diff --git a/llvm/include/llvm/BinaryFormat/Wasm.h b/llvm/include/llvm/BinaryFormat/Wasm.h
--- a/llvm/include/llvm/BinaryFormat/Wasm.h
+++ b/llvm/include/llvm/BinaryFormat/Wasm.h
@@ -243,7 +243,7 @@
   WASM_OPCODE_F64_CONST = 0x44,
 };
 
-enum : unsigned {
+enum : uint8_t {
   WASM_LIMITS_FLAG_HAS_MAX = 0x1,
   WASM_LIMITS_FLAG_IS_SHARED = 0x2,
 };
diff --git a/llvm/include/llvm/MC/MCSymbolWasm.h b/llvm/include/llvm/MC/MCSymbolWasm.h
--- a/llvm/include/llvm/MC/MCSymbolWasm.h
+++ b/llvm/include/llvm/MC/MCSymbolWasm.h
@@ -23,6 +23,7 @@
   wasm::WasmSignature *Signature = nullptr;
   Optional<wasm::WasmGlobalType> GlobalType;
   Optional<wasm::WasmEventType> EventType;
+  uint8_t MemFlags = 0;
 
   /// An expression describing how to calculate the size of a symbol. If a
   /// symbol has no size this field will be NULL.
@@ -78,6 +79,9 @@
   }
   void setImportName(StringRef Name) { ImportName = Name; }
 
+  uint8_t getMemFlags() const { return MemFlags; }
+  void setMemFlags(uint8_t F) { MemFlags = F; }
+
   const wasm::WasmSignature *getSignature() const { return Signature; }
   void setSignature(wasm::WasmSignature *Sig) { Signature = Sig; }
 
diff --git a/llvm/lib/MC/WasmObjectWriter.cpp b/llvm/lib/MC/WasmObjectWriter.cpp
--- a/llvm/lib/MC/WasmObjectWriter.cpp
+++ b/llvm/lib/MC/WasmObjectWriter.cpp
@@ -750,8 +750,10 @@
       W.OS << char(Import.Global.Mutable ? 1 : 0);
       break;
     case wasm::WASM_EXTERNAL_MEMORY:
-      encodeULEB128(0, W.OS);        // flags
-      encodeULEB128(NumPages, W.OS); // initial
+      encodeULEB128(Import.Memory.Flags, W.OS); // flags
+      encodeULEB128(NumPages, W.OS);            // initial
+      if (Import.Memory.Flags & wasm::WASM_LIMITS_FLAG_HAS_MAX)
+        encodeULEB128(NumPages, W.OS);          // max
       break;
     case wasm::WASM_EXTERNAL_TABLE:
       W.OS << char(Import.Table.ElemType);
@@ -1170,6 +1172,7 @@
   MemImport.Module = MemorySym->getImportModule();
   MemImport.Field = MemorySym->getImportName();
   MemImport.Kind = wasm::WASM_EXTERNAL_MEMORY;
+  MemImport.Memory.Flags = MemorySym->getMemFlags();
   Imports.push_back(MemImport);
 
   // For now, always emit the table section, since indirect calls are not
diff --git a/llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp b/llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp
--- a/llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp
+++ b/llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp
@@ -651,6 +651,11 @@
       return expect(AsmToken::EndOfStatement, "EOL");
     }
 
+    if (DirectiveID.getString() == ".shared_memory") {
+      TOut.emitSharedMemory();
+      return expect(AsmToken::EndOfStatement, "EOL");
+    }
+
     return true; // We didn't process this directive.
   }
 
diff --git a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.h b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.h
--- a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.h
+++ b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.h
@@ -49,6 +49,9 @@
   virtual void emitImportName(const MCSymbolWasm *Sym,
                               StringRef ImportName) = 0;
 
+  /// .shared_memory
+  virtual void emitSharedMemory() = 0;
+
 protected:
   void emitValueType(wasm::ValType Type);
 };
@@ -71,6 +74,7 @@
   void emitEventType(const MCSymbolWasm *Sym) override;
   void emitImportModule(const MCSymbolWasm *Sym, StringRef ImportModule) override;
   void emitImportName(const MCSymbolWasm *Sym, StringRef ImportName) override;
+  void emitSharedMemory() override;
 };
 
 /// This part is for Wasm object output
@@ -88,6 +92,7 @@
                         StringRef ImportModule) override {}
   void emitImportName(const MCSymbolWasm *Sym,
                       StringRef ImportName) override {}
+  void emitSharedMemory() override;
 };
 
 /// This part is for null output
@@ -104,6 +109,7 @@
   void emitEventType(const MCSymbolWasm *) override {}
   void emitImportModule(const MCSymbolWasm *, StringRef) override {}
   void emitImportName(const MCSymbolWasm *, StringRef) override {}
+  void emitSharedMemory() override {}
 };
 
 } // end namespace llvm
diff --git a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.cpp b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.cpp
--- a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.cpp
+++ b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.cpp
@@ -123,6 +123,10 @@
                            << ImportName << '\n';
 }
 
+void WebAssemblyTargetAsmStreamer::emitSharedMemory() {
+  OS << "\t.shared_memory\n";
+}
+
 void WebAssemblyTargetAsmStreamer::emitIndIdx(const MCExpr *Value) {
   OS << "\t.indidx  \t" << *Value << '\n';
 }
@@ -150,3 +154,11 @@
 void WebAssemblyTargetWasmStreamer::emitIndIdx(const MCExpr *Value) {
   llvm_unreachable(".indidx encoding not yet implemented");
 }
+
+void WebAssemblyTargetWasmStreamer::emitSharedMemory() {
+  // __linear_memory is always included in the object, this just makes it shared
+  auto Sym = cast<MCSymbolWasm>(
+      getStreamer().getContext().getOrCreateSymbol("__linear_memory"));
+  Sym->setMemFlags(wasm::WASM_LIMITS_FLAG_HAS_MAX |
+                   wasm::WASM_LIMITS_FLAG_IS_SHARED);
+}
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.h b/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.h
--- a/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.h
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.h
@@ -57,6 +57,7 @@
   // AsmPrinter Implementation.
   //===------------------------------------------------------------------===//
 
+  void EmitStartOfAsmFile(Module &M) override;
   void EmitEndOfAsmFile(Module &M) override;
   void EmitProducerInfo(Module &M);
   void EmitJumpTableInfo() override;
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
--- a/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
@@ -81,6 +81,12 @@
 // WebAssemblyAsmPrinter Implementation.
 //===----------------------------------------------------------------------===//
 
+void WebAssemblyAsmPrinter::EmitStartOfAsmFile(Module &M) {
+  if (TM.Options.ThreadModel != ThreadModel::Single) {
+    getTargetStreamer()->emitSharedMemory();
+  }
+}
+
 void WebAssemblyAsmPrinter::EmitEndOfAsmFile(Module &M) {
   for (auto &It : OutContext.getSymbols()) {
     // Emit a .globaltype and .eventtype declaration.
diff --git a/llvm/test/MC/WebAssembly/assembler-binary.ll b/llvm/test/MC/WebAssembly/assembler-binary.ll
--- a/llvm/test/MC/WebAssembly/assembler-binary.ll
+++ b/llvm/test/MC/WebAssembly/assembler-binary.ll
@@ -21,14 +21,17 @@
 ; Checking assembly is not the point of this test, but if something breaks
 ; it is easier to spot it here than in the yaml output.
 
