Wasm2c fuzz support: only emit a call to the hang limit function if present (#2977)

It may not be present while reducing a testcase, if the reducer removed it.

3 files changed, 28 insertions, 2 deletions

diff --git a/src/tools/wasm2c-wrapper.h b/src/tools/wasm2c-wrapper.h
index 55eed0c35..b3205c6fe 100644
--- a/src/tools/wasm2c-wrapper.h
+++ b/src/tools/wasm2c-wrapper.h
@@ -85,9 +85,14 @@ int main(int argc, char** argv) {
   // wasm traps, and emitting a single one helps compilation speed into wasm as
   // compile times are O(size * num_setjmps).
   for (size_t curr = 0;; curr++) {
-    // Always call the hang limit initializer before each export.
+  )";
+  if (wasm.getExportOrNull("hangLimitInitializer")) {
+    ret += R"(
+    // If present, call the hang limit initializer before each export.
     (*Z_hangLimitInitializerZ_vv)();
-
+)";
+  }
+  ret += R"(
     // Prepare to call the export, so we can catch traps.
     if (WASM_RT_SETJMP(g_jmp_buf) != 0) {
       puts("exception!");
diff --git a/test/unit/input/empty.wasm b/test/unit/input/empty.wasm
new file mode 100644
index 000000000..d8fc92d02
--- /dev/null
+++ b/test/unit/input/empty.wasm
diff --git a/test/unit/test_wasm2c.py b/test/unit/test_wasm2c.py
new file mode 100644
index 000000000..bcdab355b
--- /dev/null
+++ b/test/unit/test_wasm2c.py
@@ -0,0 +1,21 @@
+from scripts.test import shared
+from . import utils
+
+
+class Wasm2CTest(utils.BinaryenTestCase):
+    def test_wrapper(self):
+        # the wrapper C code should only call the hang limit initializer if
+        # that is present.
+        empty_wasm = self.input_path('empty.wasm')
+        args = [empty_wasm, '--emit-wasm2c-wrapper=output.c']
+        shared.run_process(shared.WASM_OPT + args)
+        with open('output.c') as f:
+            normal_output = f.read()
+        # running with ttf generates a new wasm for fuzzing, which always
+        # includes the hang limit initializer function
+        shared.run_process(shared.WASM_OPT + args + ['-ttf'])
+        with open('output.c') as f:
+            ttf_output = f.read()
+        hang_limit_name = 'hangLimitInitializer'
+        self.assertIn(hang_limit_name, ttf_output)
+        self.assertNotIn(hang_limit_name, normal_output)