[cfe-dev] Semantics of __CFConstantStringClassReference variable (clang crash in PR38615)

[Richard Smith via cfe-dev]

On Tue, 21 Aug 2018 at 17:09, Manoj Gupta via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hi,
>
> I am looking for some help regarding a clang crash  when building
> opencflite. The root cause of the crash is because clang tries to create a
> GlobalValue "__CFConstantStringClassReference"  but a variable of same name
> is also present in the source file.
>
> Crash location:
>
> https://github.com/llvm-mirror/clang/blob/master/lib/CodeGen/CodeGenModule.cpp#L4058
>
>   // If we don't already have it, get __CFConstantStringClassReference.
>   if (!CFConstantStringClassRef) {
>     llvm::Type *Ty = getTypes().ConvertType(getContext().IntTy);
>     Ty = llvm::ArrayType::get(Ty, 0);
>     llvm::GlobalValue *GV = cast<llvm::GlobalValue>(
>         CreateRuntimeVariable(Ty, "__CFConstantStringClassReference")); //
> Crashes here
>
> Opencflite also declares __CFConstantStringClassReference as a variable,
> https://github.com/nevali/opencflite/blob/03999700cf3b79975ae2f2e5f4100ea7096acb3a/CFInternal.h#L364
> :
>
> extern int __CFConstantStringClassReference[];
>
> I do not know the semantics of the name __CFConstantStringClassReference.
> Is this a reserved name and should opencflite not be declaring this
> variable ?
>

Yes, this is a reserved identifier and should generally not be declared by
user code. (In this case, though, it looks like the code is attempting to
find the variable introduced by Clang, and maybe we want to allow that?) In
any case, Clang shouldn't crash :)


> If so, appreciate any advice on how to fix the offending code.
>
> Or is this a  bug in clang?
>
> For reference, r327993 (https://reviews.llvm.org/rL327993)  introduced
> this code.
>
> Author:     Rafael Espindola <rafael.espindola at gmail.com>
> AuthorDate: Tue Mar 20 15:48:00 2018 +0000
>
>     Set dso_local for CFConstantStringClassReference.
>
>     This one cannot use setGVProperties since it has special logic for
>     when it is dllimport or not.
>     git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@*327993*
> 91177308-0d34-0410-b5e6-96231b3b80d8
>
> Thanks,
> Manoj
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