[wasm] Base address for data segments can also be the value of a global variable.

test/mjsunit/wasm/wasm-module-builder.js

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Used for encoding f32 and double constants to bits.
 let __buffer = new ArrayBuffer(8);
 let byte_view = new Int8Array(__buffer);
 let f32_view = new Float32Array(__buffer);
 let f64_view = new Float64Array(__buffer);
 
@@ skipping 181 matching lines @@
              mutable: false}
     this.imports.push(o);
     return this.num_imported_globals++;
   }
 
   addImportedMemory(module, name, initial = 0, maximum) {
     let o = {module: module, name: name, kind: kExternalMemory, initial: initial, maximum: maximum};
     this.imports.push(o);
   }
 
-  addDataSegment(addr, data, init) {
-    this.segments.push({addr: addr, data: data, init: init});
+  addDataSegment(addr, data, is_global = false) {
+    this.segments.push({addr: addr, data: data, is_global: is_global});
     return this.segments.length - 1;
   }
 
   exportMemoryAs(name) {
     this.exports.push({name: name, kind: kExternalMemory, index: 0});
   }
 
   appendToTable(array) {
     this.table.push(...array);
     return this;
@@ skipping 223 matching lines @@
       });
     }
 
     // Add data segments.
     if (wasm.segments.length > 0) {
       if (debug) print("emitting data segments @ " + binary.length);
       binary.emit_section(kDataSectionCode, section => {
         section.emit_u32v(wasm.segments.length);
         for (let seg of wasm.segments) {
           section.emit_u8(0);  // linear memory index 0
-          section.emit_u8(kExprI32Const);
-          section.emit_u32v(seg.addr);
+          if (seg.is_global) {
+            // initializer is a global variable
+            section.emit_u8(kExprGetGlobal);
+            section.emit_u32v(seg.addr);
+          } else {
+            // initializer is a constant
+            section.emit_u8(kExprI32Const);
+            section.emit_u32v(seg.addr);
+          }
           section.emit_u8(kExprEnd);
           section.emit_u32v(seg.data.length);
           section.emit_bytes(seg.data);
         }
       });
     }
 
     // Add any explicitly added sections
     for (let exp of wasm.explicit) {
       if (debug) print("emitting explicit @ " + binary.length);
@@ skipping 28 matching lines @@
     }
     return buffer;
   }
 
   instantiate(...args) {
     let module = new WebAssembly.Module(this.toBuffer());
     let instance = new WebAssembly.Instance(module, ...args);
     return instance;
   }
 }