Index: ELF/Config.h
===================================================================
--- ELF/Config.h
+++ ELF/Config.h
@@ -10,6 +10,7 @@
 #ifndef LLD_ELF_CONFIG_H
 #define LLD_ELF_CONFIG_H
 
+#include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/MapVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/ELF.h"
@@ -30,6 +31,11 @@
   ELF64BEKind
 };
 
+struct BuildIdBuilder {
+  void (*write)(uint8_t *Buf, std::vector<llvm::ArrayRef<uint8_t>> &Inputs);
+  size_t Size;
+};
+
 // This struct contains the global configuration for the linker.
 // Most fields are direct mapping from the command line options
 // and such fields have the same name as the corresponding options.
@@ -54,7 +60,6 @@
   bool AsNeeded = false;
   bool Bsymbolic;
   bool BsymbolicFunctions;
-  bool BuildId;
   bool Demangle = true;
   bool DiscardAll;
   bool DiscardLocals;
@@ -82,6 +87,7 @@
   bool ZNow;
   bool ZOrigin;
   bool ZRelro;
+  BuildIdBuilder *BuildId = nullptr;
   ELFKind EKind = ELFNoneKind;
   uint16_t EMachine = llvm::ELF::EM_NONE;
   uint64_t EntryAddr = -1;
Index: ELF/Driver.h
===================================================================
--- ELF/Driver.h
+++ ELF/Driver.h
@@ -57,6 +57,9 @@
 std::string searchLibrary(StringRef Path);
 std::string buildSysrootedPath(llvm::StringRef Dir, llvm::StringRef File);
 
+extern BuildIdBuilder BuildIdFnv1;
+extern BuildIdBuilder BuildIdMd5;
+
 } // namespace elf
 } // namespace lld
 
Index: ELF/Driver.cpp
===================================================================
--- ELF/Driver.cpp
+++ ELF/Driver.cpp
@@ -223,7 +223,6 @@
   Config->AllowMultipleDefinition = Args.hasArg(OPT_allow_multiple_definition);
   Config->Bsymbolic = Args.hasArg(OPT_Bsymbolic);
   Config->BsymbolicFunctions = Args.hasArg(OPT_Bsymbolic_functions);
-  Config->BuildId = Args.hasArg(OPT_build_id);
   Config->Demangle = !Args.hasArg(OPT_no_demangle);
   Config->DiscardAll = Args.hasArg(OPT_discard_all);
   Config->DiscardLocals = Args.hasArg(OPT_discard_locals);
@@ -277,6 +276,17 @@
       error("Unknown hash style: " + S);
   }
 
+  // Parse --build-id or --build-id=<style>.
+  if (Args.hasArg(OPT_build_id))
+    Config->BuildId = &BuildIdFnv1;
+  if (auto *Arg = Args.getLastArg(OPT_build_id_eq)) {
+    StringRef S = Arg->getValue();
+    if (S == "md5") {
+      Config->BuildId = &BuildIdMd5;
+    } else
+      error("unknown --build-id style: " + S);
+  }
+
   for (auto *Arg : Args.filtered(OPT_undefined))
     Config->Undefined.push_back(Arg->getValue());
 }
Index: ELF/DriverUtils.cpp
===================================================================
--- ELF/DriverUtils.cpp
+++ ELF/DriverUtils.cpp
@@ -19,6 +19,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/FileSystem.h"
+#include "llvm/Support/MD5.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/StringSaver.h"
 
@@ -26,6 +27,7 @@
 
 using namespace lld;
 using namespace lld::elf;
+using namespace llvm::support::endian;
 
 // Create OptTable
 
@@ -130,3 +132,27 @@
     sys::path::append(Path, Dir, File);
   return Path.str();
 }
+
+static void writeFnv1(uint8_t *Buf, std::vector<ArrayRef<uint8_t>> &V) {
+  // Compute the 64-bit FNV-1 hash for V and write it to Buf.
+  uint64_t Hash = 0xcbf29ce484222325;
+  for (ArrayRef<uint8_t> Arr : V) {
+    for (uint8_t B : Arr) {
+      Hash *= 0x100000001b3;
+      Hash ^= B;
+    }
+  }
+  write64le(Buf, Hash);
+}
+
+static void writeMd5(uint8_t *Buf, std::vector<ArrayRef<uint8_t>> &V) {
+  MD5 Hash;
+  for (ArrayRef<uint8_t> Arr : V)
+    Hash.update(Arr);
+  MD5::MD5Result Res;
+  Hash.final(Res);
+  memcpy(Buf, Res, 16);
+}
+
+BuildIdBuilder elf::BuildIdFnv1 = {writeFnv1, 8};
+BuildIdBuilder elf::BuildIdMd5 = {writeMd5, 16};
Index: ELF/Options.td
===================================================================
--- ELF/Options.td
+++ ELF/Options.td
@@ -15,6 +15,8 @@
 def build_id : Flag<["--", "-"], "build-id">,
   HelpText<"Generate build ID note">;
 
