[clang][ARM] Emit an error when an interrupt handler is called.

Closes #95359.

Author: chrisnc

clang/docs/ReleaseNotes.rst

@@ -696,6 +696,8 @@ Improvements to Clang's diagnostics
 - Clang no longer emits a "no previous prototype" warning for Win32 entry points under ``-Wmissing-prototypes``.
   Fixes #GH94366.
 
+- For the ARM target, calling an interrupt handler from another function is now an error. #GH95359.
+
 Improvements to Clang's time-trace
 ----------------------------------
 

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -340,6 +340,8 @@ def warn_arm_interrupt_vfp_clobber : Warning<
   "interrupt service routine with vfp enabled may clobber the "
   "interruptee's vfp state">,
   InGroup<DiagGroup<"arm-interrupt-vfp-clobber">>;
+def err_arm_interrupt_called : Error<
+  "interrupt service routine cannot be called directly">;
 def warn_interrupt_attribute_invalid : Warning<
    "%select{MIPS|MSP430|RISC-V}0 'interrupt' attribute only applies to "
    "functions that have %select{no parameters|a 'void' return type}1">,

clang/lib/Sema/SemaExpr.cpp

@@ -6625,9 +6625,15 @@ ExprResult Sema::BuildResolvedCallExpr(Expr *Fn, NamedDecl *NDecl,
   unsigned BuiltinID = (FDecl ? FDecl->getBuiltinID() : 0);
 
   // Functions with 'interrupt' attribute cannot be called directly.
-  if (FDecl && FDecl->hasAttr<AnyX86InterruptAttr>()) {
-    Diag(Fn->getExprLoc(), diag::err_anyx86_interrupt_called);
-    return ExprError();
+  if (FDecl) {
+    if (FDecl->hasAttr<AnyX86InterruptAttr>()) {
+      Diag(Fn->getExprLoc(), diag::err_anyx86_interrupt_called);
+      return ExprError();
+    }
+    if (FDecl->hasAttr<ARMInterruptAttr>()) {
+      Diag(Fn->getExprLoc(), diag::err_arm_interrupt_called);
+      return ExprError();
+    }
   }
 
   // X86 interrupt handlers may only call routines with attribute

clang/test/Sema/arm-interrupt-attr.c

@@ -1,8 +1,10 @@
-// RUN: %clang_cc1 %s -triple arm-none-eabi -DSOFT -verify -fsyntax-only
+// RUN: %clang_cc1 %s -triple arm-none-eabi -verify -fsyntax-only
 // RUN: %clang_cc1 %s -triple arm-none-eabi -target-feature +vfp2 -verify -fsyntax-only
 
 
-#ifdef SOFT
+#ifdef __ARM_FP
+__attribute__((interrupt("IRQ"))) void float_irq(void); // expected-warning {{interrupt service routine with vfp enabled may clobber the interruptee's vfp state}}
+#else // !defined(__ARM_FP)
 __attribute__((interrupt("irq"))) void foo1(void) {} // expected-warning {{'interrupt' attribute argument not supported: irq}}
 __attribute__((interrupt(IRQ))) void foo(void) {} // expected-error {{'interrupt' attribute requires a string}}
 __attribute__((interrupt("IRQ", 1))) void foo2(void) {} // expected-error {{'interrupt' attribute takes no more than 1 argument}}
@@ -14,6 +16,11 @@ __attribute__((interrupt("UNDEF"))) void foo7(void) {}
 __attribute__((interrupt)) void foo8(void) {}
 __attribute__((interrupt())) void foo9(void) {}
 __attribute__((interrupt(""))) void foo10(void) {}
-#else
-__attribute__((interrupt("IRQ"))) void float_irq(void); // expected-warning {{interrupt service routine with vfp enabled may clobber the interruptee's vfp state}}
-#endif
+
+__attribute__((interrupt("IRQ"))) void callee(void) {}
+
+void caller(void)
+{
+    callee(); // expected-error {{interrupt service routine cannot be called directly}}
+}
+#endif // __ARM_FP