From b5c747851c82ca4b862d4f2e278565ca46d95c72 Mon Sep 17 00:00:00 2001
From: Aizal Khan <aizumusheer2@gmail.com>
Date: Sun, 27 Sep 2026 08:14:11 +0530
Subject: [PATCH 1/2] Trap on argument count mismatch in DefinedFunc::DoCall

---
 src/interp/interp-util.cc |  6 ++++--
 src/interp/interp.cc      | 10 +++++++++-
 src/test-interp.cc        | 20 ++++++++++++++++++++
 3 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/src/interp/interp-util.cc b/src/interp/interp-util.cc
index 3d21d6d099..b6b16442d8 100644
--- a/src/interp/interp-util.cc
+++ b/src/interp/interp-util.cc
@@ -16,6 +16,7 @@
 
 #include "wabt/interp/interp-util.h"
 
+#include <algorithm>
 #include <cinttypes>
 
 #include "wabt/stream.h"
@@ -84,9 +85,10 @@ void WriteValues(Stream* stream,
                  const ValueTypes& types,
                  const Values& values) {
   assert(types.size() == values.size());
-  for (size_t i = 0; i < values.size(); ++i) {
+  size_t count = std::min(types.size(), values.size());
+  for (size_t i = 0; i < count; ++i) {
     WriteValue(stream, TypedValue{types[i], values[i]});
-    if (i != values.size() - 1) {
+    if (i != count - 1) {
       stream->Writef(", ");
     }
   }
diff --git a/src/interp/interp.cc b/src/interp/interp.cc
index ff869e06c7..c457b84b18 100644
--- a/src/interp/interp.cc
+++ b/src/interp/interp.cc
@@ -537,7 +537,15 @@ Result DefinedFunc::DoCall(Thread& thread,
                            const Values& params,
                            Values& results,
                            Trap::Ptr* out_trap) {
-  assert(params.size() == type_.params.size());
+  if (params.size() != type_.params.size()) {
+    *out_trap =
+        Trap::New(thread.store(),
+                  StringPrintf("argument count mismatch: expected %" PRIindex
+                               ", got %" PRIindex,
+                               static_cast<Index>(type_.params.size()),
+                               static_cast<Index>(params.size())));
+    return Result::Error;
+  }
   thread.PushValues(type_.params, params);
   RunResult result = thread.PushCall(*this, out_trap);
   if (result == RunResult::Trap) {
diff --git a/src/test-interp.cc b/src/test-interp.cc
index 272676f77e..cbf2e7bbcc 100644
--- a/src/test-interp.cc
+++ b/src/test-interp.cc
@@ -174,6 +174,26 @@ TEST_F(InterpTest, Fac) {
   EXPECT_EQ(120u, results[0].Get<u32>());
 }
 
+TEST_F(InterpTest, CallArgCountMismatch) {
+  // (module (func (export "f") (param i32) (result i32) local.get 0))
+  ReadModule({
+      0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00, 0x01, 0x06, 0x01, 0x60,
+      0x01, 0x7f, 0x01, 0x7f, 0x03, 0x02, 0x01, 0x00, 0x07, 0x05, 0x01, 0x01,
+      0x66, 0x00, 0x00, 0x0a, 0x06, 0x01, 0x04, 0x00, 0x20, 0x00, 0x0b,
+  });
+  Instantiate();
+  auto func = GetFuncExport(0);
+
+  // Calling with fewer arguments than the function has parameters must trap
+  // rather than read past the end of the params vector.
+  Values results;
+  Trap::Ptr trap;
+  Result result = func->Call(store_, {}, results, &trap);
+
+  ASSERT_EQ(Result::Error, result);
+  ASSERT_TRUE(trap);
+}
+
 TEST_F(InterpTest, Fac_Trace) {
   ReadModule(s_fac_module);
   Instantiate();

From 15a8333525832f40a7cd62308947fd95100b7b00 Mon Sep 17 00:00:00 2001
From: Aizal Khan <aizumusheer2@gmail.com>
Date: Thu, 1 Oct 2026 14:07:45 +0530
Subject: [PATCH 2/2] Reuse the existing fac module in the arity mismatch test

---
 src/test-interp.cc | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/src/test-interp.cc b/src/test-interp.cc
index cbf2e7bbcc..92e0cc8d1a 100644
--- a/src/test-interp.cc
+++ b/src/test-interp.cc
@@ -175,17 +175,12 @@ TEST_F(InterpTest, Fac) {
 }
 
 TEST_F(InterpTest, CallArgCountMismatch) {
-  // (module (func (export "f") (param i32) (result i32) local.get 0))
-  ReadModule({
-      0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00, 0x01, 0x06, 0x01, 0x60,
-      0x01, 0x7f, 0x01, 0x7f, 0x03, 0x02, 0x01, 0x00, 0x07, 0x05, 0x01, 0x01,
-      0x66, 0x00, 0x00, 0x0a, 0x06, 0x01, 0x04, 0x00, 0x20, 0x00, 0x0b,
-  });
+  ReadModule(s_fac_module);
   Instantiate();
   auto func = GetFuncExport(0);
 
-  // Calling with fewer arguments than the function has parameters must trap
-  // rather than read past the end of the params vector.
+  // Calling the one-parameter export with no arguments must trap rather than
+  // read past the end of the params vector.
   Values results;
   Trap::Ptr trap;
   Result result = func->Call(store_, {}, results, &trap);