Index: COFF/Config.h
===================================================================
--- COFF/Config.h
+++ COFF/Config.h
@@ -173,6 +173,9 @@
   // Used for /lldmap.
   std::string MapFile;
 
+  // Used for /functionpadmin.
+  uint32_t Padding = 0;
+
   uint64_t ImageBase = -1;
   uint64_t StackReserve = 1024 * 1024;
   uint64_t StackCommit = 4096;
Index: COFF/Driver.h
===================================================================
--- COFF/Driver.h
+++ COFF/Driver.h
@@ -159,6 +159,9 @@
 void parseSection(StringRef);
 void parseAligncomm(StringRef);
 
+// Parses a string in the form of "[:<integer>]"
+void parseFunctionpadmin(StringRef Arg, llvm::COFF::MachineTypes Machine);
+
 // Parses a string in the form of "EMBED[,=<integer>]|NO".
 void parseManifest(StringRef Arg);
 
Index: COFF/Driver.cpp
===================================================================
--- COFF/Driver.cpp
+++ COFF/Driver.cpp
@@ -1278,6 +1278,10 @@
   if (Config->Manifest == Configuration::Embed)
     addBuffer(createManifestRes(), false);
 
+  // Handle /functionpadmin
+  for (auto *Arg : Args.filtered(OPT_functionpadmin))
+    parseFunctionpadmin(Arg->getValue(), Config->Machine);
+
   // Read all input files given via the command line.
   run();
 
Index: COFF/DriverUtils.cpp
===================================================================
--- COFF/DriverUtils.cpp
+++ COFF/DriverUtils.cpp
@@ -250,6 +250,32 @@
   Config->AlignComm[Name] = std::max(Config->AlignComm[Name], 1 << V);
 }
 
+// Parses /functionpadmin option argument.
+void parseFunctionpadmin(StringRef Arg, llvm::COFF::MachineTypes Machine) {
+  StringRef Name, Padding;
+  std::tie(Name, Padding) = Arg.split(':');
+  if (!Padding.empty()) {
+    // Optional padding in bytes is given.
+    if (Padding.getAsInteger(0, Config->Padding)) {
+      error("/functionpadmin: invalid argument: " + Arg);
+      return;
+    }
+  } else {
+    // No optional argument given.
+    // Set default padding based on machine, similar to link.exe.
+    // There is no default padding for ARM platforms.
+    if (Machine == I386) {
+      Config->Padding = 5;
+    } else if (Machine == AMD64) {
+      Config->Padding = 6;
+    } else if (Machine == llvm::COFF::IMAGE_FILE_MACHINE_IA64) {
+      Config->Padding = 16;
+    } else {
+      error("/functionpadmin: invalid argument for this machine: " + Arg);
+    }
+  }
+}
+
 // Parses a string in the form of "EMBED[,=<integer>]|NO".
 // Results are directly written to Config.
 void parseManifest(StringRef Arg) {
Index: COFF/Options.td
===================================================================
--- COFF/Options.td
+++ COFF/Options.td
@@ -61,6 +61,7 @@
 def timestamp : P<"timestamp", "Specify the PE header timestamp">;
 def version : P<"version", "Specify a version number in the PE header">;
 def wholearchive_file : P<"wholearchive", "Include all object files from this archive">;
+def functionpadmin : Joined<["/", "-", "-?"], "functionpadmin">, HelpText<"Create hotpatchable image">;
 
 def disallowlib : Joined<["/", "-", "-?"], "disallowlib:">, Alias<nodefaultlib>;
 
@@ -166,7 +167,6 @@
   def _no : F<name#":no">;
 }
 
-def functionpadmin : F<"functionpadmin">;
 def ignoreidl : F<"ignoreidl">;
 def nologo : F<"nologo">;
 def throwingnew : F<"throwingnew">;
Index: COFF/Writer.cpp
===================================================================
--- COFF/Writer.cpp
+++ COFF/Writer.cpp
@@ -745,7 +745,23 @@
       addBaserels();
     uint64_t RawSize = 0, VirtualSize = 0;
     Sec->Header.VirtualAddress = RVA;
+
+    // If /FUNCTIONPADMIN is used, functions are padded in order to create a
+    // hotpatchable image.
+    const bool IsCodeSection =
+        (Sec->Header.Characteristics & IMAGE_SCN_CNT_CODE) &&
+        (Sec->Header.Characteristics & IMAGE_SCN_MEM_READ) &&
+        (Sec->Header.Characteristics & IMAGE_SCN_MEM_EXECUTE);
+    uint32_t Padding = IsCodeSection ? Config->Padding : 0;
+
     for (Chunk *C : Sec->getChunks()) {
+
+      // Apply padding to SectionChunks only.
+      if ((Padding != 0) && dyn_cast<SectionChunk>(C)) {
+        RawSize += Padding;
+        VirtualSize += Padding;
+      }
+
       VirtualSize = alignTo(VirtualSize, C->Alignment);
       C->setRVA(RVA + VirtualSize);
       C->OutputSectionOff = VirtualSize;