+def build_id_eq : Joined<["--", "-"], "build-id=">;
+
 def L : JoinedOrSeparate<["-"], "L">, MetaVarName<"<dir>">,
   HelpText<"Directory to search for libraries">;
 
Index: ELF/OutputSections.h
===================================================================
--- ELF/OutputSections.h
+++ ELF/OutputSections.h
@@ -520,7 +520,7 @@
   void writeBuildId();
 
 private:
-  uint64_t Hash = 0xcbf29ce484222325; // FNV1 hash basis
+  std::vector<ArrayRef<uint8_t>> Inputs;
   uint8_t *HashBuf;
 };
 
Index: ELF/OutputSections.cpp
===================================================================
--- ELF/OutputSections.cpp
+++ ELF/OutputSections.cpp
@@ -1532,31 +1532,25 @@
 template <class ELFT>
 BuildIdSection<ELFT>::BuildIdSection()
     : OutputSectionBase<ELFT>(".note.gnu.build-id", SHT_NOTE, SHF_ALLOC) {
-  // 16 bytes for the note section header and 8 bytes for FNV1 hash.
-  this->Header.sh_size = 24;
+  // 16 bytes for the note section header.
+  this->Header.sh_size = 16 + Config->BuildId->Size;
 }
 
 template <class ELFT> void BuildIdSection<ELFT>::writeTo(uint8_t *Buf) {
   const endianness E = ELFT::TargetEndianness;
-  write32<E>(Buf, 4);                   // Name size
-  write32<E>(Buf + 4, sizeof(Hash));    // Content size
-  write32<E>(Buf + 8, NT_GNU_BUILD_ID); // Type
-  memcpy(Buf + 12, "GNU", 4);           // Name string
+  write32<E>(Buf, 4);                         // Name size
+  write32<E>(Buf + 4, Config->BuildId->Size); // Content size
+  write32<E>(Buf + 8, NT_GNU_BUILD_ID);       // Type
+  memcpy(Buf + 12, "GNU", 4);                 // Name string
   HashBuf = Buf + 16;
 }
 
 template <class ELFT> void BuildIdSection<ELFT>::update(ArrayRef<uint8_t> Buf) {
-  // 64-bit FNV1 hash
-  const uint64_t Prime = 0x100000001b3;
-  for (uint8_t B : Buf) {
-    Hash *= Prime;
-    Hash ^= B;
-  }
+  Inputs.push_back(Buf);
 }
 
 template <class ELFT> void BuildIdSection<ELFT>::writeBuildId() {
-  const endianness E = ELFT::TargetEndianness;
-  write64<E>(HashBuf, Hash);
+  Config->BuildId->write(HashBuf, Inputs);
 }
 
 template <class ELFT>
Index: test/ELF/build-id.s
===================================================================
--- test/ELF/build-id.s
+++ test/ELF/build-id.s
@@ -2,15 +2,20 @@
 
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
 # RUN: ld.lld --build-id %t -o %t2
-# RUN: llvm-objdump -s %t2 | FileCheck -check-prefix=BUILDID %s
+# RUN: llvm-objdump -s %t2 | FileCheck -check-prefix=DEFAULT %s
+# RUN: ld.lld --build-id=md5 %t -o %t2
+# RUN: llvm-objdump -s %t2 | FileCheck -check-prefix=MD5 %s
 # RUN: ld.lld %t -o %t2
-# RUN: llvm-objdump -s %t2 | FileCheck -check-prefix=NO-BUILDID %s
+# RUN: llvm-objdump -s %t2 | FileCheck -check-prefix=NONE %s
 
 .globl _start;
 _start:
   nop
 
-# BUILDID:      Contents of section .note.gnu.build-id:
-# BUILDID-NEXT: 04000000 08000000 03000000 474e5500  ............GNU.
+# DEFAULT:      Contents of section .note.gnu.build-id:
+# DEFAULT-NEXT: 04000000 08000000 03000000 474e5500  ............GNU.
 
-# NO-BUILDID-NOT: Contents of section .note.gnu.build-id:
+# MD5:      Contents of section .note.gnu.build-id:
+# MD5-NEXT: 04000000 10000000 03000000 474e5500  ............GNU.
+
+# NONE-NOT: Contents of section .note.gnu.build-id: