diff --git a/lld/wasm/Writer.cpp b/lld/wasm/Writer.cpp
--- a/lld/wasm/Writer.cpp
+++ b/lld/wasm/Writer.cpp
@@ -872,7 +872,20 @@
   std::string bodyContent;
   {
     raw_string_ostream os(bodyContent);
-    writeUleb128(os, 0, "num locals");
+    // With PIC code we cache the flag address in local 0
+    if (config->isPic) {
+      writeUleb128(os, 1, "num local decls");
+      writeUleb128(os, 1, "local count");
+      writeU8(os, WASM_TYPE_I32, "address type");
+      writeU8(os, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
+      writeUleb128(os, WasmSym::memoryBase->getGlobalIndex(), "memory_base");
+      writeI32Const(os, flagAddress, "flag address");
+      writeU8(os, WASM_OPCODE_I32_ADD, "i32.add");
+      writeU8(os, WASM_OPCODE_LOCAL_SET, "local.set");
+      writeUleb128(os, 0, "local 0");
+    } else {
+      writeUleb128(os, 0, "num locals");
+    }
 
     if (hasPassiveInitializedSegments()) {
       // Initialize memory in a thread-safe manner. The thread that successfully
@@ -916,9 +929,21 @@
       //  )
       //  ( ... drop data segments ... )
       // )
+      //
+      // In the case we are building with PIC the calculate the
+      // flag location using:
+      //
+      //    (global.get $__memory_base)
+      //    (i32.const $__init_memory_flag)
+      //    (i32.const 1)
 
       // Atomically check whether this is the main thread.
-      writeI32Const(os, flagAddress, "flag address");
+      if (config->isPic) {
+        writeU8(os, WASM_OPCODE_LOCAL_GET, "local.get");
+        writeUleb128(os, 0, "local 0");
+      } else {
+        writeI32Const(os, flagAddress, "flag address");
+      }
       writeI32Const(os, 0, "expected flag value");
       writeI32Const(os, 1, "flag value");
       writeU8(os, WASM_OPCODE_ATOMICS_PREFIX, "atomics prefix");
@@ -928,7 +953,12 @@
       writeU8(os, WASM_TYPE_NORESULT, "blocktype");
 
       // Did not increment 0, so wait for main thread to initialize memory
-      writeI32Const(os, flagAddress, "flag address");
+      if (config->isPic) {
+        writeU8(os, WASM_OPCODE_LOCAL_GET, "local.get");
+        writeUleb128(os, 0, "local 0");
+      } else {
+        writeI32Const(os, flagAddress, "flag address");
+      }
       writeI32Const(os, 1, "expected flag value");
       writeI64Const(os, -1, "timeout");
       writeU8(os, WASM_OPCODE_ATOMICS_PREFIX, "atomics prefix");
@@ -948,6 +978,12 @@
             writeI32Const(os, static_cast<int32_t>(s->startVA),
                           "destination address");
           }
+          if (config->isPic) {
+            writeU8(os, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
+            writeUleb128(os, WasmSym::memoryBase->getGlobalIndex(),
+                         "memory_base");
+            writeU8(os, WASM_OPCODE_I32_ADD, "i32.add");
+          }
           // source segment offset
           writeI32Const(os, 0, "segment offset");
           // memory region size
@@ -961,14 +997,24 @@
       }
 
       // Set flag to 2 to mark end of initialization
-      writeI32Const(os, flagAddress, "flag address");
+      if (config->isPic) {
+        writeU8(os, WASM_OPCODE_LOCAL_GET, "local.get");
+        writeUleb128(os, 0, "local 0");
+      } else {
+        writeI32Const(os, flagAddress, "flag address");
+      }
       writeI32Const(os, 2, "flag value");
       writeU8(os, WASM_OPCODE_ATOMICS_PREFIX, "atomics prefix");
       writeUleb128(os, WASM_OPCODE_I32_ATOMIC_STORE, "i32.atomic.store");
       writeMemArg(os, 2, 0);
 
       // Notify any waiters that memory initialization is complete
-      writeI32Const(os, flagAddress, "flag address");
+      if (config->isPic) {
+        writeU8(os, WASM_OPCODE_LOCAL_GET, "local.get");
+        writeUleb128(os, 0, "local 0");
+      } else {
+        writeI32Const(os, flagAddress, "flag address");
+      }
       writeI32Const(os, -1, "number of waiters");
       writeU8(os, WASM_OPCODE_ATOMICS_PREFIX, "atomics prefix");
       writeUleb128(os, WASM_OPCODE_ATOMIC_NOTIFY, "atomic.notify");
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
@@ -263,6 +263,7 @@
   WASM_OPCODE_END = 0x0b,
   WASM_OPCODE_CALL = 0x10,
   WASM_OPCODE_LOCAL_GET = 0x20,
+  WASM_OPCODE_LOCAL_SET = 0x21,
   WASM_OPCODE_GLOBAL_GET = 0x23,
   WASM_OPCODE_GLOBAL_SET = 0x24,
   WASM_OPCODE_I32_STORE = 0x36,