Fuzzer: Log exported globals

scripts/fuzz_opt.py

@@ -1370,14 +1370,24 @@ class CtorEval(TestCaseHandler):
     frequency = 0.1
 
     def handle(self, wasm):
-        # get the expected execution results.
-        wasm_exec = run_bynterp(wasm, ['--fuzz-exec-before'])
-
         # get the list of func exports, so we can tell ctor-eval what to eval.
-        ctors = ','.join(get_exports(wasm, ['func']))
+        func_exports = get_exports(wasm, ['func'])
+        ctors = ','.join(func_exports)
         if not ctors:
             return
 
+        # The fuzzer evaluates exports in the order they are given, so if there
+        # are global exports it may read them before the ctors are run - but
+        # the ctors are meant to run before anything else, and can modify
+        # those global values. Keep only function exports to avoid this
+        # confusion.
+        filtered = wasm + '.filtered.wasm'
+        filter_exports(wasm, filtered, func_exports)
+        wasm = filtered
+
+        # get the expected execution results.
+        wasm_exec = run_bynterp(wasm, ['--fuzz-exec-before'])
+
         # Fix escaping of the names, as we will be passing them as commandline
         # parameters below (e.g. we want --ctors=foo\28bar and not
         # --ctors=foo\\28bar; that extra escaping \ would cause an error).
@@ -1871,7 +1881,8 @@ def handle(self, wasm):
 
         # Make sure that we actually executed all exports from both
         # wasm files.
-        exports = get_exports(wasm, ['func']) + get_exports(second_wasm, ['func'])
+        exports = get_exports(wasm, ['func', 'global'])
+        exports += get_exports(second_wasm, ['func', 'global'])
         calls_in_output = output.count(FUZZ_EXEC_CALL_PREFIX)
         if calls_in_output == 0:
             print(f'warning: no calls in output. output:\n{output}')

scripts/fuzz_shell.js

@@ -198,6 +198,11 @@ function callFunc(func) {
   return func.apply(null, args);
 }
 
+// wasm2js does not define RuntimeError, so use that to check for it. wasm2js
+// overrides the entire WebAssembly object with a polyfill, so we know exactly
+// what it contains, and we need to handle some things differently below.
+var wasm2js = !WebAssembly.RuntimeError;
+
 // Calls a given function in a try-catch. Return 1 if an exception was thrown.
 // If |rethrow| is set, and an exception is thrown, it is caught and rethrown.
 // Wasm traps are not swallowed (see details below).
@@ -213,11 +218,7 @@ function callFunc(func) {
 
     // We only want to catch exceptions, not wasm traps: traps should still
     // halt execution. Handling this requires different code in wasm2js, so
-    // check for that first (wasm2js does not define RuntimeError, so use
-    // that for the check - when wasm2js is run, we override the entire
-    // WebAssembly object with a polyfill, so we know exactly what it
-    // contains).
-    var wasm2js = !WebAssembly.RuntimeError;
+    // check for that first.
     if (!wasm2js) {
       // When running native wasm, we can detect wasm traps.
       if (e instanceof WebAssembly.RuntimeError) {
@@ -555,13 +556,53 @@ function build(binary, isSecond) {
       name = e;
       value = exports[e];
     } else {
-      // We are given an object form exportList, which has both a name and a
+      // We are given an object from exportList, which has both a name and a
       // value.
       name = e.name;
       value = e.value;
     }
 
+    // Check for a global. Note we must be careful in wasm2js mode, where we
+    // can't do instanceof here (the wasm polyfill there doesn't have such
+    // things). In wasm2js we strip global exports to avoid needing to handle
+    // them here (using stub-unsupported-js).
+    if (!wasm2js && (value instanceof WebAssembly.Global)) {
+      // We can log a global value and do other operations to check for bugs.
+      // First, do some operations on the Global wrapper itself.
+      JSON.stringify(value);
+      value.foobar;
+
+      // Log it at the right time later using a lambda. Note that we can't just
+      // capture |value| for the lambda, as the loop modifies it.
+      (() => {
+        var global = value;
+        value = () => {
+          // Time to log. Look at the exported value itself, not the global
+          // wrapper.
+          let actualValue;
+          try {
+            actualValue = global.value;
+          } catch (e) {
+            if (e.message.startsWith('get WebAssembly.Global.value')) {
+              // Just log a null instead of a value we cannot access from JS,
+              // like an exnref.
+              actualValue = null;
+            } else {
+              throw e;
+            }
+          }
+          if (typeof actualValue === 'object') {
+            // logRef can do a little more than logValue, so use it when possible.
+            logRef(actualValue);
+          } else {
+            logValue(actualValue);
+          }
+        };
+      })();
+    }
+
     if (typeof value !== 'function') {
+      // Nothing we can call.
       continue;
     }
 

src/passes/RemoveNonJSOps.cpp

@@ -385,7 +385,6 @@ struct StubUnsupportedJSOpsPass
   void visitModule(Module* module) {
     // We remove global exports, as wasm2js doesn't emit them in a fully
     // compatible form yet (they aren't instances of WebAssembly.Global).
-    // Globals.
     std::vector<Name> badExports;
     for (auto& exp : module->exports) {
       if (exp->kind == ExternalKind::Global) {

src/tools/execution-results.h

@@ -487,23 +487,33 @@ struct ExecutionResults {
     // execute all exported methods (that are therefore preserved through
     // opts)
     for (auto& exp : wasm.exports) {
-      if (exp->kind != ExternalKind::Function) {
-        continue;
-      }
-      std::cout << "[fuzz-exec] calling " << exp->name << "\n";
-      auto* func = wasm.getFunction(*exp->getInternalName());
-      FunctionResult ret = run(func, wasm, instance);
-      results[exp->name] = ret;
-      if (auto* values = std::get_if<Literals>(&ret)) {
-        // ignore the result if we hit an unreachable and returned no value
-        if (values->size() > 0) {
-          std::cout << "[fuzz-exec] note result: " << exp->name << " => ";
-          for (auto value : *values) {
-            printValue(value);
-            std::cout << '\n';
+      if (exp->kind == ExternalKind::Function) {
+        std::cout << "[fuzz-exec] calling " << exp->name << "\n";
+        auto* func = wasm.getFunction(*exp->getInternalName());
+        FunctionResult ret = run(func, wasm, instance);
+        results[exp->name] = ret;
+        if (auto* values = std::get_if<Literals>(&ret)) {
+          // ignore the result if we hit an unreachable and returned no value
+          if (values->size() > 0) {
+            std::cout << "[fuzz-exec] note result: " << exp->name << " => ";
+            for (auto value : *values) {
+              printValue(value);
+              std::cout << '\n';
+            }
           }
         }
+      } else if (exp->kind == ExternalKind::Global) {
+        // Log the global's value. (We use "calling" here to match the output
+        // for calls, which simplifies the fuzzer.)
+        std::cout << "[fuzz-exec] calling " << exp->name << "\n";
+        Literals* value = instance.getExportedGlobalOrNull(exp->name);
+        assert(value);
+        assert(value->size() == 1);
+        std::cout << "[LoggingExternalInterface logging ";
+        printValue((*value)[0]);
+        std::cout << "]\n";
       }
+      // Ignore other exports for now. TODO
     }
   }
 

test/lit/exec/fuzzing-api-globals.wast

@@ -0,0 +1,21 @@
+;; Test logging of global exports. We don't do this using update_lit_checks as
+;; global exports confuse the auto-updater.
+
+(module
+ (type $struct (struct))
+
+ (global $global (mut i32) (i32.const 42))
+
+ (global $global-immref anyref (struct.new $struct))
+
+ (export "global" (global $global))
+ (export "global-immref" (global $global-immref))
+)
+
+;; RUN: wasm-opt %s -all --fuzz-exec -o /dev/null 2>&1 | filecheck %s
+
+;; CHECK:      [fuzz-exec] calling global
+;; CHECK-NEXT: [LoggingExternalInterface logging 42]
+;; CHECK-NEXT: [fuzz-exec] calling global-immref
+;; CHECK-NEXT: [LoggingExternalInterface logging object]
+