Index: lld/trunk/test/wasm/shared-memory-no-atomics.yaml
===================================================================
--- lld/trunk/test/wasm/shared-memory-no-atomics.yaml
+++ lld/trunk/test/wasm/shared-memory-no-atomics.yaml
@@ -0,0 +1,60 @@
+# RUN: yaml2obj %s -o %t1.o
+
+# RUN: wasm-ld --no-entry %t1.o -o - | obj2yaml | FileCheck %s --check-prefix NO-SHARED
+
+# RUN: not wasm-ld --no-entry --shared-memory --max-memory=131072 %t1.o -o - 2>&1 | FileCheck %s --check-prefix SHARED
+
+--- !WASM
+FileHeader:
+  Version:         0x00000001
+Sections:
+  - Type:            IMPORT
+    Imports:
+      - Module:          env
+        Field:           __linear_memory
+        Kind:            MEMORY
+        Memory:
+          Initial:         0x00000001
+      - Module:          env
+        Field:           __indirect_function_table
+        Kind:            TABLE
+        Table:
+          ElemType:        FUNCREF
+          Limits:
+            Initial:         0x00000000
+  - Type:            DATA
+    Segments:
+      - SectionOffset:   6
+        InitFlags:       0
+        Offset:
+          Opcode:          I32_CONST
+          Value:           0
+        Content:         68656C6C6F0A00
+  - Type:            CUSTOM
+    Name:            linking
+    Version:         2
+    SymbolTable:
+      - Index:           0
+        Kind:            DATA
+        Name:            hello_str
+        Flags:           [  ]
+        Segment:         0
+        Size:            7
+    SegmentInfo:
+      - Index:           0
+        Name:            .rodata.hello_str
+        Alignment:       0
+        Flags:           [  ]
+  - Type:            CUSTOM
+    Name:            target_features
+    Features:
+      - Prefix:        DISALLOWED
+        Name:          "atomics"
+...
+
+# NO-SHARED:      - Type:            MEMORY
+# NO-SHARED-NEXT:   Memories:
+# NO-SHARED-NEXT:     - Initial:         0x00000002
+# NO-SHARED-NOT:        Maximum:
+
+# SHARED: 'atomics' feature is disallowed, so --shared-memory must not be used{{$}}
Index: lld/trunk/test/wasm/shared-memory.yaml
===================================================================
--- lld/trunk/test/wasm/shared-memory.yaml
+++ lld/trunk/test/wasm/shared-memory.yaml
@@ -0,0 +1,75 @@
+# RUN: yaml2obj %s -o %t1.o
+
+# RUN: not wasm-ld --no-entry --shared-memory %t1.o -o - 2>&1 | FileCheck %s --check-prefix SHARED-NO-MAX
+
+# RUN: not wasm-ld --no-entry --shared-memory --max-memory=100000 %t1.o -o - 2>&1 | FileCheck %s --check-prefix SHARED-UNALIGNED
+
+# RUN: wasm-ld --no-entry --shared-memory --max-memory=131072 %t1.o -o - | obj2yaml | FileCheck %s --check-prefix SHARED
+
+# RUN: not wasm-ld --no-entry --features=atomics %t1.o -o - 2>&1 | FileCheck %s --check-prefix ATOMICS-NO-SHARED
+
+# RUN: not wasm-ld --no-entry --features=atomics --shared-memory %t1.o -o - 2>&1 | FileCheck %s --check-prefix ATOMICS-NO-MAX
+
+# RUN: not wasm-ld --no-entry --features=atomics --shared-memory --max-memory=100000 %t1.o -o - 2>&1 | FileCheck %s --check-prefix ATOMICS-UNALIGNED
+
+# RUN: wasm-ld --no-entry --features=atomics --shared-memory --max-memory=131072 %t1.o -o - | obj2yaml | FileCheck %s --check-prefix SHARED
+
+
+--- !WASM
+FileHeader:
+  Version:         0x00000001
+Sections:
+  - Type:            IMPORT
+    Imports:
+      - Module:          env
+        Field:           __linear_memory
+        Kind:            MEMORY
+        Memory:
+          Initial:         0x00000001
+      - Module:          env
+        Field:           __indirect_function_table
+        Kind:            TABLE
+        Table:
+          ElemType:        FUNCREF
+          Limits:
+            Initial:         0x00000000
+  - Type:            DATA
+    Segments:
+      - SectionOffset:   6
+        InitFlags:       0
+        Offset:
+          Opcode:          I32_CONST
+          Value:           0
+        Content:         68656C6C6F0A00
+  - Type:            CUSTOM
+    Name:            linking
+    Version:         2
+    SymbolTable:
+      - Index:           0
+        Kind:            DATA
+        Name:            hello_str
+        Flags:           [  ]
+        Segment:         0
+        Size:            7
+    SegmentInfo:
+      - Index:           0
+        Name:            .rodata.hello_str
+        Alignment:       0
+        Flags:           [  ]
+...
+
+# SHARED-NO-MAX: maximum memory too small, 66560 bytes needed{{$}}
+
+# SHARED-UNALIGNED: maximum memory must be 65536-byte aligned{{$}}
+
+# SHARED:        - Type:            MEMORY
+# SHARED-NEXT:     Memories:
+# SHARED-NEXT:       - Flags:           [ HAS_MAX, IS_SHARED ]
+# SHARED-NEXT:         Initial:         0x00000002
+# SHARED-NEXT:         Maximum:         0x00000002
+
+# ATOMICS-NO-SHARED: 'atomics' feature is used, so --shared-memory must be used{{$}}
+
+# ATOMICS-NO-MAX: maximum memory too small, 66560 bytes needed{{$}}
+
+# ATOMICS-UNALIGNED: maximum memory must be 65536-byte aligned{{$}}
Index: lld/trunk/wasm/Writer.cpp
===================================================================
--- lld/trunk/wasm/Writer.cpp
+++ lld/trunk/wasm/Writer.cpp
@@ -169,7 +169,7 @@
     Import.Kind = WASM_EXTERNAL_MEMORY;
     Import.Memory.Flags = 0;
     Import.Memory.Initial = NumMemoryPages;
-    if (MaxMemoryPages != 0) {
+    if (MaxMemoryPages != 0 || Config->SharedMemory) {
       Import.Memory.Flags |= WASM_LIMITS_FLAG_HAS_MAX;
       Import.Memory.Maximum = MaxMemoryPages;
     }
@@ -257,7 +257,7 @@
   SyntheticSection *Section = createSyntheticSection(WASM_SEC_MEMORY);
   raw_ostream &OS = Section->getStream();
 
