[WASM] Implements catch for the wasm low level exception mechanism.

test/mjsunit/wasm/exceptions.js

 // Copyright 2015 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: --expose-wasm --wasm-eh-prototype
 
 load("test/mjsunit/wasm/wasm-constants.js");
 load("test/mjsunit/wasm/wasm-module-builder.js");
 
-var module = (function () {
+// The following methods do not attempt to catch the exception they raise.
+var test_throw = (function () {
   var builder = new WasmModuleBuilder();
 
-  builder.addFunction("throw_param_if_not_zero", kSig_i_i)
-    .addBody([
-      kExprGetLocal, 0,
-      kExprI32Const, 0,
-      kExprI32Ne,
-      kExprIf,
-      kExprGetLocal, 0,
-      kExprThrow,
-      kExprEnd,
-      kExprI32Const, 1
-    ])
-    .exportFunc()
-
-  builder.addFunction("throw_20", kSig_v_v)
-    .addBody([
-      kExprI32Const, 20,
-      kExprThrow
-    ])
-    .exportFunc()
-
-  builder.addFunction("throw_expr_with_params", kSig_v_ddi)
-    .addBody([
-      // p2 * (p0 + min(p0, p1))|0 - 20
-      kExprGetLocal, 2,
-      kExprGetLocal, 0,
-      kExprGetLocal, 0,
-      kExprGetLocal, 1,
-      kExprF64Min,
-      kExprF64Add,
-      kExprI32SConvertF64,
-      kExprI32Mul,
-      kExprI32Const, 20,
-      kExprI32Sub,
-      kExprThrow
-    ])
-    .exportFunc()
-
-  return builder.instantiate();
+    function always() {
+      throw 50;
+    }
+
+    var sig_index = builder.addType(kSig_v_v);
+    builder.addImport("_0", sig_index);
+
+    builder.addFunction("throw_param_if_not_zero", kSig_i_i)
+      .addBody([
+        kExprGetLocal, 0,
+        kExprI32Const, 0,
+        kExprI32Ne,
+        kExprIf,
+        kExprGetLocal, 0,
+        kExprThrow,
+        kExprEnd,
+        kExprI32Const, 1
+      ])
+      .exportFunc()
+
+    builder.addFunction("throw_20", kSig_i_v)
+      .addBody([
+        kExprI32Const, 20,
+        kExprThrow,
+        kExprI32Const, 0
+      ])
+      .exportFunc()
+
+    builder.addFunction("throw_expr_with_params", kSig_v_ddi)
+      .addBody([
+        // p2 * (p0 + min(p0, p1))|0 - 20
+        kExprGetLocal, 2,
+        kExprGetLocal, 0,
+        kExprGetLocal, 0,
+        kExprGetLocal, 1,
+        kExprF64Min,
+        kExprF64Add,
+        kExprI32SConvertF64,
+        kExprI32Mul,
+        kExprI32Const, 20,
+        kExprI32Sub,
+        kExprThrow
+      ])
+      .exportFunc()
+
+  return builder.instantiate({_0: always});
 })();
 
-// Check the module exists.
-assertFalse(module === undefined);
-assertFalse(module === null);
-assertFalse(module === 0);
-assertEquals("object", typeof module.exports);
-assertEquals("function", typeof module.exports.throw_param_if_not_zero);
-
-assertEquals(1, module.exports.throw_param_if_not_zero(0));
-assertWasmThrows(10, function() { module.exports.throw_param_if_not_zero(10) });
-assertWasmThrows(-1, function() { module.exports.throw_param_if_not_zero(-1) });
-assertWasmThrows(20, module.exports.throw_20);
+// Check the test_throw exists.
+assertFalse(test_throw === undefined);
+assertFalse(test_throw === null);
+assertFalse(test_throw === 0);
+assertEquals("object", typeof test_throw.exports);
+assertEquals("function", typeof test_throw.exports.throw_param_if_not_zero);
+assertEquals("function", typeof test_throw.exports.throw_20);
+assertEquals("function", typeof test_throw.exports.throw_expr_with_params);
+
+assertEquals(1, test_throw.exports.throw_param_if_not_zero(0));
+assertWasmThrows(10, function() { test_throw.exports.throw_param_if_not_zero(10) });
+assertWasmThrows(-1, function() { test_throw.exports.throw_param_if_not_zero(-1) });
+assertWasmThrows(20, test_throw.exports.throw_20);
 assertWasmThrows(
-    -8, function() { module.exports.throw_expr_with_params(1.5, 2.5, 4); });
+    -8, function() { test_throw.exports.throw_expr_with_params(1.5, 2.5, 4); });
 assertWasmThrows(
-    12, function() { module.exports.throw_expr_with_params(5.7, 2.5, 4); });
+    12, function() { test_throw.exports.throw_expr_with_params(5.7, 2.5, 4); });
+
+
+// Now that we know throwing works, we test catching the exceptions we raise.
+var test_catch = (function () {
+  var builder = new WasmModuleBuilder();
+
+    function LEB128(value, size) {
+      let bytes = [];
+
+      let more = 1;
+      let negative = (value < 0);
+      while(more) {
+        b = value & 0x7f; // low order 7 bits of value;
+        value >>= 7;
+
+        /* sign bit of byte is second high order bit (0x40) */
+        if (((value == 0) && ((b & 0x40) == 0)) ||
+            ((value == -1) && ((b & 0x40) != 0)))
+          more = 0;
+        else
+          b |= 0x80;
+        bytes = bytes.concat([b]);
+      }
+
+      return bytes;
+    }
+
+    function varint32(value) {
+      let kBitsInI32 = 32;
+      return LEB128(value, kBitsInI32);
+    }
+
+    // Helper function for throwing from Wasm.
+    var kWasmThrowFunction =
+      builder.addFunction("throw", kSig_v_i)
+        .addBody([
+          kExprGetLocal, 0,
+          kExprThrow
+        ])
+        .index;
+
+    // Helper function for throwing from js. It is imported by the Wasm module
+    // as throw_i.
+    function throw_value(value) {
+      throw value;
+    }
+    var sig_index = builder.addType(kSig_v_i);
+    var kJSThrowI = builder.addImport("throw_i", sig_index);
+
+    // Helper function that throws a string. Wasm should not catch it.
+    function throw_string() {
+      throw "use wasm;";
+    }
+    sig_index = builder.addType(kSig_v_v);
+    var kJSThrowString = builder.addImport("throw_string", sig_index);
+
+    // Helper function that throws undefined. Wasm should not catch it.
+    function throw_undefined() {
+      throw undefined;
+    }
+    var kJSThrowUndefined = builder.addImport("throw_undefined", sig_index);
+
+    // Helper function that throws an fp. Wasm should not catch it.
+    function throw_fp() {
+      throw 10.5;
+    }
+    var kJSThrowFP = builder.addImport("throw_fp", sig_index);
+
+    // Helper function that throws a large number. Wasm should not catch it.
+    function throw_large() {
+      throw 1e+28;
+    }
+    var kJSThrowLarge = builder.addImport("throw_large", sig_index);
+
+    // Scenario 1: Throw and catch appear on the same function. This should
+    // happen in case of inlining, for example.
+    builder.addFunction("same_scope", kSig_i_i)
+      .addBody([
+        kExprTry,
+        kExprGetLocal, 0,
+        kExprI32Const, 0,
+        kExprI32Ne,
+        kExprIf,
+        kExprGetLocal, 0,
+        kExprThrow,
+        kExprEnd,
+        kExprI32Const, 63,
+        kExprCatch, 1,
+        kExprGetLocal, 1,
+        kExprEnd
+      ])
+      .addLocals({i32_count: 1})
+      .exportFunc()
+      .index;
+
+    builder.addFunction("same_scope_ignore", kSig_i_i)
+      .addBody([
+          kExprTry,
+            kExprGetLocal, 0,
+            kExprThrow,
+            kExprUnreachable,
+          kExprCatch, 1,
+            kExprGetLocal, 0,
+          kExprEnd,
+      ])
+      .addLocals({i32_count: 1})
+      .exportFunc();
+
+    builder.addFunction("same_scope_multiple", kSig_i_i)
+      // path = 0;
+      //
+      // try {
+      //   try {
+      //     try {
+      //       if (p == 1)
+      //         throw 1;
+      //       path |= 2
+      //     } catch (v) {
+      //       path |= v | 4;
+      //       throw path;
+      //     }
+      //     if (p == 2)
+      //       throw path|8;
+      //     path |= 16;
+      //   } catch (v) {
+      //     path |= v | 32;
+      //     throw path;
+      //   }
+      //   if (p == 3)
+      //     throw path|64;
+      //   path |= 128
+      // } catch (v) {
+      //   path |= v | 256;
+      // }
+      //
+      // return path;
+      //
+      // p == 1 -> path == 293
+      // p == 2 -> path == 298
+      // p == 3 -> path == 338
+      // else   -> path == 146
+      .addBody([
+          kExprTry,

[bradnelson, 2016/09/27 04:25:56]

Shame how verbose these are.
We've been chatting about adding a more ergonomic / clever assembler for wasm in
C++.
Something in JS might be nice too.
Sigh (nothing for you to do here).

[John, 2016/09/28 13:37:18]

Acknowledged.

+            kExprTry,
+              kExprTry,
+                kExprGetLocal, 0,
+                kExprI32Const, 1,
+                kExprI32Eq,
+                kExprIf,
+                  kExprI32Const, 1,
+                  kExprThrow,
+                  kExprUnreachable,
+                kExprElse,
+                  kExprI32Const, 2,
+                kExprEnd,
+              kExprCatch, 1,
+                kExprGetLocal, 1,
+                kExprI32Const, 4,
+                kExprI32Ior,
+                kExprThrow,
+                kExprUnreachable,
+              kExprEnd,
+              kExprSetLocal, 2,
+              kExprGetLocal, 0,
+              kExprI32Const, 2,
+              kExprI32Eq,
+              kExprIf,
+                kExprGetLocal, 2,
+                kExprI32Const, 8,
+                kExprI32Ior,
+                kExprThrow,
+                kExprUnreachable,
+              kExprElse,
+                kExprI32Const, 16,
+              kExprEnd,
+              kExprI32Ior,
+            kExprCatch, 1,
+              kExprGetLocal, 1,
+              kExprI32Const, 32,
+              kExprI32Ior,
+              kExprThrow,
+              kExprUnreachable,
+            kExprEnd,
+            kExprSetLocal, 2,
+            kExprGetLocal, 0,
+            kExprI32Const, 3,
+            kExprI32Eq,
+            kExprIf,
+              kExprGetLocal, 2,
+              kExprI32Const].concat(varint32(64)).concat([
+              kExprI32Ior,
+              kExprThrow,
+              kExprUnreachable,
+            kExprElse,
+              kExprI32Const]).concat(varint32(128)).concat([
+            kExprEnd,
+            kExprI32Ior,
+          kExprCatch, 1,
+            kExprGetLocal, 1,
+            kExprI32Const]).concat(varint32(256)).concat([
+            kExprI32Ior,
+          kExprEnd,
+      ]))
+      .addLocals({i32_count: 2})
+      .exportFunc();
+
+    // Scenario 2: Catches an exception raised from the direct callee.
+    var kFromDirectCallee =
+      builder.addFunction("from_direct_callee", kSig_i_i)
+        .addBody([
+          kExprTry,
+            kExprGetLocal, 0,
+            kExprCallFunction, kArity1, kWasmThrowFunction,
+            kExprI32Const].concat(varint32(-1)).concat([
+          kExprCatch, 1,
+            kExprGetLocal, 1,
+          kExprEnd
+        ]))
+        .addLocals({i32_count: 1})
+        .exportFunc()
+        .index;
+
+    // Scenario 3: Catches an exception raised from an indirect callee.
+    var kFromIndirectCalleeHelper = kFromDirectCallee + 1;
+    builder.addFunction("from_indirect_callee_helper", kSig_v_ii)
+      .addBody([
+        kExprGetLocal, 0,
+        kExprI32Const, 0,
+        kExprI32GtS,
+        kExprIf,
+        kExprGetLocal, 0,
+        kExprI32Const, 1,
+        kExprI32Sub,
+        kExprGetLocal, 1,
+        kExprI32Const, 1,
+        kExprI32Sub,
+        kExprCallFunction, kArity2, kFromIndirectCalleeHelper,
+        kExprEnd,
+        kExprGetLocal, 1,
+        kExprCallFunction, kArity1, kWasmThrowFunction
+      ]);
+
+    builder.addFunction("from_indirect_callee", kSig_i_i)
+      .addBody([
+        kExprTry,
+          kExprGetLocal, 0,
+          kExprI32Const, 0,
+          kExprCallFunction, kArity2, kFromIndirectCalleeHelper,
+          kExprI32Const].concat(varint32(-1)).concat([

[titzer, 2016/09/28 12:53:31]

The concats here are a little messy. Maybe just always output the 5-byte version
of a constant?

