[cfe-dev] Should a "typeinfo" variable be "linkonce_odr constant" or just "constant"

[Reid Kleckner]

Anders Carlsson added this logic to CGRTTI.cpp in r124096.  Currently it
lives in ItaniumCXXABI.cpp.

Anders, why is this necessary?


On Tue, Aug 5, 2014 at 7:06 AM, Kostya Serebryany <kcc at google.com> wrote:

> Hello Clang folks,
>
> I have a question about typeinfo variables:
>
> % cat a1.cc
> struct AAA {
>  public:
>   virtual ~ AAA ();
> };
> AAA::~AAA() { }
> void foo () { throw AAA (); }
>
> % clang++ a1.cc -S -o - -emit-llvm    | grep '_ZTI3AAA.=.[^{]*' -o
> _ZTI3AAA = constant
>
> % clang++ a1.cc -S -o - -emit-llvm  -fno-rtti  | grep '_ZTI3AAA.=.[^{]*'
> -o
> _ZTI3AAA = linkonce_odr constant
>
> As you can see, depending on the compilation mode (-fno-rtti) the
> definition of _ZTI3AAA
> (typeinfo for AAA) is different.  Is that expected?
>
> This difference causes problem for AddressSanitizer, if one part of the
> code is built with
> -fno-rtti and another part w/o -fno-rtti.
> asan instruments global constants but can not instrument linkonce_odr
> variables,
> as a result we mix an instrumented and a non-instrumented global in the
> same binary.
> https://code.google.com/p/address-sanitizer/issues/detail?id=327
>
> Thanks,
>
> --kcc
>
>
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>
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