diff --git a/llvm/lib/Target/BPF/BPFISelLowering.cpp b/llvm/lib/Target/BPF/BPFISelLowering.cpp
--- a/llvm/lib/Target/BPF/BPFISelLowering.cpp
+++ b/llvm/lib/Target/BPF/BPFISelLowering.cpp
@@ -35,22 +35,20 @@
   cl::Hidden, cl::init(false),
   cl::desc("Expand memcpy into load/store pairs in order"));
 
-static void fail(const SDLoc &DL, SelectionDAG &DAG, const Twine &Msg) {
-  MachineFunction &MF = DAG.getMachineFunction();
-  DAG.getContext()->diagnose(
-      DiagnosticInfoUnsupported(MF.getFunction(), Msg, DL.getDebugLoc()));
-}
-
-static void fail(const SDLoc &DL, SelectionDAG &DAG, const char *Msg,
-                 SDValue Val) {
-  MachineFunction &MF = DAG.getMachineFunction();
+[[noreturn]] static void fail(const SDLoc &DL, SelectionDAG &DAG,
+                              const Twine &Msg,
+                              std::optional<SDValue> Val = std::nullopt) {
   std::string Str;
   raw_string_ostream OS(Str);
-  OS << Msg;
-  Val->print(OS);
+  Function &F = DAG.getMachineFunction().getFunction();
+  OS << "in function " << F.getName() << ' ' << F.getFunctionType() << ": "
+     << Msg;
+  if (Val.has_value()) {
+    Val.value()->print(OS);
+  }
+  OS << '\n';
   OS.flush();
-  DAG.getContext()->diagnose(
-      DiagnosticInfoUnsupported(MF.getFunction(), Str, DL.getDebugLoc()));
+  report_fatal_error(Twine(Str));
 }
 
 BPFTargetLowering::BPFTargetLowering(const TargetMachine &TM,
@@ -261,7 +259,8 @@
   uint32_t Opcode = N->getOpcode();
   switch (Opcode) {
   default:
-    report_fatal_error("Unhandled custom legalization");
+    err_msg = "Unhandled custom legalization";
+    break;
   case ISD::ATOMIC_LOAD_ADD:
   case ISD::ATOMIC_LOAD_AND:
   case ISD::ATOMIC_LOAD_OR:
@@ -303,7 +302,7 @@
     SelectionDAG &DAG, SmallVectorImpl<SDValue> &InVals) const {
   switch (CallConv) {
   default:
-    report_fatal_error("Unsupported calling convention");
+    fail(DL, DAG, "Unsupported calling convention");
   case CallingConv::C:
   case CallingConv::Fast:
     break;
@@ -317,15 +316,17 @@
   CCState CCInfo(CallConv, IsVarArg, MF, ArgLocs, *DAG.getContext());
   CCInfo.AnalyzeFormalArguments(Ins, getHasAlu32() ? CC_BPF32 : CC_BPF64);
 
-  for (auto &VA : ArgLocs) {
+  size_t NumExcessArgs = 0;
+  for (size_t I = 0; I < ArgLocs.size(); ++I) {
+    auto &VA = ArgLocs[I];
     if (VA.isRegLoc()) {
       // Arguments passed in registers
       EVT RegVT = VA.getLocVT();
       MVT::SimpleValueType SimpleTy = RegVT.getSimpleVT().SimpleTy;
       switch (SimpleTy) {
       default: {
-        errs() << "LowerFormalArguments Unhandled argument type: "
-               << RegVT << '\n';
+        errs() << "LowerFormalArguments Unhandled argument type: " << RegVT
+               << '\n';
         llvm_unreachable(nullptr);
       }
       case MVT::i32:
@@ -349,13 +350,19 @@
 
         InVals.push_back(ArgValue);
 
-	break;
+        break;
       }
     } else {
-      fail(DL, DAG, "defined with too many args");
-      InVals.push_back(DAG.getConstant(0, DL, VA.getLocVT()));
+      NumExcessArgs++;
     }
   }
+  if (NumExcessArgs != 0) {
+    std::string Str;
+    raw_string_ostream OS(Str);
+    OS << "attempts to read " << NumExcessArgs
+       << " args from the stack, defined with too many args";
+    fail(DL, DAG, Str);
+  }
 
   if (IsVarArg || MF.getFunction().hasStructRetAttr()) {
     fail(DL, DAG, "functions with VarArgs or StructRet are not supported");
@@ -384,7 +391,7 @@
 
   switch (CallConv) {
   default:
-    report_fatal_error("Unsupported calling convention");
+    fail(CLI.DL, DAG, "Unsupported calling convention");
   case CallingConv::Fast:
   case CallingConv::C:
     break;