add a flag

Author: kripken

scripts/fuzz_opt.py

@@ -1619,7 +1619,12 @@ def optimize(name):
 
         # get the output from the split modules, linking them using JS
         # TODO run liftoff/turboshaft/etc.
-        linked_output = run_d8_wasm(primary, args=[secondary, exports_to_call])
+        args = [
+            secondary,
+            exports_to_call,
+            '--fuzz-split',
+        ]
+        linked_output = run_d8_wasm(primary, args=args)
         linked_output = fix_output(linked_output)
 
         # see D8.can_compare_to_self: we cannot compare optimized outputs if

scripts/fuzz_shell.js

@@ -47,9 +47,25 @@ if (!binary) {
 // passed a final parameter in the form of "exports:X,Y,Z" then we call
 // specifically the exports X, Y, and Z.
 var exportsToCall;
-if (argv.length > 0 && argv[argv.length - 1].startsWith('exports:')) {
-  exportsToCall = argv[argv.length - 1].substr('exports:'.length).split(',');
-  argv.pop();
+
+// Passing --fuzz-split makes us treat the two input files as split off
+// from a single one, and we will run them as that single file (ignoring extra
+// exports from the second one, and from wasm-split itself). This allows us to
+// get the same behavior from split modules as before the split.
+var fuzzSplit = false;
+
+while (argv.length > 0) {
+  var last = argv[argv.length - 1];
+  if (last.startsWith('exports:')) {
+    exportsToCall = last.substr('exports:'.length).split(',');
+    argv.pop();
+    continue;
+  } else if (last.startsWith('--fuzz-split')) {
+    fuzzSplit = true;
+    argv.pop();
+    continue;
+  }
+  break;
 }
 
 // If a second parameter is given, it is a second binary that we will link in
@@ -420,7 +436,7 @@ if (secondBinary) {
 // Compile and instantiate a wasm file. Receives the binary to build, and
 // whether it is the second one.
 function build(binary, second) {
-  if (second) {
+  if (fuzzSplit && second) {
     assert(secondBinary);
     // Provide the primary module's exports to the secondary.
     imports['primary'] = exports;
@@ -437,10 +453,10 @@ function build(binary, second) {
   }
 
   // Do not add the second instance's exports to the list, as that would be
-  // noticeable by calls to call-export-*. When fuzzing, we want the original
-  // module's exports to be provided from the primary module, and it is the only
-  // interface to the outside.
-  if (second) {
+  // noticeable by calls to call-export-*. When fuzzing wasm-split, we want the
+  // original module's exports to be provided from the primary module, and it is
+  // the only interface to the outside.
+  if (fuzzSplit && second) {
     return;
   }
 
@@ -462,7 +478,7 @@ function build(binary, second) {
     value = wrapExportForJSPI(value);
     exports[key] = value;
 
-    if (secondBinary && key.startsWith('__fuzz_split_')) {
+    if (fuzzSplit && key.startsWith('__fuzz_split_')) {
       // We are fuzzing wasm-split, and this is a new export generated by
       // wasm-split. Do not note these exports as callable from call-export*,
       // as they do not match the original pre-split module.

test/lit/node/fuzz_shell_second.wast

@@ -5,6 +5,10 @@
   (func $first (export "first") (result i32)
     (i32.const 42)
   )
+
+  (func $split (export "__fuzz_split_func") (result i32)
+    (i32.const 999)
+  )
 )
 
 ;; Build both files to binary.
@@ -18,6 +22,8 @@
 ;;
 ;; CHECK: [fuzz-exec] calling first
 ;; CHECK: [fuzz-exec] note result: first => 42
+;; CHECK: [fuzz-exec] calling __fuzz_split_func
+;; CHECK: [fuzz-exec] note result: __fuzz_split_func => 999
 ;; CHECK: [fuzz-exec] calling second
 ;; CHECK: [fuzz-exec] note result: second => 1337
 
@@ -29,4 +35,16 @@
 ;; REVERSE: [fuzz-exec] note result: second => 1337
 ;; REVERSE: [fuzz-exec] calling first
 ;; REVERSE: [fuzz-exec] note result: first => 42
+;; REVERSE: [fuzz-exec] calling __fuzz_split_func
+;; REVERSE: [fuzz-exec] note result: __fuzz_split_func => 999
+
+;; Run with --fuzz-split, which does not run exports from the second one,
+;; and also ignores exports starting with "__fuzz_split_"
+;;
+;; RUN: node %S/../../../scripts/fuzz_shell.js %t.wasm %t.second.wasm --fuzz-split | filecheck %s --check-prefix=WASM_SPLIT
+;;
+;; WASM_SPLIT: [fuzz-exec] calling first
+;; WASM_SPLIT: [fuzz-exec] note result: first => 42
+;; WASM_SPLIT-NOT: [fuzz-exec] calling second
+;; WASM_SPLIT-NOT: [fuzz-exec] calling __fuzz_split_func