-  bool HasMax = MaxMemoryPages != 0;
+  bool HasMax = MaxMemoryPages != 0 || Config->SharedMemory;
   writeUleb128(OS, 1, "memory count");
   unsigned Flags = 0;
   if (HasMax)
@@ -831,7 +831,8 @@
   NumMemoryPages = alignTo(MemoryPtr, WasmPageSize) / WasmPageSize;
   log("mem: total pages = " + Twine(NumMemoryPages));
 
-  if (Config->MaxMemory != 0) {
+  // Check max if explicitly supplied or required by shared memory
+  if (Config->MaxMemory != 0 || Config->SharedMemory) {
     if (Config->MaxMemory != alignTo(Config->MaxMemory, WasmPageSize))
       error("maximum memory must be " + Twine(WasmPageSize) + "-byte aligned");
     if (MemoryPtr > Config->MaxMemory)
@@ -927,9 +928,16 @@
   if (InferFeatures)
     TargetFeatures.insert(Used.begin(), Used.end());
 
+  if (TargetFeatures.count("atomics") && !Config->SharedMemory)
+    error("'atomics' feature is used, so --shared-memory must be used");
+
   if (!Config->CheckFeatures)
     return;
 
+  if (Disallowed.count("atomics") && Config->SharedMemory)
+    error(
+        "'atomics' feature is disallowed, so --shared-memory must not be used");
+
   // Validate that used features are allowed in output
   if (!InferFeatures) {
     for (auto &Feature : Used) {