[wasm] Provide better stack traces for asm.js code

test/mjsunit/wasm/asm-wasm-stack.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.
+
+// Flags: --validate-asm --allow-natives-syntax
+
+var filename = '(?:[^ ]+/)?test/mjsunit/wasm/asm-wasm-stack.js';
+filename = filename.replace(/\//g, '[/\\\\]');
+
+function checkPreformattedStack(e, expected_lines) {
+  print('preformatted stack: ' + e.stack);
+  var lines = e.stack.split('\n');
+  assertEquals(expected_lines.length, lines.length);
+  for (var i = 0; i < lines.length; ++i) {
+    assertMatches(expected_lines[i], lines[i], 'line ' + i);
+  }
+}
+
+function checkFunctionsOnCallsites(e, locations) {
+  var stack = e.stack;
+  print('callsite objects (size ' + stack.length + '):');
+  for (var i = 0; i < stack.length; ++i) {
+    var s = stack[i];
+    print(
+        ' [' + i + '] ' + s.getFunctionName() + ' (' + s.getFileName() + ':' +
+        s.getLineNumber() + ':' + s.getColumnNumber() + ')');
+  }
+  for (var i = 0; i < locations.length; ++i) {
+    var cs = stack[i];
+    assertMatches('^' + filename + '$', cs.getFileName(), 'file name at ' + i);
+    assertEquals(
+        locations[i][0], cs.getFunctionName(), 'function name at ' + i);
+    assertEquals(locations[i][1], cs.getLineNumber(), 'line number at ' + i);
+    assertEquals(
+        locations[i][2], cs.getColumnNumber(), 'column number at ' + i);
+    assertNotNull(cs.getThis(), 'receiver should be global');
+    assertEquals(stack[0].getThis(), cs.getThis(), 'receiver should be global');
+  }
+}
+
+function throwException() {
+  throw new Error('exception from JS');
+}
+
+(function PreformattedStackTraceFromJS() {
+  function generateWasmFromAsmJs(stdlib, foreign, heap) {
+    'use asm';
+    var throwFunc = foreign.throwFunc;
+    function callThrow() {
+      throwFunc();
+    }
+    function redirectFun() {
+      callThrow();
+    }
+    return redirectFun;
+  }
+
+  var fun = generateWasmFromAsmJs(this, {throwFunc: throwException}, undefined);
+  //assertWasm(fun);

[jgruber, 2016/10/11 19:07:40]

Is the commented code here still needed?

[Clemens Hammacher, 2016/10/12 07:37:18]

Fixed already.

+  //assertNoWasm(throwException);
+  try {
+    fun();
+    assertUnreachable('exception should have been thrown');

[jgruber, 2016/10/11 19:07:40]

This pattern may not work as intended - when assertUnreachable throws an
exception, execution continues in the try block. test/mjsunit/stack-trace.js
unfortunately does the same in a couple of cases, and should also be fixed at
some point.

[Clemens Hammacher, 2016/10/12 07:37:19]

Good catch! Fixed it for this test case.

+  } catch (e) {
+    assertInstanceof(e, Error);
+    checkPreformattedStack(e, [
+      '^Error: exception from JS$',
+      '^ *at throwException \\(' + filename + ':42:9\\)$',
+      '^ *at callThrow \\(' + filename + ':50:7\\)$',
+      '^ *at redirectFun \\(' + filename + ':53:7\\)$',
+      '^ *at PreformattedStackTraceFromJS \\(' + filename + ':62:5\\)$',
+      '^ *at ' + filename + ':75:3$'
+    ]);
+  }
+})();
+
+// Collect the Callsite objects instead of just a string.
+Error.prepareStackTrace = function(error, frames) {
+  return frames;
+};
+
+(function CallsiteObjectsFromJS() {
+  function generateWasmFromAsmJs(stdlib, foreign, heap) {

[jgruber, 2016/10/11 19:07:41]

Could you reuse the function from above?

[Clemens Hammacher, 2016/10/12 07:37:19]

Fixed already.

+    'use asm';
+    var throwFunc = foreign.throwFunc;
+    function callThrow() {
+      throwFunc();
+    }
+    function redirectFun() {
+      callThrow();
+    }
+    return redirectFun;
+  }
+
+  var fun = generateWasmFromAsmJs(this, {throwFunc: throwException}, undefined);
+  try {
+    fun();
+    assertUnreachable('exception should have been thrown');
+  } catch (e) {
+    assertInstanceof(e, Error);
+    checkFunctionsOnCallsites(e, [
+      ['throwException', 42, 9],         // --

[jgruber, 2016/10/11 19:07:41]

What are the '// --' comments?

[Clemens Hammacher, 2016/10/12 07:37:19]

They prevent clang format from joining the lines.

+      ['callThrow', 87, 7],              // --
+      ['redirectFun', 90, 7],            // --
+      ['CallsiteObjectsFromJS', 97, 5],  // --
+      [null, 109, 3]
+    ]);
+  }
+})();