[wasm] [debug] Add support for global variables

When instantiating the wasm interpreter, pass the start address of the
global variables. This was nullptr before, leading to a crash if
debugging a program which accesses globals.
With test.

R=ahaas@chromium.org, titzer@chromium.org
BUG=v8:5822

Change-Id: I5f419790042ef9a00787df093a07e5e5835d55bd
Reviewed-on: https://chromium-review.googlesource.com/456219
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43948}

src/wasm/wasm-debug.cc

@@ -73,6 +73,10 @@ class InterpreterHandle {
       instance_.mem_start = nullptr;
       instance_.mem_size = 0;
     }
+    if (debug_info->wasm_instance()->has_globals_buffer()) {
+      instance_.globals_start = reinterpret_cast<byte*>(
+          debug_info->wasm_instance()->globals_buffer()->backing_store());
+    }
     if (instance_.module->num_imported_functions > 0) {
       int num_imported_functions =
           static_cast<int>(instance_.module->num_imported_functions);

test/mjsunit/wasm/interpreter.js

@@ -139,3 +139,52 @@ function checkStack(stack, expected_lines) {
     ]);
   }
 })();
+
+(function testGlobals() {
+  var builder = new WasmModuleBuilder();
+  builder.addGlobal(kWasmI32, true);  // 0
+  builder.addGlobal(kWasmI64, true);  // 1
+  builder.addGlobal(kWasmF32, true);  // 2
+  builder.addGlobal(kWasmF64, true);  // 3
+  builder.addFunction('get_i32', kSig_i_v)
+      .addBody([kExprGetGlobal, 0])
+      .exportFunc();
+  builder.addFunction('get_i64', kSig_d_v)
+      .addBody([kExprGetGlobal, 1, kExprF64SConvertI64])
+      .exportFunc();
+  builder.addFunction('get_f32', kSig_d_v)
+      .addBody([kExprGetGlobal, 2, kExprF64ConvertF32])
+      .exportFunc();
+  builder.addFunction('get_f64', kSig_d_v)
+      .addBody([kExprGetGlobal, 3])
+      .exportFunc();
+  builder.addFunction('set_i32', kSig_v_i)
+      .addBody([kExprGetLocal, 0, kExprSetGlobal, 0])
+      .exportFunc();
+  builder.addFunction('set_i64', kSig_v_d)
+      .addBody([kExprGetLocal, 0, kExprI64SConvertF64, kExprSetGlobal, 1])
+      .exportFunc();
+  builder.addFunction('set_f32', kSig_v_d)
+      .addBody([kExprGetLocal, 0, kExprF32ConvertF64, kExprSetGlobal, 2])
+      .exportFunc();
+  builder.addFunction('set_f64', kSig_v_d)
+      .addBody([kExprGetLocal, 0, kExprSetGlobal, 3])
+      .exportFunc();
+  var instance = builder.instantiate();
+  // Initially, all should be zero.
+  assertEquals(0, instance.exports.get_i32());
+  assertEquals(0, instance.exports.get_i64());
+  assertEquals(0, instance.exports.get_f32());
+  assertEquals(0, instance.exports.get_f64());
+  // Assign values to all variables.
+  var values = [4711, 1<<40 + 1 << 33, 0.3, 12.34567];
+  instance.exports.set_i32(values[0]);
+  instance.exports.set_i64(values[1]);
+  instance.exports.set_f32(values[2]);
+  instance.exports.set_f64(values[3]);
+  // Now check the values.
+  assertEquals(values[0], instance.exports.get_i32());
+  assertEquals(values[1], instance.exports.get_i64());
+  assertEqualsDelta(values[2], instance.exports.get_f32(), 2**-23);
+  assertEquals(values[3], instance.exports.get_f64());
+})();