Index: llvm/lib/Target/ARM/ARMISelLowering.cpp
===================================================================
--- llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -4431,13 +4431,26 @@
   }
 
   // varargs
-  if (isVarArg && MFI.hasVAStart())
-    VarArgStyleRegisters(CCInfo, DAG, dl, Chain,
-                         CCInfo.getNextStackOffset(),
+  if (isVarArg && MFI.hasVAStart()) {
+    VarArgStyleRegisters(CCInfo, DAG, dl, Chain, CCInfo.getNextStackOffset(),
                          TotalArgRegsSaveSize);
+    if (AFI->isCmseNSEntryFunction()) {
+      DiagnosticInfoUnsupported Diag(
+          DAG.getMachineFunction().getFunction(),
+          "secure entry function must not be variadic", dl.getDebugLoc());
+      DAG.getContext()->diagnose(Diag);
+    }
+  }
 
   AFI->setArgumentStackSize(CCInfo.getNextStackOffset());
 
+  if (CCInfo.getNextStackOffset() > 0 && AFI->isCmseNSEntryFunction()) {
+    DiagnosticInfoUnsupported Diag(
+        DAG.getMachineFunction().getFunction(),
+        "secure entry function requires arguments on stack", dl.getDebugLoc());
+    DAG.getContext()->diagnose(Diag);
+  }
+
   return Chain;
 }
 
Index: llvm/test/CodeGen/ARM/cmse-errors.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/ARM/cmse-errors.ll
@@ -0,0 +1,74 @@
+; RUN: not llc -mtriple=thumbv8m.main-eabi %s -o - 2>&1 | FileCheck %s
+
+%struct.two_ints = type { i32, i32 }
+%struct.__va_list = type { i8* }
+
+define void @test1(%struct.two_ints* noalias nocapture sret align 4 %agg.result) "cmse_nonsecure_entry" {
+entry:
+  %0 = bitcast %struct.two_ints* %agg.result to i64*
+  store i64 8589934593, i64* %0, align 4
+  ret void
+}
+; CHECK: error: {{.*}}test1{{.*}}: secure entry function would return value through pointer
+
+define void @test2(i32 %a, i32 %b, i32 %c, i32 %d, i32 %e) "cmse_nonsecure_entry" {
+entry:
+  ret void
+}
+; CHECK: error: {{.*}}test2{{.*}}:  secure entry function requires arguments on stack 
+
+define void @test3(void (i32, i32, i32, i32, i32)* nocapture %p) {
+entry:
+  tail call void %p(i32 1, i32 2, i32 3, i32 4, i32 5) "cmse_nonsecure_call"
+  ret void
+}
+; CHECK: error: {{.*}}test3{{.*}}: call to non-secure function would require passing arguments on stack
+
+
+define void @test4(void (%struct.two_ints*)* nocapture %p) {
+entry:
+  %r = alloca %struct.two_ints, align 4
+  %0 = bitcast %struct.two_ints* %r to i8*
+  call void %p(%struct.two_ints* nonnull sret align 4 %r) "cmse_nonsecure_call"
+  ret void
+}
+; CHECK: error: {{.*}}test4{{.*}}: call to non-secure function would return value through pointer
+
+declare void @llvm.va_start(i8*) "nounwind"
+
+declare void @llvm.va_end(i8*) "nounwind"
+
+define i32 @test5(i32 %a, ...) "cmse_nonsecure_entry" {
+entry:
+  %vl = alloca %struct.__va_list, align 4
+  %0 = bitcast %struct.__va_list* %vl to i8*
+  call void @llvm.va_start(i8* nonnull %0)
+  %1 = getelementptr inbounds %struct.__va_list, %struct.__va_list* %vl, i32 0, i32 0
+  %argp.cur = load i8*, i8** %1, align 4
+  %argp.next = getelementptr inbounds i8, i8* %argp.cur, i32 4
+  store i8* %argp.next, i8** %1, align 4
+  %2 = bitcast i8* %argp.cur to i32*
+  %3 = load i32, i32* %2, align 4
+  call void @llvm.va_end(i8* nonnull %0)
+  ret i32 %3
+}
+; CHECK: error: {{.*}}test5{{.*}}: secure entry function must not be variadic
+
+define void @test6(void (i32, ...)* nocapture %p) {
+entry:
+  tail call void (i32, ...) %p(i32 1, i32 2, i32 3, i32 4, i32 5) "cmse_nonsecure_call"
+  ret void
+}
+; CHECK: error: {{.*}}test6{{.*}}: call to non-secure function would require passing arguments on stack
+
+define void @neg_test1(void (i32, ...)* nocapture %p)  {
+entry:
+  tail call void (i32, ...) %p(i32 1, i32 2, i32 3, i32 4) "cmse_nonsecure_call"
+  ret void
+}
+
+define void @neg_test2(i32 %a, ...) "cmse_nonsecure_entry" {
+entry:
+  ret void
+}
+; CHECK-NOT: error: