Fuzzer: Add a flag to avoid emitting invokes (#9212)

By default we emit invoker functions for things, basically new exports
that call functions that might not be called otherwise. This gets more
things to execute. However, in fuzzers like Fuzzilli, we don't want to
add this extra size to things, so add a flag to control it.

Author: kripken

src/tools/fuzzing.h

@@ -133,6 +133,7 @@ class TranslateToFuzzReader {
     preserveImportsAndExports = preserveImportsAndExports_;
   }
   void setAgainstJS(bool againstJS_) { againstJS = againstJS_; }
+  void setNoInvokes(bool noInvokes_) { noInvokes = noInvokes_; }
   void setImportedModule(std::string importedModuleName);
 
   void build();
@@ -165,6 +166,9 @@ class TranslateToFuzzReader {
   // which might cause issues when linked against wasm or used otherwise.
   bool againstJS = false;
 
+  // Whether to avoid emitting invoker functions.
+  bool noInvokes = false;
+
   // An optional module to import from.
   std::optional<Module> importedModule;
 

src/tools/fuzzing/fuzzing.cpp

@@ -2758,6 +2758,10 @@ void TranslateToFuzzReader::dropToLog(Function* func) {
 }
 
 void TranslateToFuzzReader::addInvocations(Function* func) {
+  if (noInvokes) {
+    return;
+  }
+
   Name name = func->name.toString() + std::string("_invoker");
   if (wasm.getFunctionOrNull(name) || wasm.getExportOrNull(name)) {
     return;

src/tools/wasm-opt.cpp

@@ -87,6 +87,7 @@ int main(int argc, const char* argv[]) {
   bool fuzzOOB = true;
   bool fuzzPreserveImportsAndExports = false;
   bool fuzzAgainstJS = false;
+  bool fuzzNoInvokes = false;
   std::string fuzzImport;
   std::string emitSpecWrapper;
   std::string emitWasm2CWrapper;
@@ -219,6 +220,13 @@ For more on how to optimize effectively, see
       WasmOptOption,
       Options::Arguments::Zero,
       [&](Options* o, const std::string& arguments) { fuzzAgainstJS = true; })
+    .add(
+      "--fuzz-no-invokes",
+      "",
+      "do not emit invoker functions in the fuzzer",
+      WasmOptOption,
+      Options::Arguments::Zero,
+      [&](Options* o, const std::string& arguments) { fuzzNoInvokes = true; })
     .add(
       "--fuzz-import",
       "",
@@ -358,6 +366,7 @@ For more on how to optimize effectively, see
     reader.setAllowOOB(fuzzOOB);
     reader.setPreserveImportsAndExports(fuzzPreserveImportsAndExports);
     reader.setAgainstJS(fuzzAgainstJS);
+    reader.setNoInvokes(fuzzNoInvokes);
     if (!fuzzImport.empty()) {
       reader.setImportedModule(fuzzImport);
     }

test/lit/fuzz-no-invokes.wast

@@ -0,0 +1,10 @@
+;; Test the flag to avoid emitting invoker functions in fuzzer generation.
+
+;; Normally we emit invokers.
+;; RUN: wasm-opt %s.dat -all -ttf                   -S -o - | filecheck %s --check-prefix=NORMAL
+;; NORMAL: invoker
+
+;; But not with the flag.
+;; RUN: wasm-opt %s.dat -all -ttf --fuzz-no-invokes -S -o - | filecheck %s --check-prefix=FLAG
+;; FLAG-NOT: invoker
+

test/lit/fuzz-no-invokes.wast.dat

@@ -76,6 +76,9 @@
 ;; CHECK-NEXT:                                                 that assume it is used only from
 ;; CHECK-NEXT:                                                 JS
 ;; CHECK-EMPTY:
+;; CHECK-NEXT:   --fuzz-no-invokes                             do not emit invoker functions in
+;; CHECK-NEXT:                                                 the fuzzer
+;; CHECK-EMPTY:
 ;; CHECK-NEXT:   --fuzz-import                                 a module to use as an import in 
 ;; CHECK-NEXT:                                                 -ttf mode
 ;; CHECK-EMPTY: