Warn when calling a non interrupt function from an interrupt on ARM

The idea for this originated from a really tricky bug: ISRs on ARM don't
automatically save off the VFP regs, so if say, memcpy gets interrupted and the
ISR itself calls memcpy, the regs are left clobbered when the ISR is done.

https://reviews.llvm.org/D28820


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@292375 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Basic/DiagnosticSemaKinds.td

@@ -259,6 +259,9 @@ def err_anyx86_interrupt_attribute : Error<
   "a pointer as the first parameter|a %2 type as the second parameter}1">;
 def err_anyx86_interrupt_called : Error<
   "interrupt service routine cannot be called directly">;
+def warn_arm_interrupt_calling_convention : Warning<
+   "call to function without interrupt attribute could clobber interruptee's VFP registers">,
+   InGroup<Extra>;
 def warn_mips_interrupt_attribute : Warning<
    "MIPS 'interrupt' attribute only applies to functions that have "
    "%select{no parameters|a 'void' return type}0">,

lib/Sema/SemaExpr.cpp

@@ -5395,6 +5395,15 @@ Sema::BuildResolvedCallExpr(Expr *Fn, NamedDecl *NDecl,
     return ExprError();
   }
+  // Interrupt handlers don't save off the VFP regs automatically on ARM,
+  // so there's some risk when calling out to non-interrupt handler functions
+  // that the callee might not preserve them. This is easy to diagnose here,
+  // but can be very challenging to debug.
+  if (auto *Caller = getCurFunctionDecl())
+    if (Caller->hasAttr<ARMInterruptAttr>())
+      if (!FDecl->hasAttr<ARMInterruptAttr>())
+        Diag(Fn->getExprLoc(), diag::warn_arm_interrupt_calling_convention);
+
   // Promote the function operand.
   // We special-case function promotion here because we only allow promoting
   // builtin functions to function pointers in the callee of a call.

test/Sema/arm-interrupt-attr.c

@@ -17,3 +17,14 @@ __attribute__((interrupt("UNDEF"))) void foo7() {}
 __attribute__((interrupt)) void foo8() {}
 __attribute__((interrupt())) void foo9() {}
 __attribute__((interrupt(""))) void foo10() {}
+
+void callee1();
+__attribute__((interrupt("IRQ"))) void callee2();
+void caller1() {
+  callee1();
+  callee2();
+}
+__attribute__((interrupt("IRQ"))) void caller2() {
+  callee1(); // expected-warning {{call to function without interrupt attribute could clobber interruptee's VFP registers}}
+  callee2();
+}