bool empty() const {
+    if (!Instructions.empty())
+      return false;
+    for (const auto &E : EpilogMap)
+      if (!E.second.empty())
+        return false;
+    return true;
+  }
 };
 
 class UnwindEmitter {
Index: llvm/lib/MC/MCWin64EH.cpp
===================================================================
--- llvm/lib/MC/MCWin64EH.cpp
+++ llvm/lib/MC/MCWin64EH.cpp
@@ -576,7 +576,13 @@
   if (CodeWordsMod)
     CodeWords++;
   uint32_t EpilogCount = info->EpilogMap.size();
-  bool ExtensionWord = EpilogCount > 31 || TotalCodeBytes > 124;
+  // If we need to signal a larger EpilogCount or TotalCodeBytes, we need to
+  // use the extension word, and leave those fields as zero in row1.
+  // If both EpilogCount and CodeWords actually are zero though (e.g. due to
+  // missing/incomplete .seh directives in assembly), we still need to include
+  // the extension word, as that is how the reader will interpret it.
+  bool ExtensionWord = EpilogCount > 31 || TotalCodeBytes > 124 ||
+                       (EpilogCount == 0 && CodeWords == 0);
   if (!ExtensionWord) {
     row1 |= (EpilogCount & 0x1F) << 22;
     row1 |= (CodeWords & 0x1F) << 27;
@@ -657,16 +663,25 @@
 void llvm::Win64EH::ARM64UnwindEmitter::Emit(MCStreamer &Streamer) const {
   // Emit the unwind info structs first.
   for (const auto &CFI : Streamer.getWinFrameInfos()) {
+    WinEH::FrameInfo *Info = CFI.get();
+    if (Info->empty())
+      continue;
     MCSection *XData = Streamer.getAssociatedXDataSection(CFI->TextSection);
     Streamer.SwitchSection(XData);
-    ARM64EmitUnwindInfo(Streamer, CFI.get());
+    ARM64EmitUnwindInfo(Streamer, Info);
   }
 
   // Now emit RUNTIME_FUNCTION entries.
   for (const auto &CFI : Streamer.getWinFrameInfos()) {
+    WinEH::FrameInfo *Info = CFI.get();
+    // ARM64EmitUnwindInfo above clears the info struct, so we can't check
+    // empty here. But if a Symbol is set, we should create the corresponding
+    // pdata entry.
+    if (!Info->Symbol)
+      continue;
     MCSection *PData = Streamer.getAssociatedPDataSection(CFI->TextSection);
     Streamer.SwitchSection(PData);
-    ARM64EmitRuntimeFunction(Streamer, CFI.get());
+    ARM64EmitRuntimeFunction(Streamer, Info);
   }
 }
 
Index: llvm/test/MC/AArch64/seh.s
===================================================================
--- llvm/test/MC/AArch64/seh.s
+++ llvm/test/MC/AArch64/seh.s
@@ -1,6 +1,8 @@
 // This test checks that the SEH directives don't cause the assembler to fail.
+// Checking that llvm-readobj doesn't bail out on the unwind data, but not
+// really checking the contents yet.
 
-// RUN: llvm-mc -triple aarch64-pc-win32 -filetype=obj %s | llvm-readobj -S -r - | FileCheck %s
+// RUN: llvm-mc -triple aarch64-pc-win32 -filetype=obj %s | llvm-readobj -S -r -u - | FileCheck %s
 
 // CHECK:      Sections [
 // CHECK:        Section {
@@ -15,8 +17,8 @@
 // CHECK-NEXT:   }
 // CHECK:        Section {
 // CHECK:          Name: .xdata
-// CHECK:          RawDataSize: 20
-// CHECK:          RelocationCount: 1
+// CHECK:          RawDataSize: 32
+// CHECK:          RelocationCount: 2
 // CHECK:          Characteristics [
 // CHECK-NEXT:       ALIGN_4BYTES
 // CHECK-NEXT:       CNT_INITIALIZED_DATA
@@ -37,11 +39,12 @@
 // CHECK-NEXT: Relocations [
 // CHECK-NEXT:   Section (4) .xdata {
 // CHECK-NEXT:     0x8 IMAGE_REL_ARM64_ADDR32NB __C_specific_handler
+// CHECK-NEXT:     0x18 IMAGE_REL_ARM64_ADDR32NB __C_specific_handler
 // CHECK-NEXT:   }
 // CHECK-NEXT:   Section (5) .pdata {
 // CHECK-NEXT:     0x0 IMAGE_REL_ARM64_ADDR32NB func
 // CHECK-NEXT:     0x4 IMAGE_REL_ARM64_ADDR32NB .xdata
-// CHECK-NEXT:     0x8 IMAGE_REL_ARM64_ADDR32NB smallFunc
+// CHECK-NEXT:     0x8 IMAGE_REL_ARM64_ADDR32NB handlerFunc
 // CHECK-NEXT:     0xC IMAGE_REL_ARM64_ADDR32NB .xdata
 // CHECK-NEXT:   }
 // CHECK-NEXT: ]
@@ -67,7 +70,8 @@
     ret
     .seh_endproc
 
-// Test emission of small functions.
+    // Function with no .seh directives; no pdata/xdata entries are
+    // generated.
     .globl smallFunc
     .def smallFunc
     .scl 2
@@ -77,3 +81,19 @@
 smallFunc:
     ret
     .seh_endproc
+
+    // Function with no .seh directives, but with .seh_handlerdata, which
+    // forces generating the xdata/pdata entries.
+    .globl handlerFunc
+    .def handlerFunc
+    .scl 2
+    .type 32
+    .endef
+    .seh_proc handlerFunc
+handlerFunc:
+    ret
+    .seh_handler __C_specific_handler, @except
+    .seh_handlerdata
+    .long 0
+    .text
+    .seh_endproc