From 4dca4c8577941af19c75476639b6d7ef6190b97d Mon Sep 17 00:00:00 2001
From: David Wrighton <davidwr@microsoft.com>
Date: Tue, 6 Jan 2026 13:01:15 -0800
Subject: [PATCH] [clr-interp] Fix EmptyThisCall test - Add detection for
 attempting to call function with this call calling convention without
 actually passing a this argument.

---
 src/coreclr/interpreter/compiler.cpp | 25 +++++++++++++++++++++++++
 src/coreclr/interpreter/compiler.h   |  1 +
 2 files changed, 26 insertions(+)

diff --git a/src/coreclr/interpreter/compiler.cpp b/src/coreclr/interpreter/compiler.cpp
index 74f6ddbae385c0..ce9beb419e0a40 100644
--- a/src/coreclr/interpreter/compiler.cpp
+++ b/src/coreclr/interpreter/compiler.cpp
@@ -4248,6 +4248,24 @@ class InterpAsyncCallPeeps
     }
 } AsyncCallPeeps;
 
+void InterpCompiler::CheckForPInvokeThisCallWithNoArgs(CORINFO_SIG_INFO* sigInfo, CORINFO_METHOD_HANDLE methodHnd)
+{
+    if (sigInfo->numArgs == 0)
+    {
+        CorInfoCallConv callConv = (CorInfoCallConv)(sigInfo->callConv & IMAGE_CEE_CS_CALLCONV_MASK);
+        bool isPInvoke = methodHnd != NULL || (callConv != CORINFO_CALLCONV_DEFAULT && callConv != CORINFO_CALLCONV_VARARG);
+        if (isPInvoke)
+        {
+            bool suppressGCTransition = false;
+            CorInfoCallConvExtension unmanagedCallConv = m_compHnd->getUnmanagedCallConv(methodHnd, sigInfo, &suppressGCTransition);
+            if (callConvIsInstanceMethodCallConv(unmanagedCallConv))
+            {
+                BADCODE("thiscall with 0 arguments");
+            }
+        }
+    }
+}
+
 void InterpCompiler::EmitCall(CORINFO_RESOLVED_TOKEN* pConstrainedToken, bool readonly, bool tailcall, bool newObj, bool isCalli)
 {
     uint32_t token = getU4LittleEndian(m_ip + 1);
@@ -4379,6 +4397,8 @@ void InterpCompiler::EmitCall(CORINFO_RESOLVED_TOKEN* pConstrainedToken, bool re
             BADCODE("Vararg methods are not supported in interpreted code");
         }
 
+        CheckForPInvokeThisCallWithNoArgs(&callInfo.sig, NULL);
+
         callIFunctionPointerVar = m_pStackPointer[-1].var;
         m_pStackPointer--;
         calliCookie = m_compHnd->GetCookieForInterpreterCalliSig(&callInfo.sig);
@@ -4534,6 +4554,11 @@ void InterpCompiler::EmitCall(CORINFO_RESOLVED_TOKEN* pConstrainedToken, bool re
         }
     }
 
+    if (isPInvoke && !isMarshaledPInvoke)
+    {
+        CheckForPInvokeThisCallWithNoArgs(&callInfo.sig, callInfo.hMethod);
+    }
+
     // Process sVars
     int numArgsFromStack = callInfo.sig.numArgs + (newObj ? 0 : callInfo.sig.hasImplicitThis());
     int newObjThisArgLocation = newObj && !doCallInsteadOfNew ? 0 : INT_MAX;
diff --git a/src/coreclr/interpreter/compiler.h b/src/coreclr/interpreter/compiler.h
index fce9781d3846d8..481755b1d1c3d8 100644
--- a/src/coreclr/interpreter/compiler.h
+++ b/src/coreclr/interpreter/compiler.h
@@ -947,6 +947,7 @@ class InterpCompiler
     void    EmitPushSyncObject();
     void    EmitCallsiteCallout(CorInfoIsAccessAllowedResult accessAllowed, CORINFO_HELPER_DESC* calloutDesc);
     void    EmitCanAccessCallout(CORINFO_RESOLVED_TOKEN *pResolvedToken);
+    void    CheckForPInvokeThisCallWithNoArgs(CORINFO_SIG_INFO* sigInfo, CORINFO_METHOD_HANDLE methodHnd);
 
     // Var Offset allocator
     TArray<InterpInst*, MemPoolAllocator> *m_pActiveCalls;