[Clang][ICE] Corrected invalid invalid parameter index on some attributes with invalid indices applied to varargs functions

[aaron.ballman]

Thanks for working on this fix! A few things:

• Please add a summary description to the patch, and be sure to include a reference to the github issue in the summary.
• All functional changes (e.g., not typo fixes, fixes to comments, or other NFC changes) need test coverage that demonstrates the issue has been resolved.
• All functional changes should have a release note in clang/docs/ReleaseNotes.rst

clang/lib/Sema/SemaDeclAttr.cpp

3764–3767

Did you look into fixing this within checkFunctionOrMethodParameterIndex() instead? That way, all callers of the API get the correct behavior instead of having to find individual attributes to check the logic (I believe there are other attributes with the same underlying problem).

[erichkeane]

clang/lib/Sema/SemaDeclAttr.cpp

3764–3767

I would also expect any such issue to diagnose. Also, isn't there an off-by-one error here in the case of variadic args?

[tbaeder]

clang/lib/Sema/SemaDeclAttr.cpp

3764–3767

handleFormatAttr() has:

if (Idx < 1 || Idx > NumArgs) {
  S.Diag(AL.getLoc(), diag::err_attribute_argument_out_of_bounds)
      << AL << 2 << IdxExpr->getSourceRange();
  return;
}

which is also what I'd expect to see here.

[shafik]

clang/lib/Sema/SemaDeclAttr.cpp

3764–3767

I agree w/ @aaron.ballman here we should handle this in checkFunctionOrMethodParameterIndex it is used in many places and AFAICT they all have the same issue, none diagnose this case but paper it over.

There is definitely a bigger clean-up here but we can do a targeted fix now and remove a crash bug and leave the larger fixing for a follow-up.

[shafik]

For the benefit of those who have not seen the bug report: https://github.com/llvm/llvm-project/issues/61635

clang/lib/Sema/SemaDeclAttr.cpp

D->addAttr(::new (S.Context)
                  EnumExtensibilityAttr(S.Context, AL, ExtensibilityKind));
 }
 
 /// Handle __attribute__((format_arg((idx)))) attribute based on
 /// http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html
 static void handleFormatArgAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
   Expr *IdxExpr = AL.getArgAsExpr(0);
   ParamIdx Idx;
   if (!checkFunctionOrMethodParameterIndex(S, D, AL, 1, IdxExpr, Idx))
     return;
-
+  if (Idx.getASTIndex() >= getFunctionOrMethodNumParams(D))
+    return;
   // Make sure the format string is really a string.
   QualType Ty = getFunctionOrMethodParamType(D, Idx.getASTIndex());
 
   bool NotNSStringTy = !isNSStringType(Ty, S.Context);
   if (NotNSStringTy &&
       !isCFStringType(Ty, S.Context) &&
       (!Ty->isPointerType() ||
        !Ty->castAs<PointerType>()->getPointeeType()->isCharType())) {