-; ASM:     	.text
-; ASM:      	.file	"assembler-binary.ll"
-; ASM:      	.globl	foo
-; ASM:      foo:
-; ASM-NEXT: 	.functype	foo (i32) -> ()
-; ASM-NEXT: 	call	bar@FUNCTION
-; ASM-NEXT: 	end_function
-; ASM:       	.functype	bar () -> ()
+; ASM:          .text
+; ASM:          .shared
+; ASM-NEXT:     .file "assembler-binary.ll"
+; ASM-DAG:     .section .text.foo,"",@
+; ASM-DAG:     .globl foo
+
+; ASM:     foo:
+; ASM-NEXT:     .functype foo (i32) -> ()
+; ASM-NEXT:     call bar@FUNCTION
+; ASM-NEXT:     end_function
+; ASM:         .functype bar () -> ()
 
 
 ; CHECK:      --- !WASM
@@ -50,7 +53,9 @@
 ; CHECK-NEXT:         Field:           __linear_memory
 ; CHECK-NEXT:         Kind:            MEMORY
 ; CHECK-NEXT:         Memory:
+; CHECK-NEXT:           Flags:           [ HAS_MAX, IS_SHARED ]
 ; CHECK-NEXT:           Initial:         0x00000000
+; CHECK-NEXT:           Maximum:         0x00000000
 ; CHECK-NEXT:       - Module:          env
 ; CHECK-NEXT:         Field:           __indirect_function_table
 ; CHECK-NEXT:         Kind:            TABLE
diff --git a/llvm/test/MC/WebAssembly/custom-sections.ll b/llvm/test/MC/WebAssembly/custom-sections.ll
--- a/llvm/test/MC/WebAssembly/custom-sections.ll
+++ b/llvm/test/MC/WebAssembly/custom-sections.ll
@@ -1,4 +1,4 @@
-; RUN: llc -filetype=obj %s -o - | llvm-readobj -s | FileCheck %s
+; RUN: llc -filetype=obj -thread-model=single %s -o - | llvm-readobj -s | FileCheck %s
 
 ; Test the mechanism for defining user custom sections.
 
diff --git a/llvm/test/MC/WebAssembly/event-section.ll b/llvm/test/MC/WebAssembly/event-section.ll
--- a/llvm/test/MC/WebAssembly/event-section.ll
+++ b/llvm/test/MC/WebAssembly/event-section.ll
@@ -1,5 +1,5 @@
-; RUN: llc -filetype=obj -exception-model=wasm -mattr=+exception-handling %s -o - | obj2yaml | FileCheck %s
-; RUN: llc -filetype=obj -exception-model=wasm -mattr=+exception-handling %s -o - | llvm-readobj -s | FileCheck -check-prefix=SEC %s
+; RUN: llc -filetype=obj -thread-model=single -exception-model=wasm -mattr=+exception-handling %s -o - | obj2yaml | FileCheck %s
+; RUN: llc -filetype=obj -thread-model=single -exception-model=wasm -mattr=+exception-handling %s -o - | llvm-readobj -s | FileCheck -check-prefix=SEC %s
 
 target triple = "wasm32-unknown-unknown"
 
diff --git a/llvm/test/ObjectYAML/wasm/memory_section.yaml b/llvm/test/ObjectYAML/wasm/memory_section.yaml
--- a/llvm/test/ObjectYAML/wasm/memory_section.yaml
+++ b/llvm/test/ObjectYAML/wasm/memory_section.yaml
@@ -9,6 +9,10 @@
         Initial:         0x00000002
         Maximum:         0x000000FF
       - Initial:         0x00000003
+      - Flags:           [ HAS_MAX, IS_SHARED ]
+        Initial:         0x00000042
+        Maximum:         0x00000042
+
 ...
 # CHECK: --- !WASM
 # CHECK: FileHeader:
@@ -20,4 +24,7 @@
 # CHECK:         Initial:          0x00000002
 # CHECK:         Maximum:          0x000000FF
 # CHECK:       - Initial:          0x00000003
+# CHECK:       - Flags:            [ HAS_MAX, IS_SHARED ]
+# CHECK:         Initial:          0x00000042
+# CHECK:         Maximum:          0x00000042
 # CHECK: ...