[John, 2016/09/28 13:37:18]

Done.

+        kExprCatch, 1,
+          kExprGetLocal, 1,
+        kExprEnd
+      ]))
+      .addLocals({i32_count: 1})
+      .exportFunc();
+
+    // Scenario 4: Catches an exception raised in JS.
+    builder.addFunction("from_js", kSig_i_i)
+      .addBody([
+        kExprTry,
+          kExprGetLocal, 0,
+          kExprCallImport, kArity1, kJSThrowI,
+          kExprI32Const].concat(varint32(-1)).concat([
+        kExprCatch, 1,
+          kExprGetLocal, 1,
+        kExprEnd,
+      ]))
+      .addLocals({i32_count: 1})
+      .exportFunc();
+
+    // Scenario 5: Does not catch an exception raised in JS if it is not a
+    // number.
+    builder.addFunction("string_from_js", kSig_v_v)
+      .addBody([
+          kExprCallImport, kArity0, kJSThrowString,
+      ])
+      .exportFunc();
+
+    builder.addFunction("fp_from_js", kSig_v_v)
+      .addBody([
+          kExprCallImport, kArity0, kJSThrowFP,
+      ])
+      .exportFunc();
+
+    builder.addFunction("large_from_js", kSig_v_v)
+      .addBody([
+          kExprCallImport, kArity0, kJSThrowLarge,
+      ])
+      .exportFunc();
+
+    builder.addFunction("undefined_from_js", kSig_v_v)
+      .addBody([
+          kExprCallImport, kArity0, kJSThrowUndefined,
+      ])
+      .exportFunc();
+
+  return builder.instantiate({
+      throw_i: throw_value,
+      throw_string: throw_string,
+      throw_fp: throw_fp,
+      throw_large, throw_large,
+      throw_undefined: throw_undefined
+  });
+})();
+
+// Check the test_catch exists.
+assertFalse(test_catch === undefined);
+assertFalse(test_catch === null);
+assertFalse(test_catch === 0);
+assertEquals("object", typeof test_catch.exports);
+assertEquals("function", typeof test_catch.exports.same_scope);
+assertEquals("function", typeof test_catch.exports.same_scope_ignore);
+assertEquals("function", typeof test_catch.exports.same_scope_multiple);
+assertEquals("function", typeof test_catch.exports.from_direct_callee);
+assertEquals("function", typeof test_catch.exports.from_indirect_callee);
+assertEquals("function", typeof test_catch.exports.from_js);
+assertEquals("function", typeof test_catch.exports.string_from_js);
+
+assertEquals(63, test_catch.exports.same_scope(0));
+assertEquals(1024, test_catch.exports.same_scope(1024));
+assertEquals(-3, test_catch.exports.same_scope(-3));
+assertEquals(1024, test_catch.exports.same_scope_ignore(1024));
+assertEquals(0x7FFFFFFF, test_catch.exports.same_scope_ignore(0x7FFFFFFF));
+assertEquals(-1, test_catch.exports.same_scope_ignore(-1));
+assertEquals(293, test_catch.exports.same_scope_multiple(1));
+assertEquals(298, test_catch.exports.same_scope_multiple(2));
+assertEquals(338, test_catch.exports.same_scope_multiple(3));
+assertEquals(146, test_catch.exports.same_scope_multiple(0));
+assertEquals(-10024, test_catch.exports.from_direct_callee(-10024));
+assertEquals(3334333, test_catch.exports.from_direct_callee(3334333));
+assertEquals(-1, test_catch.exports.from_direct_callee(0xFFFFFFFF));
+assertEquals(0x7FFFFFFF, test_catch.exports.from_direct_callee(0x7FFFFFFF));
+assertEquals(-10, test_catch.exports.from_indirect_callee(10));
+assertEquals(-77, test_catch.exports.from_indirect_callee(77));
+assertEquals(10, test_catch.exports.from_js(10));
+assertEquals(-10, test_catch.exports.from_js(-10));
+
+assertThrowsEquals(test_catch.exports.string_from_js, "use wasm;");
+assertThrowsEquals(test_catch.exports.large_from_js, 1e+28);
+assertThrowsEquals(test_catch.exports.undefined_from_js, undefined);